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Vesta’s cratered face, as seen from Dawn; the spacecraft (illustrated here) is orbiting 3,200 miles above the surface. NASA/JPL-CALTECH

In the spacious bit of space between Mars and Jupiter two grey, dwarfed and discouraged rocky bodies orbit the sun. Filled with promise and ambition 4.5 billion years ago, these two wannabe planets have long since had their hopes dashed by our gassiest and most gigantic gas giant: Jupiter.

View of Ceres from Keck Observatory. Image credit: NASA/JPL

The two little buggers I’m referring to are Ceres and Vesta, and together they make up 40% of the total mass of the asteroid belt that divides our rocky inner planets from the moon-hoarding, obese gas guys that lazily mope their way around the sun in outer orbit.

Ceres and Vesta are not your run-of-the-mill asteroids though; for a few good reasons, they’re far more interesting: (1) Ceres is in the same weight class as Pluto and Vesta is only a little smaller (little being relative here). Ceres even had its classification bumped from asteroid to dwarf planet six years ago. (2) Both bodies are influenced by Jupiter’s gravitational pull just enough to have kept them from merging with the inner planets, but far enough that they weren’t flung out into oblivion. (3) Given that they were likely in the process of becoming planets themselves when Jupiter pulled them out of harms way, Ceres and Vesta’s composition should serve as a snapshot of the early stages of planet formation and hopefully shed some light on how Earth came to be.

The coolest and most interesting thing about Ceres and Vesta though, is that we’re actively exploring them. In 2007 the Dawn spacecraft hitched a ride on a Delta II rocket and made its way to Vesta’s orbit, arriving last summer and streaming data to NASA scientists back home. Surprisingly, the asteroid’s composition shares more similarities to Earth’s than expected.

In August the satellite left Vesta’s orbit and began its two year journey to Ceres. This is super exciting, and with all the data that’s going to be coming our way in the next few years, it’s definitely a mission worth keeping an eye on.

Dawn baseline interplanetary trajectory for primary mission. Dashed lines represent orbits of Mars, Vesta, and Ceres.

For more information check out the article on DiscoverMagazine.com.