Dawn: Journey to the Asteroid Belt

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Dawn: Journey to the Asteroid Belt

Postby bystander » Wed May 11, 2011 5:22 pm

Dawn Captures First Image of Nearing Asteroid
NASA JPL-Caltech Dawn | 2011 May 11
Dawn's First Glimpse of Vesta
(Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
NASA's Dawn spacecraft has obtained its first image of the giant asteroid Vesta, which will help fine-tune navigation during its approach. Dawn is expected to achieve orbit around Vesta on July 16, when the asteroid is about 188 million kilometers (117 million miles) from Earth.

The image from Dawn's framing cameras was taken on May 3 when the spacecraft began its approach and was approximately 1.21 million kilometers (752,000 miles) from Vesta. The asteroid appears as a small, bright pearl against a background of stars. Vesta is also known as a protoplanet, because it is a large body that almost formed into a planet.

"After plying the seas of space for more than a billion miles, the Dawn team finally spotted its target," said Carol Raymond, Dawn's deputy principal investigator at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This first image hints of detailed portraits to come from Dawn's upcoming visit."

Vesta is 530 kilometers (330 miles) in diameter and the second most massive object in the asteroid belt. Ground- and space-based telescopes obtained images of the bright orb for about two centuries, but with little surface detail.

Mission managers expect Vesta's gravity to capture Dawn in orbit on July 16. To enter orbit, Dawn must match the asteroid's path around the sun, which requires very precise knowledge of the body's location and speed. By analyzing where Vesta appears relative to stars in framing camera images, navigators will pin down its location and enable engineers to refine the spacecraft's trajectory.

Dawn will start collecting science data in early August at an altitude of approximately 1,700 miles (2,700 kilometers) above the asteroid's surface. As the spacecraft gets closer, it will snap multi-angle images, allowing scientists to produce topographic maps. Dawn will later orbit at approximately 200 kilometers (120 miles) to perform other measurements and obtain closer shots of parts of the surface. Dawn will remain in orbit around Vesta for one year. After another long cruise phase, Dawn will arrive in 2015 at its second destination, Ceres, an even more massive body in the asteroid belt.

Gathering information about these two icons of the asteroid belt will help scientists unlock the secrets of our solar system's early history. The mission will compare and contrast the two giant bodies shaped by different forces. Dawn's science instruments will measure surface composition, topography and texture. Dawn will also measure the tug of gravity from Vesta and Ceres to learn more about their internal structures. The spacecraft's full odyssey will take it on a 5-billion-kilometer (3-billion-mile) journey, which began with its launch in September 2007.

Dawn Mission Page
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Re: JPL: Dawn Captures First Image of Nearing Asteroid

Postby alter-ego » Tue May 24, 2011 6:44 am

I would've submitted this earlier but I missed this topic. Below the three brightest stars are identified:

Vesta Picture from Dawn, 11 May 2011.jpg

With a bit of luck, you might be able to identify a simulated star background star field at the Dawn website combined with the JPL Solar System Simulator, or you can submit the picture to the Astrometry.net pool and they'll identify it for you (I haven't tried this yet).

I was drawn to the challenge of identifying the background field on my own. Dawn's framing camera 5.5º field-of-view makes guessing this field seemingly impossible, but using the JPL Horizons Ephemeris tool to retrieve and analyze the rectangular coordinate position data (relative or absolute) for Vesta and Dawn made it possible, and surprisingly accurate. Some trignonometry applied to the data directly correlates to the ecliptical coordinate system. So the line-of-site "pointing vector" from Dawn to Vesta is the difference in the X,Y,Z coordinates of the two objects, and this vector points to Vesta's celestial coordinates as viewed from Dawn. I looked a Horizons' data over many days, but picked the stated date of May 3rd as the date of the photo.

My result? I calculated Vesta's coordinates as viewed from Dawn to <1º position error from the pictured position. The prediction is so close that I don't think I made any mistakes, or I was lucky. The Horizons ephemeris tells the Dawn approach story and it all makes sense!
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UCLA: Dawn spacecraft approaches protoplanet Vesta

Postby bystander » Sun Jun 12, 2011 12:09 am

Dawn spacecraft approaches protoplanet Vesta
University of California, Los Angeles | 2011 Jun 10
The 'moment of truth is about to arrive,' says UCLA's Christopher Russell

NASA's Dawn mission to the doughnut-shaped asteroid belt between Mars and Jupiter, which launched in September 2007, is now approaching Vesta, a protoplanet that is currently some 143 million miles from Earth. Many surprises are likely awaiting the spacecraft.

"We often refer to Vesta as the smallest terrestrial planet," said Christopher T. Russell, a UCLA professor of geophysics and space physics in the Department of Earth and Space Sciences, and the mission's principal investigator. "It has planetary features and basically the same structure as Mercury, Venus, Earth and Mars. But because it is so small, it does not have enough gravity to retain an atmosphere, or at least not to retain an atmosphere for very long.

"There are many mysteries about Vesta," Russell said. "One of them is why Vesta is so bright. The Earth reflects a lot of sunlight — about 40 percent — because it has clouds and snow on the surface, while the moon reflects only about 10 percent of the light from the sun back. Vesta is more like the Earth. Why? What on its surface is causing all that sunlight to be reflected? We'll find out."

Dawn will map Vesta's surface, which Russell says may be similar to the moon's. He says he expects that the body's interior is layered, with a crust, a mantle and an iron core. He is eager to learn about this interior and how large the iron core is.

Named for the ancient Roman goddess of the hearth, Vesta has been bombarded by meteorites for 4.5 billion years.

"We expect to see a lot of craters," Russell said. "We know there is an enormous crater at the south pole that we can see with the Hubble Space Telescope. That crater, some 280 miles across, has released material into the asteroid belt. Small bits of Vesta are floating around and make their way all the way to the orbit of the Earth and fall in our atmosphere. About one in every 20 meteorites that falls on the surface of the Earth comes from Vesta. That has enabled us to learn a lot about Vesta before we even get there."

Dawn will arrive at Vesta in July. Beginning in September, the spacecraft will orbit Vesta some 400 miles from its surface. It will then move closer, to about 125 miles from the surface, starting in November. By January of 2012, Russell expects high-resolution images and other data about surface composition. Dawn is arriving ahead of schedule and is expected to orbit Vesta for a year.

"It's been a long trip," said Russell, who started planning the journey back in 1992. "Finally, the moment of truth is about to arrive."

Vesta, which orbits the sun every 3.6 terrestrial years, has an oval, pumpkin-like shape and an average diameter of approximately 330 miles. Studies of meteorites found on Earth that are believed to have come from Vesta suggest that Vesta formed from galactic dust during the solar system's first 3 million to 10 million years.

Dawn's cameras should be able to see individual lava flows and craters tens of feet across on Vesta's surface.

"We will scurry around when the data come in, trying to make maps of the surface and learning its exact shape and size," Russell said.

Dawn has a high-quality camera, along with a back-up; a visible and near-infrared spectrometer that will identify minerals on the surface; and a gamma ray and neutron spectrometer that will reveal the abundance of elements such as iron and hydrogen, possibly from water, in the soil. Dawn will also probe Vesta's gravity with radio signals.

The study of Vesta, however, is only half of Dawn's mission. The spacecraft will also conduct a detailed study of the structure and composition of the "dwarf planet" Ceres. Vesta and Ceres are the most massive objects in the main asteroid belt between Mars and Jupiter. Dawn's goals include determining the shape, size, composition, internal structure, and the tectonic and thermal evolution of both objects, and the mission is expected to reveal the conditions under which each of them formed.

Dawn, only the second scientific mission to be powered by an advanced NASA technology known as ion propulsion, is also the first NASA mission to orbit two major objects.

"Twice the bang for the buck on this mission," said Russell, who added that without ion propulsion, Dawn would have cost three times as much.

Unlike chemical rocket engines, ion engines accelerate their fuel nearly continuously, giving each ion a tremendous burst of speed. The fuel used by an ion engine is xenon, a gas that is also used in photo-flash units and which is more than four times heavier than air. Xenon ions shoot out the back of the engine at a speed of 90,000 miles per hour.

UCLA graduate and postdoctoral students work with Russell on the mission. Now is an excellent opportunity for graduate students to join the project and help analyze the data, said Russell, who teaches planetary science to UCLA undergraduates and solar and space physics to undergraduates and graduate students.

After orbiting Vesta, Dawn will leave for its three-year journey to Ceres, which could harbor substantial water or ice beneath its rock crust — and possibly life. On the way to Ceres, Dawn may visit another object. The spacecraft will rendezvous with Ceres and begin orbiting in 2015, conducting studies and observations for at least five months.

Russell believes that Ceres and Vesta, formed almost 4.6 billion years ago, have preserved their early record, which was frozen into their ancient surfaces.

"We're going back in time to the early solar system," he said.
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Dawn's Early Light

Postby neufer » Mon Jun 13, 2011 6:01 pm

http://dawn.jpl.nasa.gov/feature_storie ... _video.asp wrote:
NASA Spacecraft Captures Video of Asteroid Approach

Click to play embedded YouTube video.

June 13, 2011 - PASADENA, Calif. -- <<Scientists working with NASA's Dawn spacecraft have created a new video showing the giant asteroid Vesta as the spacecraft approaches this unexplored world in the main asteroid belt. The video loops 20 images obtained for navigation purposes on June 1. The images show a dark feature near Vesta's equator moving from left to right across the field of view as Vesta rotates. Images also show Vesta's jagged, irregular shape, hinting at the enormous crater known to exist at Vesta's south pole.

The images were obtained by a framing camera during a 30-minute period and show about 30 degrees of a rotation. The pixel size in these images is approaching the resolution of the best Hubble Space Telescope images of Vesta.

"Like strangers in a strange land, we're looking for familiar landmarks," said Jian-Yang Li, a Dawn participating scientist from the University of Maryland, College Park. "The shadowy spot is one of those -- it appears to match a feature, known as 'Feature B,' from images of Vesta taken by NASA's Hubble Space Telescope."

Before orbiting Vesta on July 16, Dawn will gently slow down to about 75 mph (120 kilometers per hour). NASA is expecting to release more images on a weekly basis, with more frequent images available once the spacecraft begins collecting science at Vesta.

"Vesta is coming more and more into focus," said Andreas Nathues, framing camera lead investigator, based at the Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany. "Dawn's framing camera is working exactly as anticipated."

The Dawn mission is managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., for the agency's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed and built the Dawn spacecraft. The framing cameras were developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germay. The German Aerospace Center (DLR) Institute of Planetary Research in Berlin made significant contributions in coordination with the Institute of Computer and Communication Network Engineering in Braunschweig. The framing camera project is funded by the Max Planck Society, DLR and NASA. JPL is a division of the California Institute of Technology in Pasadena.

For more information about Dawn, visit: http://www.nasa.gov/dawn. You can follow the mission on Twitter at: http://twitter.com/NASA_Dawn.

More information about JPL is online at: http://www.jpl.nasa.gov.

The video from Dawn also will air Monday afternoon on NASA Television's Video File. For NASA TV downlink information, schedules and links to streaming video, visit: http://www.nasa.gov/ntv. >>
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Dawn Nears Start of Year-Long Stay at Giant Asteroid

Postby bystander » Fri Jun 24, 2011 5:32 am

Dawn Nears Start of Year-Long Stay at Giant Asteroid
NASA JPL-Caltech | Dawn Mission Page | 2011 June 23
Click to play embedded YouTube video.

Click to play embedded YouTube video.

Vesta in Spectrometer View
Credit: NASA/JPL-Caltech/UCLA/ASI/INAF
NASA's Dawn spacecraft is on track to begin the first extended visit to a large asteroid. The mission expects to go into orbit around Vesta on July 16 and begin gathering science data in early August. Vesta resides in the main asteroid belt and is thought to be the source of a large number of meteorites that fall to Earth.

"The spacecraft is right on target," said Robert Mase, Dawn project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. "We look forward to exploring this unknown world during Dawn's one-year stay in Vesta's orbit."

After traveling nearly four years and 1.7 billion miles (2.7 billion kilometers), Dawn is approximately 96,000 miles (155,000 kilometers) away from Vesta. When Vesta captures Dawn into its orbit on July 16, there will be approximately 9,900 miles (16,000 kilometers) between them. When orbit is achieved, they will be approximately 117 million miles (188 million kilometers) away from Earth.

After Dawn enters Vesta's orbit, engineers will need a few days to determine the exact time of capture. Unlike other missions where a dramatic, nail-biting propulsive burn results in orbit insertion around a planet, Dawn has been using its placid ion propulsion system to subtly shape its path for years to match Vesta's orbit around the sun.

Images from Dawn's framing camera, taken for navigation purposes, show the slow progress toward Vesta. They also show Vesta rotating about 65 degrees in the field of view. The images are about twice as sharp as the best images of Vesta from NASA's Hubble Space Telescope, but the surface details Dawn will obtain are still a mystery.

"Navigation images from Dawn's framing camera have given us intriguing hints of Vesta, but we're looking forward to the heart of Vesta operations, when we begin officially collecting science data," said Christopher Russell, Dawn principal investigator, at UCLA. "We can't wait for Dawn to peel back the layers of time and reveal the early history of our solar system."

Dawn's three instruments are all functioning and appear to be properly calibrated. The visible and infrared mapping spectrometer, for example, has started to obtain images of Vesta that are larger than a few pixels in size. During the initial reconnaissance orbit, at approximately 1,700 miles (2,700 kilometers), the spacecraft will get a broad overview of Vesta with color pictures and data in different wavelengths of reflected light. The spacecraft will move into a high-altitude mapping orbit, about 420 miles (680 kilometers) above the surface to systematically map the parts of Vesta's surface illuminated by the sun; collect stereo images to see topographic highs and lows; acquire higher-resolution data to map rock types at the surface; and learn more about Vesta's thermal properties.

Dawn then will move even closer, to a low-altitude mapping orbit approximately 120 miles (200 kilometers) above the surface. The primary science goals of this orbit are to detect the byproducts of cosmic rays hitting the surface and help scientists determine the many kinds of atoms there, and probe the protoplanet's internal structure. As Dawn spirals away from Vesta, it will pause again at the high-altitude mapping orbit. Because the sun's angle on the surface will have progressed, scientists will be able to see previously hidden terrain while obtaining different views of surface features.

"We've packed our year at Vesta chock-full of science observations to help us unravel the mysteries of Vesta," said Carol Raymond, Dawn's deputy principal investigator at JPL. Vesta is considered a protoplanet, or body that never quite became a full-fledged planet.

Dawn launched in September 2007. Following a year at Vesta, the spacecraft will depart for its second destination, the dwarf planet Ceres, in July 2012. Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala.

Dawn News Conference Press Materials

NASA Probe on Target for Asteroid Encounter Next Month
Space.com |Mike Wall | 2011 June 23

Dawn Closing In on Asteroid Vesta
Science Shot | Richard A Kerr | 2011 June 23

Vesta looks pretty battered
Planetary Society | Emily Lakdawalla | 2011 June 23

Amateur takes on the Dawn Vesta images
Planetary Society | Emily Lakdawalla | 2011 June 24
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Re: JPL: Dawn Captures First Image of Nearing Asteroid

Postby neufer » Fri Jul 08, 2011 7:12 pm

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NASA: Dawn Enters Orbit Around Vesta

Postby bystander » Sun Jul 17, 2011 5:26 pm

Dawn Spacecraft Enters Orbit Around Asteroid Vesta
NASA JPL-Caltech Dawn | 2011 July 16
NASA's Dawn spacecraft on Saturday became the first probe ever to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

Dawn will study the asteroid, named Vesta, for a year before departing for a second destination, a dwarf planet named Ceres, in July 2012. Observations will provide unprecedented data to help scientists understand the earliest chapter of our solar system. The data also will help pave the way for future human space missions.

"Today, we celebrate an incredible exploration milestone as a spacecraft enters orbit around an object in the main asteroid belt for the first time," NASA Administrator Charles Bolden said. "Dawn's study of the asteroid Vesta marks a major scientific accomplishment and also points the way to the future destinations where people will travel in the coming years. President Obama has directed NASA to send astronauts to an asteroid by 2025, and Dawn is gathering crucial data that will inform that mission."

The spacecraft relayed information to confirm it entered Vesta's orbit, but the precise time this milestone occurred is unknown at this time. The time of Dawn's capture depended on Vesta's mass and gravity, which only has been estimated until now. The asteroid's mass determines the strength of its gravitational pull. If Vesta is more massive, its gravity is stronger, meaning it pulled Dawn into orbit sooner. If the asteroid is less massive, its gravity is weaker and it would have taken the spacecraft longer to achieve orbit. With Dawn now in orbit, the science team can take more accurate measurements of Vesta's gravity and gather more accurate timeline information.

Dawn, which launched in September 2007, is on track to become the first spacecraft to orbit two solar system destinations beyond Earth. ...

Dawn Mission Page (NASA)
Dawn Mission Page (JPL-Caltech)

NASA Spacecraft Enters Orbit Around Asteroid Vesta — A Space First
Space.com | Tariq Malik | 2011 July 17

Confirmed! Dawn is Orbiting Asteroid Vesta
Discovery Space News | Ian O'Neill | 2011 July 17
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Re: JPL: Dawn Captures First Image of Nearing Asteroid

Postby neufer » Tue Jul 19, 2011 1:35 am

http://www.planetary.org/blog/article/00003104/ wrote:
Yet another new image of Vesta
The Planetary Society Blog
By Emily Lakdawalla | Jul. 18, 2011

<<A sharp-eyed reader noticed that a size comparison montage posted by the Dawn mission today included an image of Vesta that had not yet been released separately to the public, and it is a very cool one. It was taken at a different time of the Vestian day, with slightly more oblique lighting, and is very dramatic. Now that ridgy floor and central peak of the south polar impact basin look like a gigantic bug, or maybe a crab.

There's a new orbital mission on the map! As of Friday, the relatively small mass of the asteroid Vesta (it only weighs half a ten thousandth of Earth's mass) has finally taken hold of its new artificial satellite, Dawn. But that's a tenuous grip, so for the next three weeks Dawn will continue applying its ion engines to tighten the orbit, spiraling inward from its orbit capture altitude of 16,000 kilometers until it has reached an altitude of 2,700 kilometers. Only then will Dawn officially be in Survey Orbit.

This announcement came on Friday but I was hoping they'd release a new image from the new altitude, and today they finally did. Here it is, and it's a very pretty one, though there are some peculiarities I'll mention below. With this latest image Vesta has become, to me, a place -- no longer an imagined object, but a real one.

The interior of that south polar basin sure looks weird. All around the central peak are chevron-shaped ridgy features that bring to mind Miranda -- which, by the way, is very similar in size to Vesta. Such an unusual terrain, located preferentially within the interior of this gigantic crater, must have something to do with how the crater formed, at least that's the way I see it. I'm looking forward to seeing what this terrain looks like at higher resolution as Dawn spirals downward.

In the outer solar system, bodies about 500 kilometers across tend toward round shapes. In the asteroid belt, things are different: rocky Vesta, which is much larger than these icy moons, is noticeably lumpy. Credit: NASA / JPL / SSI / UCLA / MPS / DLR / IDA processing by Gordan Ugarkovic (Enceladus, Mimas) and Ted Stryk (Miranda).>>
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JPL: Asteroid Photographer Beams Back Science Data

Postby bystander » Mon Aug 15, 2011 3:14 am

Asteroid Photographer Beams Back Science Data
NASA JPL-Caltech | Dawn | 2011 Aug 11
3D Image of Vesta's Equatorial Region
(Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

The Dawn spacecraft has completed a graceful spiral into the first of four planned science orbits during the spacecraft's yearlong visit to Vesta. The spacecraft started taking detailed observations on Aug. 11 at 9:13 a.m. PDT (12:13 a.m. EDT), which marks the official start of the first science-collecting orbit phase at Vesta, also known as the survey orbit.

Survey orbit is the initial and highest orbit, at roughly 1700 miles (2700 kilometers) above the surface, which will provide an overview or "big picture" perspective of the giant asteroid.

The primary objective of survey orbit is to image the surface with near-global coverage in visible and infrared wavelengths with the mapping spectrometer, also known as VIR. Dawn also will be using its framing camera to collect image mosaics that complement the VIR spectral data to produce geologic and compositional maps of Vesta's surface. Ultrasensitive measurements of the spacecraft's motion using radio signals will allow improved understanding of the giant asteroid's gravity field. Dawn's gamma ray and neutron detector will continue to collect background data.

The survey phase is planned to last 20 days. Each orbit takes almost three days, which will provide the spacecraft seven trips around Vesta. After survey orbit, Dawn will resume thrusting, taking about a month to spiral down gently to its next science orbit for an even closer view. That orbit, known as High Altitude Mapping Orbit, or HAMO, begins in late September. Dawn will spend about a month in HAMO, circling around Vesta in half a day, rather than three. Dawn will orbit more than 60 times during HAMO, allowing the camera to fully map the illuminated portion of Vesta at even higher resolution, and enable the science team to generate stereo images.
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Nature: Close-up of Vesta poses puzzle

Postby bystander » Mon Aug 15, 2011 3:40 am

Close-up of Vesta poses puzzle
Nature News | Ron Cowen | 2011 Aug 12
Astronomers keen to look into strange hole on second-largest asteroid.

Image
Vesta's large crater and equatorial ridges are mysterious.
(Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Planetary scientists thought they knew what to expect when NASA's Dawn spacecraft returned the first close-up portrait of the giant asteroid Vesta last month. Fuzzy images from the Hubble Space Telescope (HST) taken in 1996 seemed to show that something had taken a big bite out of the asteroid's south polar region1.

The crater was posited as the source of Vesta-like fragments that populate the asteroid belt, and of a surprisingly large fraction of the meteorites found on Earth.

But seconds after viewing the first image, Peter Thomas of Cornell University in Ithaca, New York, shot off an e-mail to other members of the team: "Looks like HST results were fantasy!"

Thomas later realized he had misjudged Dawn's location when he sent that e-mail, but his words give an idea of scientists' surprise. Vesta's huge depression isn't like those of most impact craters: it is ringed by a wall for only about half its circumference, says Dawn team member Paul Schenk of the Lunar and Planetary Institute in Houston, Texas. It also has a large rounded mound in its middle, rather than the usual conical uplift.

Perhaps strangest of all is a series of troughs ringing the asteroid's equator, a feature not seen in any other body in the Solar System and which may be related to the impact and its huge scale.

If it was caused by an impact, the crater is shaping up to be one of the biggest puzzles of the mission, says Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles.

Looking for answers

Russell has commissioned a task force of scientists on the Dawn team to solve the puzzle in time for two conferences in October.

New, sharper, images and spectra will help, as will maps of the asteroid's gravity. Dawn is now orbiting Vesta at a distance of about 2,700 kilometres, some six times closer than when the initial observations were made last month.

The task force will use the data gathered from this closer approach to hunt for evidence of whether the hole really was caused by some sort of collision. Tell-tale signs would include rock that has melted and resolidified on the floor of the depression, and a mixture of broken rock and melted material splashed out of the hole by the force of the blow.

Researchers have already come up with several possible explanations for the hole's strange shape. These all assume that the roughly 460-kilometre-wide crater was gouged out by a piece of space debris measuring 40-80 kilometres across.

One idea is that Vesta, which, at 530 kilometres across is the second-largest asteroid in the Solar System, was struck not at its south pole but midway between the pole and the equator. Because it spins rapidly, completing a full rotation in about five hours, Vesta would have reoriented itself so that the gouged-out region became the rock's new south pole.

This would be the most stable configuration for the damaged asteroid, says Schenk. "I don't think we've ever seen before a body with such a large impact and such a high rotation rate," he says.

In January, Martin Jutzi of the University of Bern in Switzerland and Erik Asphaug of the University of California, Santa Cruz, modelled the impact that walloped Vesta and obtained some surprising results2.

They calculate that Vesta completed an entire revolution while the crater was forming. As a result, the debris thrown up by the impact did not settle evenly around the crater, but fell in uneven clumps. This lopsided excavation might explain why a wall runs around only half of the impact site.

The cause of the equatorial troughs remain a mystery, says Asphaug, but they might be the result of material rushing back into the hole created by the impact. "We really don't know the physics when the crater gets to be about the size of the body [it strikes]," he says.

Russell is also hoping that Dawn will explain why Vesta is the brightest member of the asteroid belt, reflecting some 40% of the sunlight that hits it.

Images from the craft have already showed that some regions of the asteroid are brighter than average, and revealed dark streaks on the inside of craters. Compositional information recorded by Dawn's spectrometers may also show whether the bright regions are made from different material or whether they simply have a more crystalline structure, which scatters more light, Russell says.

  1. Impact Excavation on Asteroid 4 Vesta: Hubble Space Telescope Results - PC Thomas et al
  2. Mega-ejecta on asteroid Vesta - Martin Jutzi, Erik Asphaug
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Re: Dawn: Journey to the Asteroid Belt

Postby neufer » Wed Aug 17, 2011 12:25 am

NASA’s Dawn spacecraft obtained this image with its framing camera Aug. 6, 2011.
The framing camera has a resolution of about 260 meters per pixel.

Salvador Dalí obtained his The Persistence of Memory image in 1931.
[Note the dead olive :tree: tree.]
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Re: Dawn: Journey to the Asteroid Belt

Postby Ann » Wed Aug 17, 2011 2:11 am

Image


Well, clocks melt on Vesta, thanks to the energy released by the frequent meteor impacts.



But the ELEPHANTS stand tall, in honor of their

PATRON SAINT


Salvadorus Dalius

and the low gravity of
Vesta


Vesta, n. Note the lush urban landscape, blue skies and white clouds of V. Contrary to some reports, there are no dead olive :tree: trees on V.

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Dawn: Journey above Vesta

Postby bystander » Fri Sep 16, 2011 3:28 pm

Dawn Collects a Bounty of Beauty from Vesta
NASA JPL-Caltech | Dawn | 2011 Sept 16
Click to play embedded YouTube video.
NASA's Journey Above Vesta
New views of the second most massive object in the asteroid belt.

Click to play embedded YouTube video.
Vesta False Color Shape Model
This false-color video of the giant asteroid Vesta was created from
images taken by the framing camera aboard NASA's Dawn spacecraft.
A new video from NASA's Dawn spacecraft takes us on a flyover journey above the surface of the giant asteroid Vesta.

The data obtained by Dawn's framing camera, used to produce the visualizations, will help scientists determine the processes that formed Vesta's striking features. It will also help Dawn mission fans all over the world visualize this mysterious world, which is the second most massive object in the main asteroid belt.

The video shows Vesta as seen from Dawn's perspective.

You'll notice in the video that Vesta is not entirely lit up. There is no light in the high northern latitudes because, like Earth, Vesta has seasons. Currently it is northern winter on Vesta, and the northern polar region is in perpetual darkness. When we view Vesta's rotation from above the south pole, half is in darkness simply because half of Vesta is in daylight and half is in the darkness of night .

Another distinct feature seen in the video is a massive circular structure in the south pole region. Scientists were particularly eager to see this area close-up, since NASA's Hubble Space Telescope first detected it years ago. The circular structure, or depression, is several hundreds of miles, or kilometers, wide, with cliffs that are also several miles high. One impressive mountain in the center of the depression rises approximately 9 miles (15 kilometers) above the base of this depression, making it one of the highest elevations on all known bodies with solid surfaces in the solar system.

The collection of images, obtained when Dawn was about 1,700 miles (2,700 kilometers) above Vesta's surface, was used to determine its rotational axis and a system of latitude and longitude coordinates. One of the first tasks tackled by the Dawn science team was to determine the precise orientation of Vesta's rotation axis relative to the celestial sphere.

The zero-longitude, or prime meridian, of Vesta was defined by the science team using a tiny crater about 1,640 feet (500 meters) in diameter, which they named "Claudia," after a Roman woman during the second century B.C. Dawn's craters will be named after the vestal virgins-the priestesses of the goddess Vesta, and famous Roman women, while other features will be named for festivals and towns of that era.

[Nice slide show of Vesta images at the site]

Video: Zooming around Vesta
Planetary Society | Emily Lakdawalla | 2011 Sept 16

New Asteroid Close-Ups Show Giant Cliffs, Mountains and Craters
Wired Science | Dave Mosher | 2011 Sept 16

Take a Spin Around Asteroid Vesta!
Discovery News | Jason Major | 2011 Sept 16
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Dawn: Oblique View of Vesta's South Polar Region

Postby bystander » Tue Oct 11, 2011 2:17 am

Oblique View of Vesta's South Polar Region

This image of the asteroid Vesta, calculated from a shape model, shows a tilted view of the topography of the south polar region. The image has a resolution of about 1,000 feet (300 meters) per pixel, and the vertical scale is 1.5 times that of the horizontal scale.

This perspective shows the topography, but removes the overall curvature of Vesta, as if the giant asteroid were flat and not rounded. An observer on Vesta would not have a view like this, because the distant features would disappear over the curvature of the horizon. (In the same way, if you were standing in North America, you would not be able to see a tall Mt. Everest in the distance, because of Earth's curvature.)


Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI
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Dawn Discovers 2nd Giant South Pole Impact Basin at Vesta

Postby bystander » Tue Oct 18, 2011 3:06 am

Dawn Discovers Surprise 2nd Giant South Pole Impact Basin at Strikingly Dichotomous Vesta
Universe Today | Ken Kremer | 2011 Oct 17
Scientists leading’s NASA’s Dawn mission have discovered a 2nd giant impact basin at the south pole of the giant asteroid Vesta, which has been unveiled as a surprisingly “dichotomous” and alien world. Furthermore, the cosmic collisions that produced these two basins shuddered through the interior and created vast troughs, a Dawn scientist told Universe Today.

The newly discovered impact basin, nicknamed ‘Older Basin’, is actually significantly older in age compared to the initially discovered South Pole basin feature named ‘Rheasilvia’ – perhaps by more than a billion years. And that is just one of the many unexplained mysteries yet to be reconciled by the team as they begin to sift through the millions of bits of new data streaming back daily to Earth.

Scientists speculate that ‘Older Basin’ is on the order of 3.8 Billion years old, whereas ‘Rheasilvia’ might be as young as about 2.5 Billion years, but those are just tentative estimates at this time and subject to change. Measurements so far indicate Rheasilvia is composed of basaltic material.

“We found many surprising things at Vesta, which is quite unique and the results have exceeded our expectations”, said Dr. Carol Raymond, Dawn deputy principal investigator, of NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

Researchers presented the latest findings from Dawn’s initial science mapping orbit at a news briefing at the annual meeting of the Geological Society of America in Minneapolis, Minn., on Oct. 13.

The team considers Vesta to be the smallest terrestrial planet.

Since achieving orbit in July, Dawn’s Framing Cameras (FC) have imaged most of Vesta at about 250 meter resolution and the Visible and Infrared mapping spectrometer(VIR) at about 700 meter resolution. The measurements were collected at the survey orbit altitude of 2700 km. Before Dawn, Vesta was a fuzzy blob in humankind’s most powerful telescopes.

“There is a global dichotomy on Vesta and a fundamental difference between the northern and southern hemispheres”, said Raymond. “The northern hemisphere is older and heavily cratered in contrast to the brighter southern hemisphere where the texture is more smooth and there are lots of sets of grooves. There is a massive mountain at the South Pole. One of the more surprising aspects is the set of deep equatorial troughs.”

“There is also a tremendous and surprising diversity of surface color and morphology. The south is consistent with basaltic lithology and the north with impacts. We are trying to make sense of the data and will integrate that with the high resolution observations we are now collecting.”

Indeed Vesta’s completely unique and striking dichotomy can be directly traced back to the basins which were formed by ancient cataclysmic impacts resulting in shockwaves that fundamentally altered the surface and caused the formation of the long troughs that ring Vesta at numerous latitudes.

“The troughs extend across 240 degrees of longitude,” said Debra Buczkowski, Dawn participating scientist, of the Applied Physics Laboratory at Johns Hopkins University, Laurel, Md. “Their formation can be tied back to the two basins at the South Pole.”

In an exclusive follow up interview with Universe Today, Raymond said “We believe that the troughs formed as a direct result of the impacts,” said “The two sets of troughs are associated with the two large basins [Rheasilvia and Older Basin].”

“The key piece of evidence presented was that the set of troughs in the northern hemisphere, that look older (more degraded) are circumferential to the older impact basin,” Raymond told me.

“The equatorial set are circumferential to Rheasilvia. That Rheasilvia’s age appears in places to be much younger is at odds with the age of the equatorial troughs. An explanation for that could be resurfacing by younger mass wasting features (landslides, slumps). We will be working on clarifying all these relationships in the coming months with the higher resolution HAMO (High Altitude Mapping Orbit) data.”

Dawn has gradually spiraled down closer to Vesta using her exotic ion thrusters and began the HAMO mapping campaign on Sept. 29.

Surface features are dated by crater counting methodology.

“Preliminary crater counting age dates for the equatorial trough region yields a very old age (3.8 Billion years). So there is a discrepancy between the apparent younger age for the Rheasilvia basin and the old age for the troughs. These could be reconciled if Rheasilvia is also 3.8 Billion years old but the surface has been modified by slumping or other processes,” Raymond elaborated.

Time will tell as further data is analyzed.

“Vesta is full of surprises, no more so than at the South Pole,” said Paul Schenk at the GSA briefing. Schenk is a Dawn participating scientist of the Lunar and Planetary Institute, Houston, Texas.

The ‘Rheasilvia’ basin was initially discovered in images of Vesta taken a decade ago by the Hubble Space Telescope which revealed it as a gaping hole in the southern hemisphere. But it wasn’t until Dawn entered orbit on July 16, 2011 after a nearly four year interplanetary journey that Earthlings got their first close up look at the mysterious polar feature and can now scrutinize it in detail to elucidate its true nature.

“The South Pole [Rheasilvia] basin is a roughly circular, impact structure and a deep depression dominated by a large central mound,” said Schenk. “It shows sharp scarps, smooth areas, landslide deposits, debris flows. It’s about 475 km in diameter and one of the deepest (ca. 20 -25 km) impact craters in the solar system.”

The central peak is an enormous mountain, about 22 km high and 180 km across- one of the biggest in the solar system. “It’s comparable in some ways to Olympus Mons on Mars,” Schenk stated.

“We were quite surprised to see a second basin in the mapping data outside of Rheasilvia. This was unexpected. It’s called ‘Older Basin’ for now.”

‘Older Basin’ is about 375 km in diameter. They overlap at the place where Rheasilvia has a missing rim.

“These basins are interesting because we believe Vesta is the source of a large number of meteorites, the HED meteorites that have a spread of ages,” Schenk explained.

Multiple large impacts over time may explain the source of the HED (Howardite, Eucrite and Diogenite) meteorites.

“We did expect large impacts on Vesta, likely associated with the late heavy bombardment recognized in the lunar impact record,” Raymond told Universe Today. “The surprising element is that the two apparently largest impacts – keeping in mind that other larger impact basins may be lurking under the regolith – are overlapping.”

Dawn’s VIR spectrometer has detected pyroxene bands covering Vesta’s surface, which is indicative of typical basaltic material, said Federico Tosi, a VIR team member of the Italian Space Agency, Rome. “Vesta has diverse rock types on its surface.”

“VIR measured surface temperatures from 220K to 270 K at the 5 micron wavelength. The illuminated areas are warmer.”

So far there is no clear indication of olivine which would be a marker for seeing Vesta’s mantle, Tossi elaborated.

The VIR spectrometer combines images, spectral information and temperature that will allow researchers to evaluate the nature, composition and evolutionary forces that shaped Vesta’s surface.

The team is absolutely thrilled to see a complicated geologic record that’s been preserved for study with lots of apparent surface layering and surprisingly strong and complex structural features with a large range of color and brightness.

Stay tuned !
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JPL: Dawn Obtains First Low Altitude Images of Vesta

Postby bystander » Sat Dec 24, 2011 6:47 pm

Is Vesta the "Smallest Terrestrial Planet?"
NASA Science News | Dauna Coulter | 2011 Dec 09

Dawn Spirals Down to Lowest Orbit
NASA JPL-Caltech | 2011 Dec 13

Dawn Obtains First Low Altitude Images of Vesta
NASA JPL-Caltech | 2011 Dec 21

Dawn Image Gallery
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PS: Dawn images of Vesta! Released!! For everyone!!!

Postby bystander » Wed Feb 15, 2012 2:15 pm

Dawn images of Vesta! Released!! For everyone!!!
Planetary Society | Emily Lakdawalla | 2012 Feb 14
Can you tell I'm a little bit excited about this? Some time in the last few days, the Dawn team made public the first preliminary version of the first release of their data from the Vesta phase of their mission. This is soooo much sooner than I had understood that this data release would happen. It's only been nine months since the ion-powered Dawn spacecraft began its exploration of a never-before-visited world. Vesta is the second largest asteroid, about 550 kilometers across. It's similar in size to Saturn's moons Mimas and Enceladus, but an utterly different place. Before Dawn, it was not much more than a smudgy spot of light. Now, it's a new world, still being explored by Dawn as it orbits only 200-ish kilometers above the surface.
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Re: Dawn: Journey to the Asteroid Belt

Postby bystander » Thu Apr 19, 2012 1:59 am

Dawn Gets Extra Time to Explore Vesta
NASA JPL-Caltech | Dawn | 2012 Apr 18
Dawn Orbiting Vesta - Credit: NASA/JPL-Caltech
NASA's Dawn mission has received official confirmation that 40 extra days have been added to its exploration of the giant asteroid Vesta, the second most massive object in the main asteroid belt. The mission extension allows Dawn to continue its scientific observations at Vesta until Aug. 26, while still arriving at the dwarf planet Ceres at the same originally scheduled target date in February 2015.

"We are leveraging our smooth and successful operations at Vesta to provide for even more scientific discoveries for NASA and the world." said Robert Mase, Dawn project manager based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This extra time will allow us to extend our scientific investigation and learn more about this mysterious world."

The extension will not require any new funding, and will draw on financial reserves that have been carefully managed by the Dawn project. The flexibility provided by the spacecraft's use of efficient ion propulsion system allows it to maintain its originally planned Ceres arrival.

The extension allows for extra observations at Dawn's current low-altitude mapping orbit (average altitude 130 miles or 210 kilometers), which will now last until May 1. The additional time enables the gamma ray and neutron detector to build the best possible maps of the elemental composition of Vesta's surface and improve data for the gravity experiment, the two primary scientific investigations at the low-altitude orbit. The spacecraft's camera and spectrometer are also obtaining additional high-resolution images.

Additional time will also be spent in the planned second high-altitude mapping orbit later this summer. When Dawn arrived at Vesta in July 2011, much of the northern hemisphere was in shadow. But with the passage of time, more of that area will bask in sunshine.

"Dawn has beamed back to us such dazzling Vestan vistas that we are happy to stay a little longer and learn more about this special world," said Christopher Russell, Dawn's principal investigator at UCLA. "While we have this one-of-a-kind opportunity to orbit Vesta, we want to make the best and most complete datasets that we can."
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Re: Dawn: Journey to the Asteroid Belt

Postby owlice » Thu Apr 19, 2012 11:57 am

Yay!! Very cool!!
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Dawn Mission Reveals Secrets of Large Asteroid

Postby bystander » Mon May 14, 2012 2:44 am

Dawn Mission Reveals Secrets of Large Asteroid
NASA | JPL-Caltech | Dawn Mission Page | 2012 May 10
Mineral Diversity at Vesta's South Pole
(Image credit: NASA/JPL-Caltech/UCLA/INAF/MPS/DLR/IDA)

Vesta in Perspective (Image credit: NASA/JPL-Caltech/UCLA)


Click to play embedded YouTube video.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI
NASA's Dawn spacecraft has provided researchers with the first orbital analysis of the giant asteroid Vesta, yielding new insights into its creation and kinship with terrestrial planets and Earth's moon.

Vesta now has been revealed as a special fossil of the early solar system with a more varied, diverse surface than originally thought. Scientists have confirmed a variety of ways in which Vesta more closely resembles a small planet or Earth's moon than another asteroid. Results appear in today's edition of the journal Science.

"Dawn's visit to Vesta has confirmed our broad theories of this giant asteroid's history, while helping to fill in details it would have been impossible to know from afar," said Carol Raymond, deputy principal investigator at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Dawn's residence at Vesta of nearly a year has made the asteroid's planet-like qualities obvious and shown us our connection to that bright orb in our night sky."

Scientists now see Vesta as a layered, planetary building block with an iron core - the only one known to survive the earliest days of the solar system. The asteroid's geologic complexity can be attributed to a process that separated the asteroid into a crust, mantle and iron core with a radius of approximately 68 miles (110 kilometers) about 4.56 billion years ago. The terrestrial planets and Earth's moon formed in a similar way.

Dawn observed a pattern of minerals exposed by deep gashes created by space rock impacts, which may support the idea the asteroid once had a subsurface magma ocean. A magma ocean occurs when a body undergoes almost complete melting, leading to layered building blocks that can form planets. Other bodies with magma oceans ended up becoming parts of Earth and other planets.

Data also confirm a distinct group of meteorites found on Earth did, as theorized, originate from Vesta. The signatures of pyroxene, an iron- and magnesium-rich mineral, in those meteorites match those of rocks on Vesta's surface. These objects account for about 6 percent of all meteorites seen falling on Earth.

This makes the asteroid one of the largest single sources for Earth's meteorites. The finding also marks the first time a spacecraft has been able to visit the source of samples after they were identified on Earth.

Scientists now know Vesta's topography is quite steep and varied. Some craters on Vesta formed on very steep slopes and have nearly vertical sides, with landslides occurring more frequently than expected.

Another unexpected finding was that the asteroid's central peak in the Rheasilvia basin in the southern hemisphere is much higher and wider, relative to its crater size, than the central peaks of craters on bodies like our moon. Vesta also bears similarities to other low-gravity worlds like Saturn's small icy moons, and its surface has light and dark markings that don't match the predictable patterns on Earth's moon.

"We know a lot about the moon and we're only coming up to speed now on Vesta," said Vishnu Reddy, a framing camera team member at the Max Planck Institute for Solar System Research in Germany and the University of North Dakota in Grand Forks. "Comparing the two gives us two storylines for how these fraternal twins evolved in the early solar system."

Dawn has revealed details of ongoing collisions that battered Vesta throughout its history. Dawn scientists now can date the two giant impacts that pounded Vesta's southern hemisphere and created the basin Veneneia approximately 2 billion years ago and the Rheasilvia basin about 1 billion years ago. Rheasilvia is the largest impact basin on Vesta.

"The large impact basins on the moon are all quite old," said David O'Brien, a Dawn participating scientist from the Planetary Science Institute in Tucson, Ariz. "The fact that the largest impact on Vesta is so young was surprising."

Dawn Vesta Image Gallery

Dawn spacecraft reveals complexities of ancient asteroidal world
Arizona State University | 2012 May 10

Asteroid collision that spawned Vesta's asteroid family occurred more recently than originally thought
Southwest Research Institute | 2012 May 10

Dawn Reveals Asteroid Vesta’s Role in Solar System History
Planetary Science Institute | 2012 May 10

Vesta seen in colors
Max Planck Gesellschaft | 2012 May 10

Dawn mission shows protoplanet's surprising surface
University of California, Los Angeles | 2012 May 10

ScienceShot: Asteroid Vesta As a Failed Planet
Science NOW | Richard A. Kerr | 2012 May 10

Vesta is a Baby Planet, Not an Asteroid
Discovery News | Irene Klotz | 2012 May 10

Dawn flies over Vesta
Discover Blogs | Bad Astronomy | 2012 May 10

Fly Over Vesta’s Cratered Terrain with Dawn
Universe Today | Nancy Atkinson | 2012 May 10

Dawn at Vesta: Testing the Protoplanetary Paradigm - C. T. Russell et al
Vesta’s Shape and Morphology - R. Jaumann et al
The Violent Collisional History of Asteroid 4 Vesta - S. Marchi et al
The Geologically Recent Giant Impact Basins at Vesta’s South Pole - Paul Schenk et al
Spectroscopic Characterization of Mineralogy and Its Diversity Across Vesta - M. C. De Sanctis et al
Color and Albedo Heterogeneity of Vesta from Dawn - Vishnu Reddy et al
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Astrophile: Two craters that launched 1000 meteorites

Postby bystander » Mon May 14, 2012 3:02 am

Two craters that launched 1000 meteorites
New Scientist | Astrophile | Lisa Grossman | 2012 May 11
Shape and Gravity of Vesta's South Pole - A false-colour topographical map of Vesta's South Pole. Rheasilvia Basin is the top left circle; Veneneia Basin is the fainter circle on the bottom right. (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Object: Impact craters on the asteroid Vesta
Size: Up to 500 kilometres wide

Vesta thought its days of being the solar system's punching bag were over. Despite 3.5 billion years of pummelling, the protoplanet had managed to hold itself together. The bullies of the asteroid playground had mostly settled down, and aside from the occasional shove or taunt, things were starting to look up. If only poor Vesta had known of the two bullies that were still to come.

Fresh images of 4.5 billion year old Vesta show the poor protoplanet was pummelled by a 60-kilometre-wide rock not once, but twice, in the past two billion years. And those strikes dug up enough material to create an entire class of meteorites. If Helen of Troy had "the face that launched a thousand ships", then Vesta has Rheasilvia and Veneneia, the craters that launched a thousand meteorites.

Astronomers had suspected for decades that Vesta – the solar system's second-biggest asteroid – was the source of the howardite-eucrite-diogenite, or HED meteorites. This common group of space rocks makes up about 6 per cent of the meteorites seen to fall to Earth: the Meteoritical Bulletin Database lists 1082 that have been found on the ground.

Both the asteroid and HED meteorites give off similar spectral signatures that were different from other classes of meteorites, and both looked like basaltic lava of the sort that is found in Hawaii. Vesta's orbit around the sun is also just right for sending debris to Earth. Meanwhile, observations with the Hubble Space Telescope in 1997 showed a giant crater in the South Pole. That was the "smoking gun", says Paul Schenk of the Lunar and Planetary Institute in Houston, Texas. But a few mysteries remained.

Groovy impact

Could a single hole in Vesta's South Pole really have dug up enough material to account for all HED meteorites? How deep is the hole, and how long ago did it form? And how many impacts were there? A group of smaller asteroids called Vestoids are thought to be chips of Vesta knocked off in a giant impact. But some studies of the way they move had suggested that these are divided into two distinct populations – one about a billion years older than the other.

New images from NASA's Dawn spacecraft are filling in the details. Dawn slipped into orbit on 17 July, 2011 and has mapped nearly 80 per cent of the asteroid's surface. The images show that Vesta's northern hemisphere is pockmarked with craters, a record of billions of years of pummelling. "It's been hammered quite a bit," Schenk says.

But whatever craters had been preserved in the southern hemisphere were obliterated by one huge impact, which Schenk and colleagues estimate came about a billion years ago. The crater this vast asteroid bully left behind, called Rheasilvia, stretches to 500 kilometres, wider than the distance from London to Dublin and spanning most of Vesta itself. It's at least 19 kilometres deep, and has a central peak that rises 20 kilometres high, higher than Mauna Kea on Hawaii.

That means the object that hit Vesta must have been 50 to 60 kilometres wide, bigger than the object that made the Chicxulub impact crater thought to be responsible for killing off the dinosaurs. Debris from the crater can be found 100 kilometres away from the rim. The force of the impact formed deep grooves that circle Vesta's equator.

Meet Veneneia

"It's the largest possible ring you can make due to an impact," says Chris Russell of the University of California, Los Angeles. "We've never seen anything like that before."

The team calculated that the impact scooped a million cubic kilometres worth of material out of Vesta's South Pole, and scattered much of it into space. The HED meteorites plus the Vestoids have a total estimated volume of 100,000 cubic kilometres, so the Rheasilvia impact alone could have been responsible for the lot.

But beneath all the destruction the researchers also found a second impact crater, Veneneia, almost as large as Rheasilvia but half-hidden underneath it. About 400 kilometres wide and 12 kilometres deep, it formed about two billion years ago, Schenk and colleagues determined.
Iron core

"That was a surprise, that in fact the southern part of Vesta had been subject to two very large impacts," Russell says. Vesta probably would have been destroyed by the one-two punch, if not for a characteristic that makes it seem more planet than asteroid: an iron core. In its first million years of existence, Vesta was completely molten, Russell says, and the heavier elements like iron sank to its centre to congeal into a solid metallic core.

"It was anchored by that iron core, and survived," he says. "And fortunately so, because we don't have many ways of getting back that far in history, to get some evidence of what was going on in those very early days."

There's another silver lining to Vesta's tortured playground years: HED meteorites are so numerous, you could own one. "You can go to a meteorite collection store, and they'll sell you a piece of Vesta," says Russell.

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JPL: Dawn Shows Vesta's Coat of Many Colors

Postby bystander » Wed Jun 06, 2012 8:26 pm

Dawn Mission Video Shows Vesta's Coat of Many Colors
NASA JPL-Caltech | Dawn | 2012 June 06
Click to play embedded YouTube video.
A new video from NASA's Dawn mission reveals the dappled, variegated surface of the giant asteroid Vesta. The animation drapes high-resolution false color images over a 3-D model of the Vesta terrain constructed from Dawn's observations. This visualization enables a detailed view of the variation in the material properties of Vesta in the context of its topography.

The colors were chosen to highlight differences in surface composition that are too subtle for the human eye to see. Scientists are still analyzing what some of the colors mean for the composition of the surface. But it is clear that the orange material thrown out from some impact craters is different from the surrounding surface material. Green shows the relative abundance of iron. Parts of the huge impact basin known as Rheasilvia in Vesta's southern hemisphere, for instance, have areas with less iron than nearby areas.

Dawn has imaged the majority of the surface of Vesta with the framing camera to provide this 3-D map. While some areas in the north were in shadow at the time the images were obtained by the camera, Dawn expects to improve its coverage of Vesta's northern hemisphere with additional observations. Dawn's viewing geometry also prevented mapping of a portion of the mountain of the south pole.

The spacecraft is currently spiraling up from its lowest-altitude orbit into its final science orbit, where its average altitude will be about 420 miles (680 kilometers). Dawn is scheduled to leave Vesta around Aug. 26.

Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Vesta’s Amazing Technicolor Surface
Universe Today | Nancy Atkinson | 2012 June 06
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Re: Dawn: Journey to the Asteroid Belt

Postby neufer » Thu Jun 07, 2012 10:26 am

laptops4college wrote:
If this asteroid will go nearer to our planet, this could be dangerous to as humans..

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JPL: Dawn Engineers Assess Reaction Wheel

Postby bystander » Wed Aug 15, 2012 12:12 am

Dawn Engineers Assess Reaction Wheel
NASA | JPL-Caltech | Dawn | 2012 Aug 13
Dawn Orbiting Vesta - Credit: NASA/JPL-Caltech
Engineers working on NASA's Dawn spacecraft are assessing the status of a reaction wheel -- part of a system that helps the spacecraft point precisely -- after onboard software powered it off on Aug. 8. Dawn's mission is to study the geology and geochemistry of the giant asteroid Vesta and dwarf planet Ceres, the two most massive objects in the main asteroid belt. Dawn is now using its thrusters to point at Earth for communications. The rest of the spacecraft is otherwise healthy.

During a planned communications pass on Aug. 9, the team learned that the reaction wheel had been powered off. Telemetry data from the spacecraft suggest the wheel developed excessive friction, similar to the experience with another Dawn reaction wheel in June 2010. The Dawn team demonstrated during the cruise to Vesta in 2011 that, if necessary, they could complete the cruise to Ceres without the use of reaction wheels.

The spacecraft has been orbiting Vesta since July 15, 2011. Dawn concluded its primary science observations of Vesta on July 25, 2012, and has been spiraling slowly away from the giant asteroid using its ion propulsion system. Ion thrusting was halted to accommodate the reaction wheel investigation, which may briefly delay the escape from Vesta.

"The Vesta mission has been spectacularly successful, and we are looking forward to the exciting Ceres mission ahead of us," said Robert Mase, Dawn project manager, of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
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JPL: Dawn Prepares for Trek Toward Dwarf Planet

Postby bystander » Thu Aug 30, 2012 6:48 pm

Dawn Prepares for Trek Toward Dwarf Planet
NASA JPL-Caltech | Dawn | 2012 Aug 30
Click to play embedded YouTube video.
NASA's Dawn spacecraft is on track to become the first probe to orbit and study two distant solar system destinations, to help scientists answer questions about the formation of our solar system. The spacecraft is scheduled to leave the giant asteroid Vesta on Sept. 4 PDT (Sept. 5 EDT) to start its two-and-a-half-year journey to the dwarf planet Ceres.

Dawn began its 3-billion-mile (5-billion kilometer) odyssey to explore the two most massive objects in the main asteroid belt in 2007. Dawn arrived at Vesta in July 2011 and will reach Ceres in early 2015. Dawn's targets represent two icons of the asteroid belt that have been witness to much of our solar system's history.

To make its escape from Vesta, the spacecraft will spiral away as gently as it arrived, using a special, hyper-efficient system called ion propulsion. Dawn's ion propulsion system uses electricity to ionize xenon to generate thrust. The 12-inch-wide ion thrusters provide less power than conventional engines, but can maintain thrust for months at a time.

"Thrust is engaged, and we are now climbing away from Vesta atop a blue-green pillar of xenon ions," said Marc Rayman, Dawn's chief engineer and mission director, at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We are feeling somewhat wistful about concluding a fantastically productive and exciting exploration of Vesta, but now have our sights set on dwarf planet Ceres.

Dawn's orbit provided close-up views of Vesta, revealing unprecedented detail about the giant asteroid. The mission revealed that Vesta completely melted in the past, forming a layered body with an iron core. The spacecraft also revealed the scarring from titanic collisions Vesta suffered in its southern hemisphere, surviving not one but two colossal impacts in the last two billion years. Without Dawn, scientists would not have known about the dramatic troughs sculpted around Vesta, which are ripples from the two south polar impacts.

"We went to Vesta to fill in the blanks of our knowledge about the early history of our solar system," said Christopher Russell, Dawn's principal investigator, based at the University of California Los Angeles (UCLA). "Dawn has filled in those pages, and more, revealing to us how special Vesta is as a survivor from the earliest days of the solar system. We can now say with certainty that Vesta resembles a small planet more closely than a typical asteroid."
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