Vesta is the 2nd-largest Asteroid in the well known asteroid belt between the orbits of Mars and Jupiter. 525 Km in diameter, it is very big for an asteroid. If it was much bigger we would call it a dwarf planet.
The Dawn Spacecraft, launched in 2007, stopped by Vesta in 2011 and stuck with it until 2012 as it orbited the sun. We are still seeing the results of that rendezvous, and just recently NASA released a complete map of the surface features of Vesta.
It’s amazing to see so many interesting surface features on such a small world. Geologic processes from the early Solar System are seen suspended in time across millions of comets and asteroids that have remained untouched in 4.6 Billion years.
Another great map of Vesta gives us 3D perspective, also helping to explain why Vesta is not a planet. The lack of spherical shape prevents it from being promoted to a dwarf planet, but as you can see, it’s close.
If Vesta was a bit larger, it’s own gravity would pull it into a sphere. The largest Asteroid in the belt, Ceres, is almost twice as large as Vesta, and is spherical, giving it dwarf planet status. This is actually the next target for Dawn, and it is currently in transit, expected to arrive next year.
Why send spacecraft to asteroids? The same reason we landed the Philae spacecraft on the comet last week. We want to study the early Solar System so that we can learn about the building blocks that gave rise to the Earth and eventually, the life that saturates it.
Every mission is a small piece of the great puzzle of the Universe, and as we piece them together we gain an understanding of our own distant history, painting a picture of our existence.