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.
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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The video reveals the dappled, variegated surface of the giant asteroid Vesta, the second most massive object in the main asteroid belt. 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.
Bright craters, dark craters… craters shaped like butterflies… they’re all represented here in a panorama made from images acquired by NASA’s Dawn spacecraft, currently orbiting the 330-mile-wide asteroid Vesta.
I stitched two images together (using a third for gap fill-in) that were originally acquired by Dawn’s framing camera in October 2011 and released last week. This shows just some of the many surface features found on this ancient world.
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
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.