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Asteroid Vesta (also known as 4 Vesta) is the second largest object in the asteroid belt between Mars and Jupiter. The largest, Ceres, is four times larger than Vesta. At this time it is not considered a dwarf planet, but the classification will be re-evaluated when NASA’s Dawn spacecraft orbits the asteroid in 2011. Vesta is the first stop for the Dawn on what will be a historic mission to orbit two planetary bodies in one mission.
Vesta was first discovered on March 29, 1807 by German astronomer Heinrich Wilhelm Olbers. Vesta measures 578 km by 458 km and has a mass of 2.67 x 1020 kg. It’s possible that it has enough mass to pull itself into a sphere, but scientists haven’t gathered enough data to confirm this yet. This lack of confirmation is the main reason Vesta isn’t considered a dwarf planet. Vesta rotates on its axis every 5.342 hours and has an axial tilt of 29º. The surface temperature ranges from a frigid -188ºC (85 K) to a manageable -18ºC (255 K).
Although Dawn hasn’t taken its closeup images yet, Hubble images have revealed a world with ancient lava flows. A gigantic impact basin that is so deep it exposes the asteroid’s subsurface, or mantle, is at the South pole. The mantle is thought to be 10 km below the asteroid’s surface. Something enormous must have crashed into Vesta to create this deep scar. There are indications that lava once flowed on Vesta; a contradiction of the belief that asteroids are cold, dead rocks in space.
A large number of meteorites are thought to be parts of Vesta (vestian). Because of this, Vesta is one of only five solar system bodies that we have samples of. The others being Earth, the Moon, Mars, and the comet Wild 2.
Vesta has a brightness magnitude of +5.4 to +8.5. On any pollution free night it can be seen with binoculars. It has also been seen with the unaided eye on several occasions.
Vesta may not present itself as the largest body in the heavens, but it is one of the most interesting. Its contradiction of the notion that all asteroids were cold rocks and its relatively fast axial rotation make for some very interesting debate. The question of whether it should be called a dwarf planet could be resolved fairly quickly after the Dawn space mission orbits the asteroid. All in all, this is a very cool space object.
We have written many articles about Vesta for Universe Today. Here’s an article about Dawn’s current trajectory towards Vesta, and here’s an article about a strange micrometeorite found in Antarctica – a fragment of Vesta?.