* Astronomy

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RE: Vesta

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Giant Asteroid's Troughs Suggest Stunted Planet

Enormous troughs that wrap around the giant asteroid Vesta may actually be dropped blocks of terrain bounded by fault lines, suggesting a geologic complexity beyond that of most asteroids. Since the discovery of the troughs last year in data from NASA's Dawn spacecraft, scientists have been working to determine the story behind these unusual features. The research reinforces the claim that Vesta has a core, mantle and crust, a structure normally reserved for larger bodies, such as planets and large moons.
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Dawn Sees Hydrated Minerals on Giant Asteroid

NASA's Dawn spacecraft has revealed that the giant asteroid Vesta has its own version of ring around the collar. Two new papers based on observations from the low-altitude mapping orbit of the Dawn mission show that volatile, or easily evaporated materials, have coloured Vesta's surface in a broad swath around its equator.
Pothole-like features mark some of the asteroid's surface where the volatiles, likely water, released from hydrated minerals boiled off. While Dawn did not find actual water ice at Vesta, there are signs of hydrated minerals delivered by meteorites and dust evident in the giant asteroid's chemistry and geology. The findings appear today in the journal Science.
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Dawn probe leaves Asteroid Vesta

The US space agency's Dawn satellite has left the giant Asteroid Vesta after 13 months of study.
A signal from the probe confirming that it had escaped the gravitational bounds of the 530km-wide rock was received by Nasa on Wednesday.
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Space missions trigger map wars

When NASA's Dawn spacecraft departs from Vesta on 26 August, it will have mapped the second-most-massive object in the Solar System's asteroid belt in unprecedented detail, revealing a diverse, planet-like body with sheer cliffs and deep craters.
But don't ask for the latitude and longitude of those features. The mission team is embroiled in a dispute with the International Astronomical Union (IAU) in Paris over which coordinate system to use, and where to place the prime meridian from which longitude will be measured. At the moment, the groups each have their own meridians, separated by 155°: nearly half a world.
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Title: Delivery of Dark Material to Vesta via Carbonaceous Chondritic Impacts
Authors: Vishnu Reddy, Lucille Le Corre, David P. O'Brien, Andreas Nathues, Edward A. Cloutis, Daniel D. Durda, William F. Bottke, Megha U. Bhatt, David Nesvorny, Debra Buczkowski, Jennifer E. C. Scully, Elizabeth M. Palmer, Holger Sierks, Paul J. Mann, Kris J. Becker, Andrew W. Beck, David Mittlefehldt, Jian-Yang Li, Robert Gaskell, Christopher T. Russell, Michael J. Gaffey, Harry Y. McSween, Thomas B. McCord, Jean-Philippe Combe, David Blewett

NASA's Dawn spacecraft observations of asteroid (4) Vesta reveal a surface with the highest albedo and colour variation of any asteroid we have observed so far. Terrains rich in low albedo dark material (DM) have been identified using Dawn Framing Camera (FC) 0.75 µm filter images in several geologic settings: associated with impact craters (in the ejecta blanket material and/or on the crater walls and rims); as flow-like deposits or rays commonly associated with topographic highs; and as dark spots (likely secondary impacts) nearby impact craters. This DM could be a relic of ancient volcanic activity or exogenic in origin. We report that the majority of the spectra of DM are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta. Using high-resolution seven colour images we compared DM colour properties (albedo, band depth) with laboratory measurements of possible analogue materials. Band depth and albedo of DM are identical to those of carbonaceous chondrite xenolith-rich howardite Mt. Pratt (PRA) 04401. Laboratory mixtures of Murchison CM2 carbonaceous chondrite and basaltic eucrite Millbillillie also show band depth and albedo affinity to DM. Modelling of carbonaceous chondrite abundance in DM (1-6 vol%) is consistent with howardite meteorites. We find no evidence for large-scale volcanism (exposed dikes/pyroclastic falls) as the source of DM. Our modelling efforts using impact crater scaling laws and numerical models of ejecta reaccretion suggest the delivery and emplacement of this DM on Vesta during the formation of the ~400 km Veneneia basin by a low-velocity (<2 km/sec) carbonaceous impactor. This discovery is important because it strengthens the long-held idea that primitive bodies are the source of carbon and probably volatiles in the early Solar System.

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Tarpeia Crater

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RE: Vesta

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Asteroid collision that spawned Vesta's asteroid family occurred more recently than originally thought

A team of researchers led by a NASA Lunar Science Institute (NLSI) member based at Southwest Research Institute has discovered evidence that the giant impact crater Rheasilvia on Asteroid (4) Vesta was created in a collision that occurred only about 1 billion years ago, much more recently than previously thought. This result is based on the analysis of high-resolution images obtained with the Dawn spacecraft, which entered orbit around Vesta in July 2011.
In addition to creating the crater, the impact is believed to have launched a large number of fragments into space, some of which later escaped the main belt and possibly hit the Earth.
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Asteroid Vesta is 'last of a kind' rock

Vesta is the only remaining example of the original objects that came together to form the rocky planets, like Earth and Mars, some 4.6 billion years ago.
This assessment is based on data from the Dawn probe which has been orbiting the second largest body in the asteroid belt for the past 10 months.
The findings from the Nasa mission are reported in Science magazine.
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