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Could giant asteroid Vesta actually be a planet?

Illustration for article titled Could giant asteroid Vesta actually be a planet?

For years, scientists have been calling Vesta an asteroid. Granted, it's a big asteroid — at 330 miles across, it's the second biggest in the solar system — but NASA's Dawn spacecraft recently got its closest look at Vesta yet, and according to Dawn's principle investigator Christopher Russel, astronomers have been finding it hard not to refer to the asteroid as a planet.

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Of course, the odds of the International Astronomical Union convening to name Vesta a planet (the same way they met in 2006 to reclassify Pluto as a dwarf planet) are basically zero. So instead, astronomers have taken to describing the massive asteroid as "transitional." But what's with all the confusion in the first place?

Long story short: Vesta resembles a planet. And not just any planet; Vesta is home to a lot of features typically associated with terrestrial bodies like Earth. The ratio between its topography (the elevation of its various surface characteristics) relative to its radius, for instance, is more like a rocky planet's than an asteroid's.

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It also harbors something called impact melt, the remnants of at least one collision event so powerful, it actually liquified portions of Vesta's surface — something never observed on an asteroid before. Researchers think that this impact melt, which would have flowed readily across Vesta's face following an extraterrestrial collision, may explain why they've found no evidence of volcanic activity in the form of lava flows. Scientists are convinced that Vesta's past was characterized by long periods of volcanism, but it's possible that any sign of volcanic activity has been hidden by collisions and impact melt.

"[It's] because of all the impact processing over Solar System history," explained Arizona State's Dave Williams to BBC News. "It has destroyed all the evidence."

The Dawn spacecraft is scheduled to continue orbiting Vesta until July of this year, when it will set a course for Ceres, the largest asteroid in the Solar System. Ceres is significantly larger than Vesta; at close to 600 miles in diameter, it actually qualifies as the smallest of the dwarf planets. It'll be very interesting to see if its surface features are as stereotypically "planet-like" as Vesta's.

Read more about Dawn's latest views of giant asteroid Vesta over on BBC News.
Top image via NASA

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DISCUSSION

Fall Hammer

I remember asking what a planet was as a kid and I was told that anything with a recognizable orbit, and spun on its own axis was a planet and all others were moons (i.e. orbit larger bodies) or asteroids, I still don't understand why we don't clasify Ceres and Vesta as planets and also Pluto still, and just have 12 planets and maybe counting.