Vesta, the Planet That Could've Been

Vesta, the Planet That Could've Been

Vesta vs. nearby asteroids. Credit: Science/AAAS

For the last year or so, NASA's Dawn mission has been hanging around near Vesta, the second-larges object in the Asteroid Belt that lies between Jupiter and Mars (trailing only Ceres, which is a member of Pluto's dwarf planet club.) A smattering of researchers from the Dawn team published their findings about the Arizona-sized asteroid in the journal Science today.

The first thing they learned about Vesta: Yes, it has been bombarding the Earth. OK, not directly, but the scientists showed they were correct in believing the big asteroid is the so urce of a particular class of meteoritesâ€"the howardite-eucrite-diogenite (or HED) meteorites, which make up about 1 of every 20 meteorites that hit our planet.

The reason there are so many Vesta-sourced rocks around to strike the Earth, the researchers say, is that as least two decently sized asteroids pummeled Vesta perhaps one to two billion years ago. One of the new studies released today describes two overlapping craters at the south pole of Vesta that combine to create a depression more than 300 miles across. The Washington Post quotes a team member as estimating that enough material to fill 400 Grand Canyons broke lose during the smash-up.

The final big finding is a confirmation: As many researchers had thought, Vesta was on the road to planethood during the earliest days of the solar system. Astronomers put forth this idea after studying the HED meteorites, whose compositions suggested Vesta was no ordinary asteroid. Data from Dawn also have shown that Vesta has an iron core and a surface with a geological history that's more like the terrestrial planets than the asteroids.

Alas, Vesta was the victim of a bully. Once Jupiter formed, the thinking goes, its immense gravity pulled on the objects like Vesta inhabiting the area that's now the Asteroid Belt, preventing them from coalescing into a single planet.

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