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Vesta’s Formation History? It’s Complicated.

Image of Vesta's south pole acquired by Dawn on July 18, 2011

Image of Vesta’s south pole acquired by Dawn on July 18, 2011

Just when scientists thought they had a tidy theory for how the giant asteroid Vesta formed, a new paper from NASA’s Dawn mission suggests the history is more complicated.

If Vesta’s formation had followed the script for the formation of rocky planets like our own, heat from the interior would have created distinct, separated layers of rock (generally, a core, mantle and crust). In that story, the mineral olivine should concentrate in the mantle.

However, as described in a paper in this week’s issue of the journal Nature, that’s not what Dawn’s visible and infrared mapping spectrometer (VIR) instrument found. The observations of the huge craters in Vesta’s southern hemisphere that exposed the lower crust and should have excavated the mantle did not find evidence of olivine there. Scientists instead found clear signatures of olivine in the surface material in the northern hemisphere.

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Dawn Makes an Elemental Discovery on Vesta

Hydrogen “hot spots” are shown in this color-coded image of Vesta, a single frame from an animation. Red indicates the greatest abundance.

In what could be called a “eureka” moment for Dawn researchers and planetary scientists alike, hydrogen has been found on the surface of Vesta, a 550-km (340-mile) -wide protoplanet and the second most massive world in our Solar System’s main asteroid belt. The elemental discovery was made with the Gamma Ray and Neutron Detector (GRaND) instrument on board NASA’s Dawn spacecraft, which just completed its 13-plus-month-long mission orbiting Vesta and is now heading for Ceres.
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Is Vesta a Planet Among Asteroids?

After nearly 5 months in orbit around Vesta, NASA’s Dawn spacecraft has returned some incredibly detailed data about the composition and structure of what was once surely considered an asteroid. But now scientists are starting to have second thoughts about what exactly Vesta is… is it really an asteroid? Or is it more like a planet? Some signs seem to indicate the latter, which (once again) raises the question of what classifies a planet and, more importantly, what comprises the ever-surprising family of worlds we call our solar system?

“Vesta is not a simple ball of rock. This is a world with a rich geochemical history.”

– Chris Russell, Dawn mission principal investigator, UCLA

Colorful cross-sections of diogenite meteorites recovered from Antarctica, believed to originate from Vesta. Image Credit: Hap McSween (University of Tennessee), and Andrew Beck and Tim McCoy (Smithsonian Institution)

Watch the video above from Science@NASA to learn more.

Vesta resides in the main asteroid belt between the orbits of Mars and Jupiter and is believed to be the source of many of the meteorites that fall to Earth. The Dawn spacecraft successfully entered orbit around Vesta on July 16, 2011.

After investigating Vesta for a year Dawn will then leave orbit and move on to Ceres, the largest asteroid in the solar system, once considered a planet. Once successful Dawn will be the first spacecraft to orbit two different worlds.

Pay a Visit to Vesta

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Here’s a great video released by JPL taking us on a virtual tour of the asteroid Vesta, from the point of view of NASA’s Dawn spacecraft. It’s a shape model of Vesta, mapped with actual images acquired by Dawn during its approach and orbit of the 550-km (340-mile) -wide protoplanet.

Once little more than a fuzzy point of light to astronomers, Dawn has revealed Vesta to be quite a fascinating little world, with many unique and unexpected landforms like mountains, steep scarps, long grooves, scattered light and dark splotches and curious clusters of “wormlike” scratches. And all this in just three months of orbit… not too shabby!

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A Snowman on Vesta

A set of three conjoined craters on Vesta

Aptly nicknamed the “Snowman”, these three craters were imaged on August 6, 2011 by NASA’s Dawn spacecraft in orbit around the protoplanet Vesta. Located on Vesta’s northern hemisphere, the craters were first visible to researchers on July 23.

Dawn has been in orbit around Vesta for one month now and has already returned many amazingly detailed images of the massive asteroid’s surface. It’s hard to believe that until these past few weeks all we had ever seen of this world were blurry images, and now we’re nicknaming surface features! Now that the science portion of the mission is under way, new images like this are coming in almost daily.

You can follow Dawn’s progress on the mission site here.

Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. (Edited by J. Major.)

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