Large asteroid Vesta once had molten core, magnetic field

Ars Technica » Scientific Method 2012-10-23

Despite its skewed appearance, Vesta seems to have many features in common with planets.

Models of our solar system's formation suggest that the inner rocky planets were built in stages, as small objects combined to create planetesimals, which merged to protoplanets. Collisions among these built the planets we're familiar with. Although this process happened over four billion years ago, it may still be possible to understand this era. Some evidence implies that Saturn's moon Phoebe may be a planetesimal, while some of the largest asteroids appear to be protoplanets. By studying them, we can look back to the earliest stages of our Solar System's history.

Thanks to NASA's Dawn mission, we recently got a better look at one of these protoplanets, called Vesta. The spacecraft's visit revealed a surprising amount of volatile material and features that suggest the planet's interior was once sufficiently hot for it to become differentiated, with different materials layered based on their density. Now, a piece of Vesta that has fallen to Earth suggests that not only was the interior once molten, but it produced a spinning dynamo that generated a magnetic field.

One of Vesta's most dramatic features is a large crater on its south pole, where an impact gouged a huge chunk out of the asteroid. This impact has ensured that Vesta populated the inner solar system with plenty of rocks, some of which have struck the Earth as meteorites. Based on their chemical similarities, the HED (howardite–eucrite–diogenite) meteorites appear to have originated on Vesta.

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