MESSENGER: Earth and Moon from 114 Million Miles

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MESSENGER: Earth and Moon from 114 Million Miles

Post by bystander » Tue Aug 17, 2010 6:10 pm

Earth and Moon from 114 Million Miles
MESSENGER Featured Release | 17 Aug 2010
In the lower left portion of this image, the Earth can be seen, as well as the much smaller Moon to Earth's right. When MESSENGER took this image, a distance of 183 million kilometers (114 million miles) separated the spacecraft and Earth. To provide context for this distance, the average separation between the Earth and the Sun is about 150 million kilometers (93 million miles).

Though it is a beautiful, thought-provoking picture, viewing our planet from far away was not the main reason that the mission team planned the collection of this image. Instead, this image was acquired as part of MESSENGER's campaign to search for vulcanoids, small rocky objects that have been postulated to exist in orbits between Mercury and the Sun. Though no vulcanoids have yet been detected, the MESSENGER spacecraft is in a unique position to look for smaller and fainter vulcanoids than has ever before been possible. MESSENGER's vulcanoid searches occur near perihelion passages, when the spacecraft's orbit brings it closest to the Sun. Today is another such perihelion, and MESSENGER is taking a new set of images to search for tiny asteroids lurking close to the Sun.


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Re: MESSENGER: Earth and Moon from 114 Million Miles

Post by mexhunter » Tue Aug 17, 2010 6:22 pm

Very true, invites to reflection.
As this picture was oldest:
Many grettings
I come to learn and to have fun.

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A distant Spock

Post by neufer » Thu Aug 19, 2010 2:43 pm wrote:
Mercury Probe Searches for Vulcanoids, Spies Venus
Posted on February 2, 2010

<<The closer stuff is to the sun, the harder it is to see. That's the fundamental problem with vulcanoids, a hypothetical band of asteroids orbiting between the sun and the closest planet in, Mercury. In fact, for years that was the problem with studying Mercury, since looking at the tiny planet through a backyard telescope is like trying to make out the patterns on a moth's wing as it sits on a football stadium floodlight. Bigger telescopes on the ground or in Earth orbit can see the planet, but in doing so, glare from the sun would damage the instruments' sensitive lenses. Even Hubble, capable of peering into the far reaches of the universe, can't safely look too hard at the innermost planet. To really see details on Mercury, you need a spacecraft that gets close enough to keep the sun's glare out of the frame. Mariner 10 gave humans our first good look at Mercury during a series of flybys in 1974 and 1975. But that mission was able to take pictures of just half the planet—we had to wait until January 2008 to see the other side!
Our first glimpse of Mercury's "hidden" face came via the MESSENGER mission, a spacecraft now swirling around Mercury in a gravitational dance that will eventually see the probe settle into orbit in 2011. Along the way, MESSENGER has been taking scads of pictures, and one of its targets has been the stretch of space inside Mercury's orbit where small, faint vulcanoids could be hiding. MESSENGER has been making its vulcanoid searches when its orbit brings it closest to the sun. The craft has taken a host of snapshots in June 2008, February 2009, and most recently in January 2010. So far, nada. But on January 16 MESSENGER did get an eyeful of neighboring Venus, the brightest dot in this polka dotted field of view. Of course, Venus is so wildly overexposed in this picture that it looks like someone shot a hole in the sky. But that highlights just how hard MESSENGER has to stare to even hope to catch a glimpse of a vulcanoid—if any are out there at all.

The concept of vulcanoids arose from research done in the late 1800s, when astronomers trying to use the classical rules of celestial mechanics to chart Mercury's orbit kept finding things wrong with their calculations. French mathematician Urbain Jean Joseph le Verrier took the challenge to heart, and in 1860 he announced that discrepancies in Mercury's orbit were due to an unseen planet, which he named Vulcan. Le Verrier's theory was eventually disproven thanks to Einstein's revolutionary theory of relativity—when you include the sun's gravitational field in the mix, Mercury's orbit works out just fine, thanks, no extra planet required. But the concept of something being between Mercury and the sun has lived long and prospered, and a number of missions (some using fighter jets!) have kept the search alive over the years.>> wrote: <<The Vulcan homeworld, also named Vulcan, was never identified in the original series, but in the novel Star Trek 2, author James Blish put the planet in orbit around the star 40 Eridani A, 16 light years from Earth, an identification later adopted by Roddenberry. Vulcan is a reddish Minshara-Class planet. Its inhabitants were originally called Vulcanians.

Much of its surface consists of deserts and mountain ranges, and large areas are set aside as wilderness preserves. It is much hotter, it has a stronger surface gravity, and its atmosphere is thinner than that of Earth. As a result of these factors, humans tend to tire out more quickly than native Vulcans. In the alternate timeline of the 2009 film the planet was destroyed by Nero who created a black hole in the center of Vulcan. The planet imploded, leaving an estimated 10,000 survivors out of a population of 6 billion, including Spock and some of the Elders.>> wrote:
<<Celestial bodies interior to the orbit of Mercury have been hypothesized, and searched for, for centuries. The German astronomer Christoph Scheiner believed he had seen small bodies passing in front of the Sun in 1611, but these were later shown to be sunspots. In the 1850s, Urbain Le Verrier made detailed calculations of Mercury's orbit and found a small discrepancy in the planet's perihelion precession from predicted values. He postulated that the gravitational influence of a small planet or ring of asteroids within the orbit of Mercury would explain the deviation. Shortly afterward, an amateur astronomer named Edmond Lescarbault claimed to have seen Le Verrier's proposed planet transit the Sun. The new planet was quickly named Vulcan but was never seen again, and the anomalous behaviour of Mercury's orbit was explained by Einstein's General theory of relativity in 1915. The vulcanoids take their name from this hypothetical planet. What Lescarbault saw was probably another sunspot.
There is evidence that Mercury was struck by a large object relatively late in its development, a collision which stripped away much of Mercury's crust and mantle, and explaining the thinness of Mercury's mantle compared to the mantles of the other terrestrial planets. If such an impact occurred, much of the resulting debris might still be orbiting the Sun in the vulcanoid zone. The outer edge of the vulcanoid zone is approximately 0.21 AU from the Sun. More distant objects are unstable due to the gravitational influence of Mercury and would be perturbed into Mercury-crossing orbits on timescales of the order of 100 million years. The inner edge is not sharply defined: objects closer than 0.06 AU are highly susceptible to Poynting-Robertson drag and the Yarkovsky effect, and even out to 0.09 AU vulcanoids would have temperatures of 1,000 K or more, which is hot enough for evaporation of rocks to be the limiting factor in their lifetime. There may be no more than 300–900 vulcanoids larger than 1 kilometre (0.62 mi) in radius remaining, if any. The gravitational stability of the vulcanoid zone is due in part to the fact that there is only one neighbouring planet. In that respect it can be compared to the Kuiper belt.

The volume of the vulcanoid zone is very small compared to the main belt of asteroids. Collisions between objects in the vulcanoid zone would be frequent and highly energetic, tending to lead to the destruction of the objects. The most favourable location for vulcanoids is probably in circular orbits near the outer edge of the vulcanoid zone. Vulcanoids are unlikely to have inclinations of more than about 10° to the ecliptic. Mercury trojans, asteroids trapped in Mercury's Lagrange points, are also possible.

Any vulcanoids that exist must be relatively small. Previous searches, particularly from the SOHO spacecraft, rule out asteroids larger than 60 kilometres in diameter. The minimum size is about 100 metres since objects smaller than 70 m would be drawn into the Sun by Poynting-Robertson drag. Between these upper and lower limits, a population of asteroids between 1 kilometre and 25 kilometres in diameter is thought to be possible. They would be almost hot enough to glow red hot. Although every other gravitationally stable region in the Solar System has been found to contain objects, non-gravitational forces, such as the Yarkovsky effect, or the influence of a migrating planet in the early stages of the Solar System's development may have depleted this area of any asteroids that may have been there.

If they do exist, the vulcanoids could easily evade detection because they would be very small and drowned out by the bright glare of the nearby Sun. Due to their proximity to the Sun, searches from the ground can only be carried out during twilight or solar eclipses. They are most likely to be between 100 metres and 60 kilometres in diameter and located in nearly circular orbits near the outer edge of the gravitationally stable zone.

In 1998, astronomers analysed data from the SOHO spacecraft's LASCO instrument, which is a set of three coronagraphs. The data taken between January and May of that year did not show any vulcanoids brighter than magnitude 7. This corresponds to a diameter of about 60 kilometres (37 mi), assuming the asteroids have an albedo similar to that of Mercury. In particular a large planetoid at a distance of 0.18AU, predicted by the theory of Scale relativity, was ruled out.

In 2000, planetary scientist Alan Stern performed surveys of the vulcanoid zone using a Lockheed U-2 spy plane. The flights were conducted at a height of 21,300 metres during twilight. In 2002, he and Dan Durda performed similar observations on an F-18 fighter jet. They made three flights over the Mojave desert at an altitude of 15,000 metres and made observations with the Southwest Universal Imaging System—Airborne (SWUIS-A).

The MESSENGER space probe may provide evidence regarding vulcanoids. Its opportunities will be limited because its instruments need to be pointed away from the Sun at all times to avoid damage. The spacecraft has already taken a few of a planned series of images of the outer regions of the vulcanoid zone. [The most favourable location for vulcanoids is probably in circular orbits near the outer edge of the vulcanoid zone.]

It is believed that the vulcanoids would be very rich in elements with a high melting point, such as iron and nickel. They are unlikely to possess a regolith because such fragmented material heats and cools more rapidly, and is affected more strongly by the Yarkovsky effect, than solid rock. Vulcanoids are probably similar to Mercury in colour and albedo, and may contain material left over from the earliest stages of the Solar System's formation.

Vulcanoids, being an entirely new class of celestial bodies, would be interesting in their own right, but discovering whether or not they exist would yield insights into the formation and evolution of the Solar System. If they exist they might contain material left over from the earliest period of planet formation, and help determine the conditions under which the terrestrial planets, particularly Mercury, formed. In particular, if vulcanoids exist or did exist in the past, they would represent an additional population of impactors that have affected no other planet but Mercury making that planet's surface appear older than it actually is. If vulcanoids are found not to exist, this would place different constraints on planet formation and suggest that other processes have been at work in the inner solar system, such as planetary migration clearing out the area.>> ... 43#p106343 wrote:
<<Vulcanoids are small, rocky bodies that circle the Sun in stable orbits inside the orbit of Mercury. Being small, faint objects, orbiting in the immediate vicinity of the Sun, Vulcanoids are easily lost in the blinding solar glare and cannot be viewed with ordinary Earth-based telescopes. They have proven to be some of the most elusive objects in the solar system, foiling every attempt to observe them.

In 2003, Researchers Alan Stern and Dan Durda, of the Space Science Department at the Southwest Research Institute (SwRI) in Boulder, Colorado, asked for support from The Planetary Society to fly a sensitive camera called VULCAM aboard a rocket on a brief, 10-minute suborbital flight. With the generous support of members of The Planetary Society, and a matching grant from Society supporter Mark Gelfand, Stern and Durda launched their rocket on January 16, 2004. The flight carried the camera above Earth's atmosphere and acquired more than 50,000 images of the region that should have contained Vulcanoids. Unfortunately, a technical problem prevented these images from revealing any Vulcanoids.

"Any Vulcanoids that may wander the inner frontier of the solar system elude us still," Durda wrote in an article for The Planetary Report. "It's clear that future Vulcanoid searches using the Earth's limb to block the Sun will have to pay close attention to beating the problem of scattered light from the twilight limb. We won't be throwing in the towel on the search for Vulcanoids anytime soon. This is a challenging observational problem we want to solve, and knowing once and for all whether any Vulcanoids exist today—and what their properties are—is important to planetary science.">>
Art Neuendorffer

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Re: A distant Spock

Post by neufer » Sat Aug 11, 2018 6:26 pm wrote:
The Wide-Field Imager for Solar Probe Plus (WISPR)
Space Sci Rev DOI 10.1007/s11214-014-0114-y
Received: 20 March 2014 / Accepted: 20 October 2014
© Springer Science+Business Media Dordrecht (outside the USA) 2014

<<Another unique [Parker Solar Probe] science opportunity is the search for planetoids within the Mercury orbit. A dynamically stable region interior to Mercury’s orbit is predicted to contain a population of small, asteroid like bodies called Vulcanoids from the early solar system and may be the source of impacts onto Mercury. Searches for the existence of Vulcanoids have not been successful. Messenger and SECCHI observations to search for Vulcanoid objects and have put upper limits on the number of objects above certain sizes. While asteroids have been detected within the Vulcanoid region (0.08–0.2 AU), none were Vulcanoids. With WISPR, we will be able to extend these searches to fainter objects and place new constraints on the formation and evolution of objects in this region.>>
Art Neuendorffer