Third largest and fourth brightest asteroid; it was discovered in 1807 by Heinrich Olbers and named for the ancient Roman goddess of the hearth. 4 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, heated by short-lived radio-isotopes. A deep impact crater 456 km wide (on a world itself not much over 500 km across!), visible to the Hubble Space Telescope, exposes 4 Vesta’s mantle.

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The theory is that, during the impact event, large chunks of matter were ejected from 4 Vesta to form smaller asteroids of similar composition – so-called Vestoids. Some of these bits of 4 Vesta subsequently entered near-Earth orbits, and are thought to be the sources of the howardites, eucrites, and diogenites.

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.

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