MESSENGER: The Science Phase

See new, spectacular, or mysterious sky images.
User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: The Science Phase

Post by bystander » Fri Apr 08, 2011 9:42 pm

MESSENGER Kicks Off Yearlong Campaign of Mercury Science
NASA JHU-APL CIW | MESSENGER | 2011 Apr 04

This afternoon, MESSENGER began its yearlong science campaign to understand the innermost planet. The spacecraft will fly around Mercury 700 times over the next 12 months, and its instruments will perform the first complete reconnaissance of the cratered planet’s geochemistry, geophysics, geological history, atmosphere, magnetosphere, and plasma environment.

“MESSENGER’s orbital commissioning phase, which we just completed, demonstrated that the spacecraft and payload are all operating nominally, notwithstanding Mercury’s challenging environment,” says Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “With the beginning today of the primary science phase of the mission, we will be making nearly continuous observations that will allow us to gain the first global perspective on the innermost planet. Moreover, as solar activity steadily increases, we will have a front-row seat on the most dynamic magnetosphere–atmosphere system in the Solar System.”

MESSENGER’s 12-month orbital phase covers two Mercury solar days (one Mercury solar day, from sunrise to sunrise, is equal to 176 Earth days). This means that the spacecraft can view a given spot on the surface under given lighting conditions only twice during the mission, six months apart, making available observation time a precious resource. “So the surface mapping observations had to be planned for the entire year far in advance to ensure coverage of the entire planet under acceptable illumination and viewing geometries,” says MESSENGER Deputy Project Scientist Brian Anderson, who oversaw the planning for orbital operations.

SciBox – a suite of software tools for science observation simulation– was developed to help the team choreograph the complicated process of maximizing the scientific return from the mission and minimizing conflicts between instrument observations, while at the same time meeting all spacecraft constraints on pointing, data downlink rates, and onboard data storage capacity. The SciBox tool simulates the entire year of science observations and identifies the best times to take each type of observation. The commands for each week of observations are derived from this full mission analysis.

For instance, Anderson explains, “The remote sensing instruments to measure topography and determine surface and atmospheric composition are fixed on the spacecraft and share the same view direction. Because the ideal viewing directions for these instruments are not the same, we assigned altitude ranges for which the spacecraft pointing is optimized for the science from each instrument. “The camera has its own pivot, so it has much greater freedom in viewing the surface and it takes pictures at all altitudes,” he continues. “Several other instruments make measurements of local properties, magnetic field, or charged particles and acquire excellent data regardless of the spacecraft pointing.”

SciBox works by finding the best opportunities for each of the instruments to make their measurements and then analyzing how those measurements contribute toward the science goals of the entire mission. “The SciBox tool allows us to plan thousands of science observation activities every week that have to be precisely timed with customized spacecraft pointing,” Anderson says.

The observations depend critically on where the spacecraft is in its orbit around Mercury, so the final science observation plan was not generated until the MESSENGER spacecraft completed Mercury orbit insertion. The software commands for this week’s instrument operations were sent to MESSENGER only last week.

“We had to wait until after MESSENGER was in orbit before we could start building the actual science sequences that start today, because we needed the actual in-orbit ephemeris as calculated by our navigation team to ensure that images and other pointed observations were taken where planned,” explains MESSENGER Payload Operations Manager Alice Berman.

On March 21, her team received the first ephemeris following Mercury orbit insertion, a delivery that provided less than two weeks for each instrument payload lead to generate inputs, test them, and deliver them to the mission operations team. That team then had to merge those science observation commands with the spacecraft operating commands and fully test the entire package.

For example, the command load for this week’s observations provides for the acquisition of 4,196 images by the Mercury Dual Imaging System (MDIS). The MDIS team had to check the commands governing each of those images; and the guidance and control team next had to run detailed software simulations on all the science guidance and control commands for the entire week and then add the non-science commands, such as those directing solar panel motions and star trackers. Finally the team re-simulated the full sequence again.

“It’s a tremendous amount of work and analysis that has to be done every week,” Berman notes. “From our experience with the In-the-Life exercises over the last two years, we determined that we would need three weeks for that process. But our entire team did an outstanding job getting it all done on the accelerated schedule.”

Imaging during the MESSENGER flybys provided important reconnaissance for the observations from orbit. During MESSENGER’s first six months in orbit, MDIS will create new, higher resolution, global maps of the planet in color and monochrome, acquired under near-ideal viewing conditions.

Emphasis during the second six months will shift to targeted, high-resolution imaging with the MDIS narrow-angle camera and acquisition of a second monochrome map but from a different viewing direction to allow stereoscopic analysis of topography. Additionally,
  • The Mercury Laser Altimeter will measure the topography of the northern hemisphere over four Mercury years.
  • The Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer will yield global maps of elemental composition.
  • The Magnetometer will measure the vector magnetic field under a range of solar distances and conditions.
  • The Visible and Infrared Spectrograph will produce global maps of surface reflectance from which surface mineralogy can be inferred, and the Ultraviolet and Visible Spectrometer will produce time-dependent global maps of exospheric species abundances versus altitude.
  • The Energetic Particle and Plasma Spectrometer will sample the plasma and energetic particle population in the solar wind, at major magnetospheric boundaries, and throughout the environment of Mercury at a range of solar distances and levels of solar activity.
  • The radio science experiment will extend topographic information to the southern hemisphere by making occultation measurements of planet radius, and the planet’s obliquity and the amplitude of the physical libration will be determined independently from the topography and gravity field.

MESSENGER orbits Mercury twice every Earth day. Once a day, the spacecraft will stop making measurements and turn its antenna toward Earth for eight hours to send data back – via the Deep Space Network – to the MESSENGER Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

“The engineering teams accomplished an astonishing achievement by developing, launching, and guiding MESSENGER through the inner solar system and safely placing the spacecraft in orbit about Mercury” says Anderson. “Now the science planning teams are working hard to take full advantage of this unprecedented opportunity to learn everything we can about Earth’s heretofore enigmatic sibling planet. With thousands of science observation commands to plan, test, and verify every week, not to mention the need to verify that the observations are successful, we certainly have our work cut out for us,” Anderson says. “But we have the tools, the people, and the processes in place to do the job. So far, everything is going just the way we planned.”
Where is MESSENGER?

You can follow MESSENGER’s journey in its orbit about Mercury with the newly revised "Where Is MESSENGER?" website feature, which offers simulated views of the spacecraft’s current orbit and what Mercury looks like from MESSENGER’s current perspective. The Solar System Simulator offers another option for portraying Mercury from the perspective of the MESSENGER spacecraft at any time during the remainder of the mission. Simulated views of nearby Mercury or distant Earth from MESSENGER may be created for a variety of fields of view.

For complete information on MESSENGER’s Mercury orbital operations, go online to http://messenger.jhuapl.edu/mer_orbit.html.
MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a yearlong study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington (CIW), leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory (JHU APL) built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.
Let the Science Phase Begin!
NASA JHU-APL CIW | MESSENGER | 2011 Apr 06
With the commissioning phase completed, the spacecraft and instruments have been checked out and are ready to enter the primary science phase of the mission. Over the next year, MESSENGER's suite of scientific instruments will gather unprecedented data about the Solar System's innermost planet to unravel Mercury's mysteries.

During this period, the MDIS team will be posting a new image each workday to this spot on the website. Check back often to see the latest images from the first orbital mission to Mercury!

This image was captured during the first science orbit of the mission. The crater crossing the top center of the image is Li Ch'ing-Chao. Li Ch'ing-Chao is located in Mercury's south polar region, near Boccaccio and Camoes.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury? section of this website to learn more about the key science questions that the MESSENGER mission is addressing. During the one-year primary mission, MDIS is scheduled to acquire more than 75,000 images in support of MESSENGER's science goals.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Bright Rays of Kuiper and Dark Material Near Hitomaro
NASA JHU-APL CIW | MESSENGER | 2011 Apr 07
The rayed crater in the bottom left corner of this image is Kuiper. The crater Hitomaro, located to the east of Kuiper, has nearby dark material.

This image was acquired as part of MDIS's color base map. The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface with an average resolution of 1 kilometer/pixel (0.6 miles/pixel). The highest-quality color images are obtained for Mercury's surface when both the spacecraft and the Sun are overhead, so these images typically are taken with viewing conditions of low incidence and emission angles.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Mercury, as Seen in High Resolution
NASA JHU-APL CIW | MESSENGER | 2011 Apr 08
As the MESSENGER spacecraft sped over Mercury's north polar region, the NAC captured this image in very high resolution. This area is located north of Hokusai.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
BMAONE23
Commentator Model 1.23
Posts: 4076
Joined: Wed Feb 23, 2005 6:55 pm
Location: California

Re: MESSENGER: Let the Science Phase Begin!

Post by BMAONE23 » Sat Apr 09, 2011 1:04 pm

Looking at that last image, there appear to be many newer smaller craters and some larger older "weathered" craters.
Mercury has a tenuous atmosphere but I don't think it would be capable of producing such weathering. Could the Solar Winds be responsible?

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: MESSENGER: Let the Science Phase Begin!

Post by neufer » Sat Apr 09, 2011 2:46 pm

BMAONE23 wrote:
Looking at that last image, there appear to be many newer smaller craters and some larger older "weathered" craters.
Mercury has a tenuous atmosphere but I don't think it would be capable of producing such weathering. Could the Solar Winds be responsible?
Unlikely.

Perhaps it is due to a constant rain of micrometeorites much heavier than that which rains down on the Moon.
http://en.wikipedia.org/wiki/List_of_craters_on_Mercury wrote:
<<Over all of Mercury, the crispness of crater rims and the morphology of their walls, central peaks, ejecta deposits, and secondary-crater fields have undergone systematic changes with time. The youngest craters or basins in a local stratigraphic sequence have the sharpest, crispest appearance. The oldest craters consist only of shallow depressions with slightly raised, rounded rims, some incomplete. On this basis, five age categories of craters and basins have been mapped; the characteristics of each are listed in the explanation. In addition, secondary crater fields are preserved around proportionally far more craters and basins on Mercury than on the Moon or Mars, and are particularly useful in determining overlap relations and degree of modification.>>
Art Neuendorffer

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 April 10-19

Post by bystander » Mon Apr 11, 2011 3:23 pm

Old Friends
NASA JHU-APL CIW | MESSENGER | 2011 Apr 11
First seen in Mariner 10 images, and again during MESSENGER's second flyby of Mercury, the bright-rayed crater Kuiper (62 km in diameter) provides an important stratigraphic marker in Mercury's history. The craters Calvino (67 km) and Rudaki (123 km), imaged at some of the highest resolution color obtained prior to orbit, are seen at the bottom left (northeast is up).

This image was acquired as part of MDIS's color base map. The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface with an average resolution of 1 kilometer/pixel (0.6 miles/pixel). The highest-quality color images are obtained for Mercury's surface when both the spacecraft and the Sun are overhead, so these images typically are taken with viewing conditions of low incidence and emission angles.

Bek and Lermontov
NASA JHU-APL CIW | MESSENGER | 2011 Apr 12
Pictured here are two named craters, Bek (32 km in diameter) and Lermontov (166 km in diameter). Bek's beautiful rays are indicative of its relative youth; Lermontov's floor is a suspected site of explosive volcanism, with irregular depressions and a distinct color signature.

This image was acquired as part of MDIS's color base map. The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface with an average resolution of 1 kilometer/pixel (0.6 miles/pixel). The highest-quality color images are obtained for Mercury's surface when both the spacecraft and the Sun are overhead, so these images typically are taken with viewing conditions of low incidence and emission angles.

Bek's Close Up
NASA JHU-APL CIW | MESSENGER | 2011 Apr 13
This oblique image of Bek (32 km in diameter) is a higher-resolution NAC complement to yesterday's WAC image. The sharp crater rim is in contrast to its subdued surroundings, where crater ejecta scoured the surface and left behind many secondary craters.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Unnamed Peaks
NASA JHU-APL CIW | MESSENGER | 2011 Apr 14
The mounds in this image are the central peak of an unnamed crater approximately 47 km in diameter, imaged at such high resolution (18 meters/pixel) that only the crater's interior can be seen. Central peaks are of great interest because they expose material that originally resided at depth in the target material.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Praxiteles' Highs and Lows
NASA JHU-APL CIW | MESSENGER | 2011 Apr 15
Praxiteles is a peak-ring basin with high-reflectance color features on its floor, suspected to be a result of past volcanic activity. Near the ring's peaks, depressions associated with high-reflectance material can be observed.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Don't Get Weird On Me, Babe
NASA JHU-APL CIW | MESSENGER | 2011 Apr 18
The large, smooth area in the upper left is the floor of the crater Petrarch. The more rugged terrain around Petrarch has an unusual "hilly and lineated" texture that Mariner 10 team members called "weird terrain" upon seeing it for the first time. This area may have been modified by converging seismic waves and/or ejecta from the formation of the Caloris basin, which is located on the opposite side of the planet. In April 2011, MESSENGER viewed this area under differing lighting conditions than those seen during MESSENGER's second flyby and Mariner 10's first pass.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Bright Peaks, Big Crater
NASA JHU-APL CIW | MESSENGER | 2011 Apr 19
This oblique-view image was obtained as a special targeted observation of the large crater Asvaghosa. This crater, 90 km (56 mi.) in diameter, has bright central peaks. Their high reflectance appears to have been enhanced by the crater ray that crosses the area, having originated either at Kuiper to the southwest, or Hokusai to the northeast.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of small areas on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.


Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury’s Exosphere: A Brief Overview
Science Highlights from Mercury Orbit | 2011 Apr 19
One of the primary science goals of MESSENGER is to study Mercury’s very thin atmosphere, or exosphere. Although observations of the exosphere from orbit have begun, these data must be carefully calibrated, and analysis is still underway. In the meantime, here is a primer on Mercury’s exosphere: what it is, how we observe it, and why it is important.

What Is Mercury’s Exosphere?

Mercury’s atmosphere is so tenuous that the atoms or molecules comprising it are more likely to escape from the planet or collide with the surface than to collide with one another. “Exosphere” is the term given to such an extremely thin atmosphere. Earth’s atmosphere also includes an exosphere, but that term applies only to the highest altitudes where our atmosphere blends into the near vacuum of space. At Mercury, however, the exosphere is the only atmosphere there is, and its lower boundary is the planetary surface. Mercury thus has what is termed a “surface-bounded” exosphere. To give one an idea of how thin Mercury’s exosphere really is, the surface pressure is 1/1,000,000,000,000th that of Earth’s atmosphere.
Where Does Mercury’s Exosphere Come from?

Mercury’s exosphere derives from a combination of planetary surface material, solar wind ions, and interplanetary dust particles that have impacted Mercury’s surface over time. The majority of Mercury’s exosphere is composed of atoms rather than molecules because atoms are easier to eject from the surface. Atoms of sodium, calcium (both neutral and ionized), magnesium, potassium, hydrogen, and helium have been observed in Mercury’s exosphere by MESSENGER, Mariner 10, and/or ground-based telescopes.

The processes that generate and maintain Mercury’s exosphere are illustrated in Figure 1. Low-energy processes include photon-stimulated desorption (PSD) and thermal evaporation. Both processes are the result of solar photons hitting Mercury’s surface. During PSD the solar photons directly release atoms from the surface; during thermal evaporation the photons heat the surface and the heat releases the atoms. Two high-energy processes — ion sputtering and meteoroid vaporization — result from the impacts onto the surface of solar wind and magnetospheric ions and small dust particles, respectively.

Because the atoms in Mercury’s exosphere do not collide with one another, once launched they follow ballistic trajectories under the influence of gravity. Atoms released with low energy generally return to the surface. Atoms released with high energy remain aloft for a longer period of time, which allows solar radiation pressure — the push by solar photons in the anti-sunward direction — to affect their trajectories. Radiation pressure affects different atoms to different degrees (e.g., sodium strongly, calcium weakly, magnesium insignificantly), so some atoms will eventually return to the surface whereas others will be accelerated far from the planet to form an extended comet-like tail. Most of the neutral atoms that make their way into the tail will escape the planet. At times, a sodium tail has been observed to extend more than two million miles from Mercury. Solar photons can also ionize atoms (by a process known as photoionization). Many of these photoions will be picked up by the solar wind and whisked away from the planet, but a fair number will be returned to the surface under the influence of Mercury’s magnetic field.

If all of the source processes for the exosphere were turned off, Mercury’s exosphere would disappear within a few days. That we always see the exosphere is testament to the dynamic nature of the interaction between the surface and the surrounding space environment.
How Do We Observe the Exosphere?

The primary means by which we study the exosphere of Mercury is through the observation of radiation emitted by the atoms. We observe what is called resonance emission, by which atoms absorb the energy of solar photons at a particular wavelength and then re-emit photons at that same wavelength. Because the wavelengths at which such emissions occur vary with the type of atom, each emission we observe carries a distinctive spectral fingerprint of a particular kind of atom.

The strength of the emission depends on the number of atoms we can see and a parameter called the g-factor, which is the probability of emission from an atom. G-factors can vary greatly among types of atom, so the brightest emission may not derive from the most abundant element. Although the observed emission brightness for sodium can be 100 times or more that of magnesium, for instance, the two types of atoms often have approximately equal densities because sodium radiates very efficiently whereas magnesium does not.

The Ultraviolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on MESSENGER was designed specifically to observe these atomic emissions. Figure 2 provides examples of such “emission line” observations by UVVS, as well as the spatial distributions of three species observed during MESSENGER’s third flyby. Differences in these distributions indicate that the controlling processes act on each constituent in different ways. UVVS will make hundreds of thousands of similar observations during MESSENGER’s orbital mission phase.

Why Is the Exosphere Important?

The exosphere is a reflection of ongoing and varied processes and represents a visible connection between the surface of Mercury and the space environment. Because the atoms in the exosphere all originate at Mercury’s surface, studying the composition of the exosphere can provide insight into the composition of the surface. The processes that control the exosphere can redistribute material across Mercury’s surface, so understanding those processes can tell us how the surface of Mercury is changing and, by extrapolation, how it has changed in the past (in other words, how the surface of Mercury has been “weathered” by the space environment). The exosphere is also the conduit for loss of material from Mercury, so observing how that material is lost — the processes, the rates, and the time variability — can further help us determine how Mercury’s surface has evolved with time. To understand the interaction between Mercury and its highly dynamic environment, we must study the exosphere.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: MESSENGER: Don't Get Weird On Me, Babe

Post by neufer » Tue Apr 19, 2011 8:01 pm

bystander wrote:Don't Get Weird On Me, Babe
NASA JHU-APL CIW | MESSENGER | 2011 Apr 18
The large, smooth area in the upper left is the floor of the crater Petrarch. The more rugged terrain around Petrarch has an unusual "hilly and lineated" texture that Mariner 10 team members called "weird terrain" upon seeing it for the first time. This area may have been modified by converging seismic waves and/or ejecta from the formation of the Caloris basin, which is located on the opposite side of the planet. In April 2011, MESSENGER viewed this area under differing lighting conditions than those seen during MESSENGER's second flyby and Mariner 10's first pass.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
http://www.planetary.org/blog/article/00003004/ wrote:
Mercury's Weird Terrain
The Planetary Society Blog By Emily Lakdawalla | Apr. 19, 2011
<<When Mariner 10 flew past Mercury, it caught an immense impact basin lying half in and half out of sunlight, which they named Caloris. Even with only half the basin visible, scientists knew it was one of the largest in the solar system. The Caloris Basin is one of the largest basins in the solar system at approximately 1,300 kilometers in diameter. Only half of it was seen by Mariner 10 as it sped past Mercury in 1974. Geologists had to wait more than 25 years to see the rest of Caloris, and when they did it turned out to be even bigger than they had thought. But the fact that Caloris was only half in sunlight was fortuitous in one sense, because it meant that the spot on Mercury that was exactly opposite the area of the Caloris impact was also partially in sunlight. That spot looks weird. In fact, this area has been referred to since Mariner 10 as the "weird terrain" on Mercury. And MESSENGER's orbital path has finally taken it over the weird terrain to get a good view. The MESSENGER photo doesn't make it immediately obvious what is going on geologically, but it does confirm that this "antipodal" terrain looks different from other areas of Mercury.

But why should terrain antipodal to Caloris look unusual? It represents the spot on Mercury that is as far as you can get from the impact site, so it seems like the spot that would be least affected by a giant impact. Surprisingly, the opposite is true: the point on Mercury that's farthest from the Caloris impact actually gets magnified effects; it's worse to be 180 degrees away from an impact than it is to be 175 degrees away. There are two reasons why; one comes from above, and the other from below.

The first has to do with where the ejecta flies. Ejecta from an impact travels outward in all directions, on roughly ballistic trajectories. For small impacts, those ballistic trajectories result in a splash-like deposit around the crater, a widening circle of deposits. But if the impact has enough energy, the material can go so far around the spherical planet that the ballistic trajectories start to converge again.

Ejecta travels above an impact. Below the impact, you get shock waves, which are very much like earthquake waves (specifically, the compression type of earthquake waves called P waves). A shock wave travels outward in all directions, and if that's all that happened there would be nothing special about the antipodal point. But waves, just like light, sound, and water waves, reflect and refract whenever they reach boundaries between two materials.

For Mercury there's two key boundaries: the boundary between planet and space (that is, the surface), and the boundary between the solid mantle and molten outer core. As the shock waves reflect from the surface, they bounce right around the planet to converge at the antipode. What's more, when the shock waves go from mantle to molten core, they slow down, refracting in a way that tends to focus them at the antipode; in a way, Mercury's core acts as a giant lens, focusing the shock waves to a spot antipodal to the impact site. The waves interfere constructively, piling on top of each other to shake the ground with much higher energy at the antipode than just a few degrees away from it.

This has actually been recorded on Earth, although it's rare. Seismic stations antipodal to large earthquakes have recorded larger than expected ground shaking. Detection is rare for several reasons. For one thing, Earth isn't a perfect sphere, so the convergence isn't perfect. Also, you have to be really close to 180 degrees away from the original earthquake, and the odds aren't great for there to be seismic stations located within two degrees of the antipodal point to a great big earthquake. It doesn't help that vast majority of land on Earth has ocean at the antipodal point.>>
Art Neuendorffer

User avatar
BMAONE23
Commentator Model 1.23
Posts: 4076
Joined: Wed Feb 23, 2005 6:55 pm
Location: California

Re: MESSENGER: This Erosion

Post by BMAONE23 » Wed Apr 20, 2011 9:29 pm

This erosion

This view of Mercury's surface illustrates the process of erosion on the innermost planet. At present on Earth, the dominant agents that work to wear down the landscape are flowing water, moving ice (glaciers), and blowing wind. Mercury lacks these agents, and its atmosphere is far too thin to offer protection from cosmic impacts.

Date acquired: April, 05, 2011

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

It would be interesting to send a lander there that would land on the night side just before sunrise and send back:
images of the sunrise, temperature increase data, atmospheric data, and solar wind influence data

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 April 20-25

Post by bystander » Thu Apr 21, 2011 3:57 am

This Erosion
NASA JHU-APL CIW | MESSENGER | 2011 Apr 20
This view of Mercury's surface illustrates the process of erosion on the innermost planet. At present on Earth, the dominant agents that work to wear down the landscape are flowing water, moving ice (glaciers), and blowing wind. Mercury lacks these agents, and its atmosphere is far too thin to offer protection from cosmic impacts. As a result, Mercury's surface is exposed to impact cratering by objects ranging from micrometer-sized dust motes to multi-kilometer asteroids and comets. Here we see craters in various stages of degradation. Some craters have been worn down to mere dimples, while other, younger, impacts still retain their original shapes. Craters that have a non-circular shape or that occur in clusters are probably secondary craters formed when material ejected from primary impacts falls back to the surface.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of small areas on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

The Ghost In You
NASA JHU-APL CIW | MESSENGER | 2011 Apr 21
Visible in this image are curving ridges, some of which form circular outlines. One is in the left corner, and several larger ones are arranged vertically down the center-right part of the image. These circular features mark the rims of "ghost craters" - impact craters that were subsequently buried by the voluminous volcanic lavas that form the plains in this part of Mercury. No doubt some craters were buried completely and now are entirely hidden, whereas others reveal their presence by the ridges that formed when the volcanic cover sagged over the crater rims or in response to modest horizontal contraction of the region.

This image was collected during the spacecraft's commissioning phase, shortly after entering orbit around Mercury. The original image was binned on the spacecraft from its original 1024 × 1024 pixel size to 512 × 512. Binning helps to reduce the amount of data that must be stored on the spacecraft's solid-state recorder and downlinked across interplanetary space from MESSENGER to the Deep Space Network on Earth. The image here has been placed into a map projection with north at the top.

String Section
NASA JHU-APL CIW | MESSENGER | 2011 Apr 22
This image covers one section of the 110-km diameter crater Abedin. The center of the crater, marked by central peak mountains, is at the lower left corner of the image. Strings of secondary craters, formed by blocks of material thrown out of the main crater, are arranged in a generally radial pattern leading away from the crater. The secondary craters are found at or beyond a distance of about one crater radius from the rim. The area adjacent to the rim is dominated by the crater's continuous ejecta blanket. The image was collected as part of MESSENGER's color base map. It was binned on the spacecraft from its original size of 1024 by 1024 pixels to 256 by 256.

MDIS's color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface with an average resolution of 1 kilometer/pixel (0.6 miles/pixel). The highest-quality color images are obtained for Mercury's surface when both the spacecraft and the Sun are overhead, so these images typically are taken with viewing conditions of low incidence and emission angles.

The Crater and the Scarp
NASA JHU-APL CIW | MESSENGER | 2011 Apr 23
This image is a mosaic of multiple NAC images. The crater in the center is being crossed by a scarp, such as those seen at Camoes and Thakur.

These images were acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

A New View of Spitteler and Holberg
NASA JHU-APL CIW | MESSENGER | 2011 Apr 24
Image
This image is a mosaic of multiple images. North is toward the upper right corner. The crater on the left of the image is Spitteler, while the neighboring crater to the right extending out the top of the image is Holberg. Both craters were viewed by Mariner 10, but MESSENGER's polar orbit offers a new view of these craters and the surrounding terrain.

Smile for the Camera
NASA JHU-APL CIW | MESSENGER | 2011 Apr 25
The crater with the "smile" (the large crater toward the top of the image) is Al-Hamadhani, named in 1979 for the tenth century Iranian author Badi' al-Zaman al-Hamadhani. This crater was first imaged by Mariner 10, but MESSENGER's Wide Angle Camera (WAC) now offers us another view.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
owlice
Guardian of the Codes
Posts: 8406
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: MESSENGER: Smile for the Camera

Post by owlice » Mon Apr 25, 2011 4:15 pm

That's one happy planet!
A closed mouth gathers no foot.

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 April 26-30

Post by bystander » Tue Apr 26, 2011 9:34 pm

Profiling Polar Craters with the Mercury Laser Altimeter
Science Highlights from Mercury Orbit | 2011 Apr 26
MESSENGER’s Mercury Laser Altimeter (MLA) uses a laser to measure the distance from the spacecraft to Mercury’s surface. The instrument sends a laser pulse to Mercury and measures the time it takes the light to bounce off the surface and return. Because we know the speed of light, we can convert the round-trip time to distance. Because we know the positions of the MESSENGER spacecraft and Mercury, we can determine the height of the terrain illuminated by the laser spot on the surface.
The laser sends pulses separated in time by about one-eighth of a second and provides measurements that are usually spaced about 600 meters (about 660 yards) apart on the surface. The MLA is sufficiently powerful to measure spacecraft-to-surface distances up to about 1,600 km (1,000 miles). When the laser beam hits Mercury’s surface, its footprint (or spot size) is between 15 and 100 meters in diameter, depending on distance, so MLA measures the average distance between the spacecraft and the surface over this area. The relative accuracy between measurements is better than 10 centimeters, (4 inches). A track from MLA, shown in Figure 1, contains the height measurements from one pass over Mercury’s surface.

Like all instruments on MESSENGER, MLA provides information for several different science investigations. The range measurements from MLA will be used to recover the overall shape of the planet, which helps determine Mercury’s interior structure. When MLA tracks cross deformational features such as ridges or scarps, the topographic profile provides information on how the landscape has adjusted in response to shortening or stretching of the crust. Comparing the change in elevation from one MLA measurement to the next gives an estimate of the roughness of the surface.

One of the most important tasks for MLA is to measure the depths of craters that are near Mercury’s north pole. Radar images of Mercury’s polar regions obtained as many as 20 years ago by radio telescopes on Earth show that the floors of many of these craters contain material that reflects radio waves very well (Figure 2). Many scientists believe that these reflective polar deposits consist of water ice, but whether this is the correct explanation remains to be proved. Because Mercury’s surface reaches temperatures as high as 450° Celsius (800° Fahrenheit), this explanation may seem surprising. However, the floors of craters near the poles are thought to be in permanent shadow, shielded from sunlight throughout the Mercury day and year. This situation arises because Mercury's axis of rotation is oriented nearly perpendicular to the planet's orbit, so that sunlight strikes the surface near the poles at a near-grazing angle. Because Mercury has no appreciable atmosphere, these areas without sunlight remain extremely cold.

MLA will test whether these craters are sufficiently deep that the floors are indeed in permanent shadow. Most of the craters are small, however, and it is challenging to aim MLA with sufficient accuracy to obtain a profile across the crater floor. The science team decided that a promising approach would be to obtain as many laser tracks as possible near the north pole and then to search for those measurements that fall inside shadowed craters.

This plan turned out better than expected. On the very first pass, shown in Figure 1, the laser track passed directly across a small, deep crater with a floor that is highly reflective to radar, one of the candidate locations for water ice (arrow in Figure 2). The low, blue part of the track (arrow in Figure 1 inset) is the portion within the crater. The crater floor displays the lowest elevations along the track and is sufficiently deep for the floor to be permanently shadowed.

Throughout MESSENGER's one-year primary mission, many more MLA measurements of floor depths of craters near the north pole are expected. With these data, we will be able to test whether the imaged locations of strong radar reflections always coincide with areas in permanent shadow.

For more information on the Mercury Laser Altimeter (MLA), see http://messenger.jhuapl.edu/instruments/MLA.html.

For more information on polar, radar-bright craters, and possible water ice on Mercury, see http://messenger.jhuapl.edu/why_mercury/q5.html.


That's No Moon...
NASA JHU-APL CIW | MESSENGER | 2011 Apr 26
This image, taken with MESSENGER's Wide Angle Camera (WAC), shows Mercury's heavily cratered surface. While Mercury's surface is often compared with that of Earth's Moon, Mercury and the Moon differ significantly in a number of important ways, including core size, presence of a global magnetic field, and surface composition. Mercury is a unique world, not just the Moon moved closer to the Sun!

The Bright Peaks of Mickiewicz
NASA JHU-APL CIW | MESSENGER | 2011 Apr 27
This high-resolution image of Mickiewicz crater was taken with MESSENGER's Narrow Angle Camera (NAC). The brightness of the peaks at the crater's center results from the illumination conditions (sunlight on the steep slopes), from down-slope movement of eroded material that continually exposes fresh rock, and likely from the composition of the peaks as well.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

X Marks the Spot
NASA JHU-APL CIW | MESSENGER | 2011 Apr 28
This image of an as-yet-unnamed crater was taken using the Mercury Dual Imaging System (MDIS) pivot and Narrow Angle Camera (NAC). The perpendicular lines that traverse the crater are secondary crater chains caused by ejecta from two primary impacts outside of the field of view.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Dürer Gets Its Close-up
NASA JHU-APL CIW | MESSENGER | 2011 Apr 29
This close-up view of the inner peak ring and main rim of Dürer basin (named for the German artist, mathematician and theorist Albrecht Dürer) was provided by MESSENGER's Narrow Angle Camera (NAC). Concentric ring structures such as these form during the impact that creates the basin; the number of rings and their characteristics depend on the size of the impact structure. An impact crater larger than about 200 km in diameter is generally called a "basin."

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
BMAONE23
Commentator Model 1.23
Posts: 4076
Joined: Wed Feb 23, 2005 6:55 pm
Location: California

Re: MESSENGER: X Marks the Spot

Post by BMAONE23 » Thu Apr 28, 2011 5:03 pm

bystander wrote:X Marks the Spot
NASA JHU-APL CIW | MESSENGER | 2011 Apr 28
This image of an as-yet-unnamed crater was taken using the Mercury Dual Imaging System (MDIS) pivot and Narrow Angle Camera (NAC). The perpendicular lines that traverse the crater are secondary crater chains caused by ejecta from two primary impacts outside of the field of view.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Rotate that image about 180 deg and you would be close to this

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 May 01-07

Post by bystander » Mon May 02, 2011 4:33 pm

Measuring Mercury's Surface Composition
Science Highlights from Mercury Orbit | 2011 May 03
MESSENGER carries a Gamma-Ray Spectrometer (GRS) that is capable of measuring and characterizing gamma-ray emissions from the surface of Mercury. Just like radio waves, visible light, and X-rays, gamma rays are a form of electromagnetic radiation, but with higher energies than those other types of radiation. Gamma rays coming from Mercury carry information about the concentrations of elements present on its surface, so observations from the MESSENGER GRS are being used to determine the surface composition of the planet. These results will then be applied to studying the formation and geologic history of Mercury.
[i][b]Figure 2.[/b] Two example gamma-ray spectra acquired by the MESSENGER Gamma-Ray Spectrometer, with gamma-ray count rates shown as a function of energy (keV, or kilo-electron volt, is a unit of energy). To the left is shown a gamma-ray spectrum collected while MESSENGER was far from the planet; to the right is a spectrum obtained close to the surface (less than 2000 km altitude). “BG” denotes background gamma-ray peaks. Two particular gamma rays, at 1460-keV resulting from potassium and at 1779-keV resulting from silicon, are highlighted, as they show clear enhancements near the surface. These data demonstrate the presence of potassium and silicon on Mercury's surface. Other unlabeled peaks in the gamma-ray spectra in this energy range result from galactic cosmic-ray interactions with the spacecraft and detector material.[/i]

Sources of Gamma Rays

Planetary gamma rays can be grouped into two categories: gamma rays produced during radioactive decay and those produced by galactic cosmic-ray interactions (Figure 1). Naturally occurring radioactive elements (e.g., thorium, uranium, potassium) can be found on the surfaces of all of the terrestrial planets. These elements emit gamma rays as part of their natural radioactive decay process.

Stable elements (e.g., iron, silicon, and oxygen) do not spontaneously release gamma rays, so they are not normally detectable with a gamma-ray spectrometer. However, because Mercury lacks a substantial atmosphere, its surface is constantly bombarded by galactic cosmic rays. Cosmic rays are primarily high-energy protons, and when they collide with the surface they produce neutrons that subsequently excite elemental nuclei through such processes as neutron scattering and neutron capture. The normally stable nuclei, converted to unstable “excited states,” emit gamma rays to shed the extra energy they received from the neutrons as they return to their stable forms. Each element emits gamma rays at diagnostic energies during this process, enabling the MESSENGER GRS to determine the surface abundances of such elements from a spectrum of gamma-ray flux versus energy.

The MESSENGER Gamma-Ray Spectrometer

The MESSENGER GRS detects gamma rays having energies from 300 to 8000 keV with a cylindrical block of high-purity germanium (HPGe). When a gamma ray enters the HPGe crystal, it ionizes germanium atoms, and a measurement of the number of ionized electrons reveals the deposited gamma-ray energy. The ionization signal in the HPGe crystal is very small and can be overwhelmed by the thermal motion of germanium atoms. To reduce this “noise” associated with the thermal motion, the HPGe crystal is cooled to cryogenic temperatures. Such cooling requires that the MESSENGER GRS instrument include a mechanical cooler and heat radiator in order to keep the crystal temperature near 90° Kelvin (below -300° Fahrenheit).

The MESSENGER GRS is now collecting gamma rays from Mercury's surface. As an example of data acquired by the GRS, Figure 2 compares gamma-ray spectra taken far from Mercury (left) with spectra obtained close to Mercury (right) in the energy range 1000 to 2000 keV. This energy range includes examples of the two types of gamma rays discussed above. Potassium gamma rays, at an energy of 1460 keV, are emitted during the radioactive decay of potassium atoms. Silicon gamma rays, at an energy of 1779 keV, result from neutron-inelastic-scattering reactions of cosmic rays with silicon atoms. Both types of gamma rays show larger intensities near Mercury and therefore indicate the detection of these elements from Mercury's surface. Other elements within the detection capability of GRS include iron, titanium, oxygen, thorium, and uranium. Converting the measured gamma-ray intensities to elemental concentrations requires a detailed analysis that accounts for factors such as reaction probabilities, detection efficiencies, variable viewing geometries, and background gamma rays. The MESSENGER Science Team is carrying out these analyses determine the composition of Mercury's surface materials and their implications for planetary formation and evolution.

For more information on MESSENGER's Gamma-Ray Spectrometer (GRS), see http://messenger.jhuapl.edu/instruments/GRNS.html.


To Ngoc Van's Central Pit
NASA JHU-APL CIW | MESSENGER | 2011 May 02
The two largest craters in this image are Burns (43 km in diameter) and To Ngoc Van (71 km in diameter). To Ngoc Van contains an irregularly shaped pit, similar to those seen inside of the craters Beckett, Picasso, and Gibran, among others.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Beautiful Bartok
NASA JHU-APL CIW | MESSENGER | 2011 May 03
The complex crater Bartok, named for the Hungarian composer and pianist Bela Bartok, contains a prominent central peak. Chains of secondary craters formed by Bartok's ejecta can be seen across the entire image.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Turn, Turn, Turn
NASA JHU-APL CIW | MESSENGER | 2011 May 04
This dramatic view of Mercury's limb includes Beethoven basin, which can be seen towards the center of the image. Compare Beethoven's appearance and distance from the terminator here to its appearance in this image, taken ten days before, to get a sense of Mercury's rotation rate.

This image was acquired as part of MDIS's limb imaging campaign. Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb. These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

Abedin's Ejecta
NASA JHU-APL CIW | MESSENGER | 2011 May 05
The long shadows created near the terminator accentuate the topography of Abedin's continuous ejecta blanket and secondary crater chains.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Meet Joe Green
NASA JHU-APL CIW | MESSENGER | 2011 May 06
The crater Verdi was named in 1979 for the nineteenth century Italian composer Giuseppe Verdi. This crater, first imaged by Mariner 10, is an example of a complex crater, with a central peak structure and terraced walls.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

100 Orbits and Counting
MESSENGER Mission News | 2011 May 06
Later today, MESSENGER will begin its 100th orbit around Mercury. Since its insertion into orbit about the innermost planet on March 17, the spacecraft has executed nearly 2 million commands.

The data gathered so far include more than 70 million magnetic field measurements, 300,000 visible and infrared spectra of the surface, 16,000 images, and 12,000 X-ray and 9,000 gamma-ray spectra probing the elemental composition of Mercury’s uppermost crust.

“As the primary orbital phase of the MESSENGER mission unfolds, we are building up the first comprehensive view of the innermost planet,” states MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “The surface is unraveling before our eyes in great detail, and the planet’s topography and gravity and magnetic fields are being steadily filled in. As the Sun becomes increasingly active, Mercury’s extraordinarily dynamic exosphere and magnetosphere continue to display novel phenomena.”

MESSENGER continues its science-mapping phase in orbit around Mercury. All spacecraft systems remain safe and healthy, and all science instruments are on and continue to collect data according to the baseline observation plan.

“Over the next several weeks, MESSENGER’s subsystems and instruments will experience their hottest temperatures yet as the spacecraft crosses between the planet’s surface and our Sun at high noon close to the planet, preceded by hour-long eclipses near local midnight with only the spacecraft battery to keep the spacecraft alive in the dark of Mercury’s night,” notes MESSENGER Project Scientist Ralph McNutt.

“All of this was planned in great detail more than seven years ago, as was the orbit insertion burn that went so flawlessly,” he adds. “Theory is one thing and reality another, and the sense of thrill leading to ‘firsts’ is always followed by a sense of relief, especially in the challenging environment of interplanetary space, far from home.”

With less than one-sixth of its primary orbital mission completed, MESSENGER is already rewriting our books on what is known (and unknown) regarding the innermost planet, McNutt says. “By exploring our near — and far — neighbors in our solar system, we touch new knowledge, new understanding, and new wonderment about not only our own origins and place but of the other worlds circling the stars we see in our night sky.”
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 May 08-14

Post by bystander » Tue May 10, 2011 1:33 pm

A Rugged Landscape Outside of Caloris
NASA JHU-APL CIW | MESSENGER | 2011 May 09
This rough area of Mercury's surface is located outside of the large (1,550-kilometer diameter) Caloris basin. The formation of Caloris scoured the neighboring surface, creating the rugged landscape seen here.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Plains and Chains
NASA JHU-APL CIW | MESSENGER | 2011 May 10
The upper right portion of this image shows an area of smooth plains, while chains of secondary craters can be identified cutting across the middle of the image. This portion of Mercury's surface is located about 300 kilometers east of Verdi.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

The Crossing of Endeavour
NASA JHU-APL CIW | MESSENGER | 2011 May 11
The scarp (cliff) crossing vertically through this image is Endeavour Rupes, named for the ship used by Cook to explore Tahiti, New Zealand, and Australia in 1768-1771. Visit these images of Beagle Rupes and near the rim of Rembrandt to see examples of other scarps.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

South Pole - Take 15
NASA JHU-APL CIW | MESSENGER | 2011 May 12
This WAC image is shown in a polar stereographic projection, with the south pole at the center, 0° longitude at the top, and 90° E longitude to the right. The image extends to -70° latitude in all directions. This image is the 15th of 89 total WAC images planned in support of MDIS's south polar monitoring campaign.

One of MDIS's imaging campaigns is to monitor the south polar region of Mercury. By imaging the polar region every four MESSENGER orbits as illumination conditions change, features that were in shadow on earlier orbits can be discerned and any permanently shadowed areas can be identified after repeated imaging over one solar day. During MESSENGER's one-year mission, MDIS's WAC is used to monitor the south polar region for the first Mercury solar day (176 Earth days), and MDIS's NAC is used for imaging the south polar region during the second Mercury solar day.

Appreciating Mercury's Brahms
NASA JHU-APL CIW | MESSENGER | 2011 May 13
Mercury's Brahms crater is named for the nineteenth century German composer and pianist Johannes Brahms. Brahms is a complex crater with a central peak and terraced walls, like its neighbor Verdi. Smaller secondary craters are numerous in this scene and surround Brahms in all directions.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Science Highlights from Mercury’s Orbit

Post by bystander » Fri May 13, 2011 5:31 pm

The Imaging Campaigns of MESSENGER's Mercury Dual Imaging System
Science Highlights from Mercury’s Orbit | 2011 May 10
As the first spacecraft to orbit the planet Mercury, MESSENGER has the opportunity to make many observations of the Solar System's innermost planet that had not previously been possible. Each of MESSENGER’s eight science investigations has a one-year data collection plan that has been carefully designed to meet the goal of maximizing the science return for the mission. MESSENGER's Mercury Dual Imaging System (MDIS) is composed of two cameras, a wide-angle camera (WAC) and a narrow-angle camera (NAC). MDIS is scheduled to acquire more than 75,000 WAC and NAC images during the one-year orbital mission in support of MESSENGER's science goals. A range of imaging campaigns achieves a balance between globally mapping the entire surface of Mercury and obtaining targeted higher-resolution images in support of specific science goals. Together, MDIS's imaging campaigns will provide a new view of Mercury and will address one of the mission's main science questions: What is the geologic history of Mercury?
MDIS's Surface Morphology Base Map
During the first 176 days of the orbital mission, equal to one solar day on Mercury, MDIS will acquire images to produce a high-resolution base map for surface morphology (morphology is the term given to the shape and texture of the surface). This map will cover more than 90% of Mercury's surface at an average resolution of 250 m/pixel (0.16 miles/pixel or 820 feet/pixel) or better. At this resolution, features about 1 km in horizontal scale are recognizable in the images. Images acquired for the surface morphology base map have off-vertical solar illumination and visible shadows so as to reveal clearly the topographic form of geologic features. Because of MESSENGER's highly elliptical orbit, the spacecraft passes close to the surface at high northern latitudes but is far above the southern hemisphere, so both the NAC and the WAC are being used to construct the global base map. For the southern hemisphere, images are obtained with the NAC, which has a 1.5˚ field of view and can acquire images at seven times greater resolution than the WAC. For the northern hemisphere, when the spacecraft is closer to and moving faster over the surface, the WAC is used, because its 10.5° field of view enables good image coverage. Images from both the NAC and the WAC will be mosaicked together to produce the global map. Shown here is an example mosaic of four images acquired as part of the surface morphology campaign. The large crater in the center is Valmiki (210 km diameter).
Mapping Mercury's Surface in Color
In addition to the surface morphology base map, MDIS is currently acquiring a color base map during the mission's first 176 days. The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface at an average resolution of 1 km/pixel (0.6 miles/pixel) or better. In contrast to the imaging conditions best suited for seeing surface topography, the highest-quality color images of Mercury's surface are obtained when both the spacecraft and the Sun are overhead and shadows are limited. The eight different color filters of the WAC that are used to create the color base map have central wavelengths of 430, 480, 560, 630, 750, 830, 900, and 1000 nm. The images acquired through these narrow-band filters are combined to create color images that accentuate color differences on Mercury's surface. As an example, the image in Figure 2 was created by using three images acquired as part of the color base map with the central wavelengths of 1000, 750, and 430 nm displayed in red, green, and blue, respectively.

After the surface morphology base map is acquired during the first Mercury solar day, a second, complementary near-global map, called the stereo base map, will be acquired during the second Mercury solar day of MESSENGER’s one-year orbital mission. The stereo base map will be used in combination with the surface morphology base map to create high-resolution stereo views of Mercury's surface at an average resolution of 250 m/pixel (0.16 miles/pixel or 820 feet/pixel) or better. As with the surface morphology base map, images are acquired under non-vertical solar illumination, so that shadows accentuate the topography of the surface. In addition, the stereo basemap images are acquired under viewing angles that differ from those for the morphology base map by about 20°, allowing stereo information about the surface to be determined. As the mission is currently in the first Mercury solar day, no images have yet been acquired in support of the stereo base map. However, different viewing conditions during MESSENGER's second and third Mercury flybys allowed stereo information to be obtained for a portion of Mercury's surface at an image resolution of 500 m/pixel. View this example of Rembrandt to see the type of stereo data that will be derived from the two sets of image base maps.
Monitoring Mercury's South Pole

In addition to the three global base maps, there is an MDIS imaging campaign to monitor the south polar region of Mercury. By imaging the south polar region once every four MESSENGER orbits (once every two Earth days) as illumination conditions change, features that were in shadow on earlier orbits can be discerned and any permanently shadowed areas can be identified over one Mercury solar day. Identifying areas of permanent shadow are of interest to understand the unusual materials at Mercury's poles and whether these highly radar-reflective materials consist of water ice. During MESSENGER's one-year mission, the WAC is used to monitor the polar region south of 70°S at 1.5 km/pixel for the first Mercury solar day. On the second Mercury solar day, the NAC will be used for imaging the polar region south of 85°S at 300 m/pixel. An example WAC image acquired as part of MDIS's south polar monitoring campaign is shown here.
Weekly Limb Imaging

Once per week, MDIS captures images of Mercury's limb (the edge of the sunlit planet with space), with an emphasis on imaging the southern hemisphere limb. An example of one of those limb images is shown here. The spacecraft was high above Mercury's south polar region when capturing this image. However, even when the spacecraft is at its highest altitude above Mercury, a single WAC image cannot capture the entire limb of Mercury. Consequently, two images are taken and mosaicked together to image Mercury's entire limb. These limb images will provide information about Mercury's shape and will complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.
Targeted Observations Reveal Unprecedented Detail

MDIS acquires targeted images of small areas on Mercury's surface at resolutions much higher than those of the morphology, stereo, or color base maps. It is not possible to cover all of Mercury's surface at such high resolutions during MESSENGER’s one-year primary mission, but several areas of high scientific interest are generally imaged in this mode each week. Additionally, as new features of particular science interest are imaged from orbit, targets are added to a database list and will be imaged if possible at higher resolution by MDIS, or with multiple instruments, the next time that area of Mercury is in view from the spacecraft. This image is a mosaic of four images from a targeted observation acquired at 15 m/pixel, a resolution that is more than an order of magnitude improvement over the surface morphology base map. These ultra-high-resolution images are revealing Mercury's surface in unprecedented detail.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 May 15-21

Post by bystander » Mon May 16, 2011 4:10 pm

Another Look at Atget
NASA JHU-APL CIW | MESSENGER | 2011 May 16
At a diameter of 100 km, the crater Atget is one of the largest craters within the Caloris basin. This targeted NAC observation provides our first high-resolution view of Atget's low-reflectance floor and ejecta, which were likely excavated from beneath the surficial plains when Atget formed. Check out Atget in this enhanced color view of Caloris; it's the dark blue crater just south of Caloris's center.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

The Caloris Montes
NASA JHU-APL CIW | MESSENGER | 2011 May 17
The Caloris Montes are the ring of mountainous peaks that make up the rim of the Caloris basin. Shown here is the southeastern portion of the rim, first seen by Mariner 10. This month MESSENGER is getting its first orbital look at Caloris, and its first images of the basin with the Sun low in the sky (high incidence angles), allowing for unprecedented views of the topographic features of one of the largest basins in the Solar System.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Basins Everywhere
NASA JHU-APL CIW | MESSENGER | 2011 May 18
An unnamed basin, largely filled with smooth plains, occupies most of this WAC image. The oblique look at this basin highlights the more rugged and cratered terrain exterior to the basin.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Ring Around the Basin
NASA JHU-APL CIW | MESSENGER | 2011 May 19
Mercury is covered with beautiful peak-ring basins, and a slice of one can be seen here. In fact, though this peak-ring basin was seen during MESSENGER's second flyby of Mercury, it does not yet have a name.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Looking up from the South
NASA JHU-APL CIW | MESSENGER | 2011 May 20
This view from the south highlights the rayed crater Han Kan (50 km), just to the north of Van Gogh (100 km). This image, acquired on May 17, 2011, gives a great sense of MESSENGER's elliptical orbit, where the spacecraft spends most of its time relatively far from the planet. Check out MESSENGER's current location!

This image was acquired as part of MDIS's limb imaging campaign. Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb. These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Science Highlights from Mercury Orbit

Post by bystander » Fri May 20, 2011 9:47 pm

Measuring Mercury's Magnetic Field
Science Highlights from Mercury Orbit | 2011 May 17
MESSENGER carries a sensitive Magnetometer that measures the vector magnetic field at the location of the spacecraft. The instrument is mounted on the end of a 3.6-m-long boom that extends away from the spacecraft in the direction opposite to the sunshade (Figure 1). The Magnetometer works like a three-axis compass that determines how strong the magnetic field is in all three directions and specifies the direction and strength of the magnetic field at every point in MESSENGER’s orbit around the planet. Since the first encounter of the Mariner 10 spacecraft with Mercury in 1974, we have known that Mercury has an internal magnetic field with a strength at the surface that is about 1% as strong as at Earth. The MESSENGER Magnetometer is a high-precision instrument that can sense fields only one millionth as strong as the field at the surface of the Earth, so magnetic signals that are only a tiny fraction of the maximum magnetic field at Mercury can be characterized. The global structure of Mercury’s magnetic field will be determined by combining data taken from all of MESSENGER’s orbits about the planet.

Planetary Magnetic Fields

Venus and Mars are the only planets in our solar system that do not have global planetary magnetic fields. Mercury is particularly interesting because its magnetic field is weak compared to those of the other planets. Planetary magnetic fields arise not because the planets contain giant permanent magnets, but because at least some portion of their interiors is fluid and electrically conductive. In Earth and in Mercury, that fluid is the molten iron of the planet’s outer core (Figure 2). As the core cools, molten material solidifies and heat is released. This heat can stir the remaining molten material to ciruclate much as boiling water circulates in a heated pot. The circulation of the molten outer cores amplifies any magnetic field present in the material and converts a small fraction of the energy of motion into a magnetic field, a process known as a magnetic dynamo. When the core cools sufficiently to become completely solid, or when the stirring action in the outer core becomes sufficiently weak, the dynamo stops, and the only remaining field is that of material in the planet’s outer crust that was permanently magnetized during the operation of the dynamo. Planetary magnetic fields therefore provide insight into past and current processes deep within the planet.

Why Does Mercury Have a Magnetic Field?

Of the rocky planets (Mercury, Venus, Earth, and Mars), Mercury is the smallest and Earth the largest. Because neither Venus nor Mars has a global magnetic field (although Mars has magnetized crust) it had been thought that Mercury would have no global field. Contrary to these expectations, Mariner 10 observations showed that Mercury indeed has a global field, albeit a weak one, and it has since been a challenge to understand how this field can have persisted over the lifetime of the planet. The leading hypothesis is that at least an outer shell of the core remains molten because it contains a lighter element as well as Iron, and the lighter element is present in sufficient abundance to lower the freezing point of the alloy, much as salt added to water lowers the freezing point of the mixture below that of pure water. Numerical simulations have shown that even a thin molten shell could support a dynamo and create the magnetic field seen today at Mercury, but many details of the process are uncertain. Deducing the origin of Mercury’s magnetic field is one of the central goals of the MESSENGER mission, and the Magnetometer is providing key data to address this question.

Complications of a Weak Magnetic Field

As at Earth, Mercury’s magnetic field is immersed in the solar wind and the interplanetary magnetic field (Figure 3). At Earth the interactions between the magnetic field and the solar wind generate the spectacular aurora in the polar regions and are responsible for the Van Allen radiation belts. Because Earth’s magnetic field is comparatively strong, the solar wind does not change the magnetic field very much at ground level. It is for this reason that one can reliably use compasses for navigation. At Mercury however, the situation is quite different. Not only is the planetary magnetic field much weaker than Earth’s, but because Mercury is much closer to the Sun the solar wind is approximately ten times stronger. As a result the effect of the solar wind is about 1,000 times greater at Mercury and the volume over which Mercury’s magnetic field “shields” the planet, known as the magnetosphere, is comparably tiny. It extends only 40% of the planet’s radius toward the Sun, and the distortion of the magnetic field close to the surface is nearly as strong as the planet’s own magnetic field. To understand Mercury’s magnetic field, it is therefore essential to understand the interaction of that field with the solar wind.

MESSENGER's Magnetic Mapping Program

Because the magnetic field carried by the solar wind that flows around Mercury’s magnetic field interacts strongly with the magnetic field of the planet, an extensive campaign in which we map out the magnetic field everywhere around the planet is required to separate the internal field of the planet from other fields. By taking data continuously, throughout the entire year of observations, the Magnetometer will collect more than 500 million measurements (Figure 4). Because the observations reach as close as 200 km from the surface – well within Mercury’s magnetosphere – and as far as 15,000 km – within the solar wind itself – the data will allow mapping of the magnetosphere’s boundaries, measurement of the currents along those boundaries, and separation of the internal magnetic field from these “external” sources to understand the dynamic processes that give rise to the planet’s magnetism.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: 2011 May 22-28

Post by bystander » Mon May 23, 2011 4:13 pm

Rock Lobster
NASA JHU-APL CIW | MESSENGER | 2011 May 23
The central peak of this 34-km diameter crater vaguely resembles a lobster's claw. South is to the top in this presentation. The very smooth parts of the floor may be ponded impact melt. King crater on the Moon also has a famous lobster-claw central peak.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Been Up on Abedin's Terrace
NASA JHU-APL CIW | MESSENGER | 2011 May 24
This image shows the southeast quadrant of the crater Abedin. We saw the northeast section of this 110–km (68-mi.) diameter crater in a previous Gallery release. Here we draw attention to the wall terraces on the southern rim, formed by landslides when portions of the walls collapsed into the crater cavity.

This image was acquired as part of MDIS's color base map. The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface with an average resolution of 1 kilometer/pixel (0.6 miles/pixel). The highest-quality color images are obtained for Mercury's surface when both the spacecraft and the Sun are overhead, so these images typically are taken with viewing conditions of low incidence and emission angles.

We Are Glass
NASA JHU-APL CIW | MESSENGER | 2011 May 25
This high-resolution view depicts an area of the surface north of the crater Geddes. The surface here has not been greatly disturbed by crater rays or recent secondary crater impacts, events that can deposit or excavate crystalline bedrock. However, the area has not escaped the prolonged action of micrometeoroid bombardment, which has likely converted much of the soil to a glassy state.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

A Hard Rain's A-Gonna Fall
NASA JHU-APL CIW | MESSENGER | 2011 May 26
This view of Mercury's surface reveals an abundance of subdued craters that are about 5 km in diameter. These are probably old secondary craters, formed as large chunks ejected by a basin impact fell as a pummeling rain.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Twin Peaks
NASA JHU-APL CIW | MESSENGER | 2011 May 27
MESSENGER captured this view of a medium-sized crater that formed in a smooth plains unit. A cleft has formed in the central peak, producing two mountains of nearly identical size.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Science Highlights from Mercury Orbit

Post by bystander » Fri May 27, 2011 7:34 am

Altimetry Is Defining Mercury's Shape
Science Highlights from Mercury Orbit | 2011 May 24
MESSENGER’s Mercury Laser Altimeter (MLA) in its first 2 months of operation has already built up a grid of ground tracks that span most of Mercury’s surface north of the equator (Figure 1). These data will provide a very good measure of the shape of the planet’s northern hemisphere. The shape of a planet carries a record of all of the interior dynamical and geological processes that have modified the surface.

Signals from MLA’s laser reflected from the surface can be recovered whenever the spacecraft is within a range of about 1,800 km (about 1,100 miles) from the ground track. Because of MESSENGER’s highly elliptical orbit, MLA can make measurements only for a portion of each orbit approximately centered on closest approach (Figure 2). By far the most accurate instrument on MESSENGER for determining the shape of Mercury, MLA is yielding precise topographic measurements of Mercury’s northern hemisphere, but other techniques must be employed to measure the shape of the southern hemisphere. These complementary techniques include the creation of three-dimensional terrain models from stereo images obtained with MESSENGER’s Mercury Dual Imaging System (MDIS), radio occultations, and MDIS profiling of the planet’s limb.

The MESSENGER spacecraft conducts stereo imaging by photographing regions of Mercury’s surface at more than one viewing geometry. The first step in the conversion of stereo images to topographic models is to identify common points in each image of a given area. Then, for each image a line of sight can be constructed from the camera location to each common point. The intersection of the lines of sight to a given common point from two viewing geometries constrains the position of the point on the surface of a topographic model. With many common points, one can reconstruct the shape of the area imaged.

Radio occultations provide an independent means to measure the shape of the planet. Occultations occur when the planet blocks radio waves sent from the MESSENGER spacecraft to Earth. By measuring carefully the times of disappearance or appearance of the radio signal at the beginning or end of an occultation, the science team can determine the local radius of the planet.

The shape of Mercury’s southern hemisphere can also be determined by capturing images of the planet’s limb (the outer edge of the sunlit planet) with MDIS. Limb imaging allows the shape of the surface to be seen because of the contrast between the bright edge of the planet and the darkness of space.

Because the MLA data are highly accurate, they can be used to “calibrate” data obtained by other techniques. For example, in Mercury’s northern hemisphere, a precise measurement from MLA can be used to fix portions of a topographic map created from stereo imaging or to sharpen estimates of local radius obtained from occultations or limb profiling. Such results can then be extrapolated to the southern hemisphere, where MLA data are not available.

By combining stereo-derived topographic models, radio occultation measurements, and limb profiles with MLA observations, the MESSENGER science team will determine accurately the global shape of Mercury.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Belinskij and Craters of Darkness

Post by bystander » Mon May 30, 2011 5:01 am

Belinskij and Craters of Darkness
NASA JHU-APL CIW | MESSENGER | 2011 May 30
The largest crater in this scene, located in the upper left portion of the image, is Belinskij, named for the Russian literary critic and journalist Vissarion Grigoryevich Belinskij (1811-1848). The crater to the east of Belinskij and about half its size contains radar-bright material. This material may be water ice, present due to low temperature conditions within a permanently shadowed region of this crater. MDIS's south polar imaging campaign will determine which of Mercury's craters contain areas of permanent shadow.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Brights Rays, Small Crater

Post by bystander » Tue May 31, 2011 4:10 pm

Brights Rays, Small Crater
NASA JHU-APL CIW | MESSENGER | 2011 May 31
The crater Han Kan, with a diameter of 50 kilometers, is far from the largest crater in this scene, but its bright rays make it stand out from its many larger neighbors. View Mercury in Google Earth to identify Han Kan's neighbors, including the double-ring basins Bach and Cervantes.

This image was acquired as part of MDIS's color base map. The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface with an average resolution of 1 kilometer/pixel (0.6 miles/pixel). The highest-quality color images are obtained for Mercury's surface when both the spacecraft and the Sun are overhead, so these images typically are taken with viewing conditions of low incidence and emission angles.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Gazing Over a Cratered World

Post by bystander » Wed Jun 01, 2011 3:39 pm

Gazing Over a Cratered World
NASA JHU-APL CIW | MESSENGER | 2011 Jun 01
This striking image was acquired as MDIS used its pivot to look toward the southeast, which is oriented as the top of the image. This rough, cratered landscape is located north of the basin shown here.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Crescent View of Mercury

Post by bystander » Fri Jun 03, 2011 2:42 pm

Crescent View of Mercury
NASA JHU-APL CIW | MESSENGER | 2011 Jun 02
Mercury forms a beautiful crescent shape in this image, acquired as the MESSENGER spacecraft was high above Mercury's southern hemisphere. On the left side is the terminator, dividing the day from night. On the right side is the sunlit limb, separating Mercury from the darkness of space.

This image was acquired as part of MDIS's limb imaging campaign. Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb. These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: The Rim of Cervantes

Post by bystander » Fri Jun 03, 2011 2:47 pm

The Rim of Cervantes
NASA JHU-APL CIW | MESSENGER | 2011 Jun 03
The rim of the double-ring basin Cervantes cuts through the middle of this NAC image. Cervantes has a diameter of 213 kilometers and was named in honor of the Spanish novelist, playwright, and poet Miguel de Cervantes (1547-1616), best known for his novel Don Quixote.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Revealing More Northern Terrain

Post by bystander » Mon Jun 06, 2011 2:48 pm

Revealing More Northern Terrain
NASA JHU-APL CIW | MESSENGER | 2011 Jun 06
This image reveals previously unseen terrain near Mercury's north pole. There is a sharp boundary between smooth and rough terrain, but without seeing the neighboring areas, the boundary is difficult to interpret. Mosaicking this image with surrounding images will allow MESSENGER scientists to understand the geology of this region.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Crater Degradation

Post by bystander » Tue Jun 07, 2011 1:48 pm

Crater Degradation
NASA JHU-APL CIW | MESSENGER | 2011 Jun 07
The craters in this scene span a variety of degradation states. The sharp-looking crater near the center of the image has not undergone significant infilling or degradation, unlike the larger craters to the south. Its appearance indicates that it is relatively younger than these larger craters.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 21576
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

MESSENGER: Wall Slumps

Post by bystander » Wed Jun 08, 2011 2:58 pm

Wall Slumps
NASA JHU-APL CIW | MESSENGER | 2011 Jun 08
This high-resolution image of a crater wall shows several slumps that occurred after the 20-km-diameter crater formed. The bottom-right corner of this image is located inside of the crater, and the upper-left corner is located outside of the crater rim.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor