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Vesta (minor planet 4)
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| Hubble image of Vesta taken in 1996. A 456-km wide crater is visible at the bottom of the image. Credit: Ben Zellner, Georgia Southern University; Peter Thomas, Cornell University; NASA
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| Hubble image of Vesta taken in 2007. Credit: L. McFadden/NASA/ESA
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Vesta has a basaltic surface composition and an average density not much less than that of Mars. Evidently lava once flowed here indicating that the interior was at one time molten. A deep impact crater 456 km wide (on a world itself not much over 500 km across!), visible to the Hubble Space Telescope, has exposed the mantle beneath Vesta's outer crust, showing that Vesta has been differentiated into layers, like the terrestrial planets, and so must have had an internal heat source in addition to the heat released by long-lived radio-isotopes.
Not only can we peer (albeit dimly, for the moment) at Vesta's interior, but we have, scientists believe, quite a few samples of Vesta here on Earth. These consist of the so-called HED group of meteorites – the howardites, eucrites, and diogenites – which have spectral and geological fingerprints linking them to Vesta and to each other. But it's very unlikely that the HED stones came from Vesta directly. Vesta is located in a part of the main asteroid belt that makes it almost impossible for it to send meteorites to us. So there are probably intermediate asteroids, which were once part of Vesta, located in more favorable orbits that provide delivery. This theory has been bolstered by the discovery that the asteroid 1929 Kollaa, based on its reflectance spectrum, was once a part of Vesta, and, moreover, that it moves in an orbit from which meteorites could much more easily be launched Earthward.
The Dawn spacecraft will visit Vesta in 2011, before moving on to an encounter with the largest asteroid in the solar system, Ceres, in 2015. In preparation for the arrival of Dawn at Vesta, new images of the asteroid were taken by the Hubble Space Telescope in 2007. These show features as small as 60 km across, revealing variations in brightness and color across the asteroid's surface, some of which might be due to lava flows from ancient volcanic eruptions. As on the Moon, the darker regions might be basins that filled with lava that later solidified. The images obtained in 2007 show the giant crater on Vesta from the side, rather than face-on, and a bump that may be a peak at the center of the crater.
| Diameter | 525 km |
| Density | 3.3 g/cm3 |
| Spectral class | V |
| Rotational period | 5 hr 21 min |
| Semimajor axis | 2.361 AU |
| Perihelion | 2.149 AU |
| Aphelion | 2.574 AU |
| Eccentricity | 0.090 |
| Inclination | 7.13° |
| Period | 3.63 years |
Related category
• NOTABLE ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS
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