Ingolf Baur: Is Vesta still struck by space rocks and asteroids today?
Ulrich Köhler: Of course it is, like any other body in the solar system. There is so much debris cruising in orbits around the sun so they will collide, but it is not so frequent as it was in the early two billion years of the solar system.
So that is the time where all the scars on Vesta actually come from, right?
Right. What we see on the surface of Vesta - most of it is two to four billion years old - so we look at the early time of the solar system, and that is what makes Vesta so interesting for us.
Why didn't Vesta for example grow into a planet like Earth?
There was not enough left over, so to speak. Because Jupiter is next to Vesta - well 'next' is relative - but Jupiter is so big and has such a big gravitational attraction that it prevents asteroids from glueing together to bigger asteroids.
So you had to grow really fast in the beginning of the solar system.
That is correct - the faster the better
Your institute actually developed the camera the took all these images. What have you found out lately?
Together with our friends in Katlenburg-Lindau here in Germany from the Max Planck Society we built this camera, and it is so beautiful what images returned from the mission. We could see an asteroidal surface in such detail as never before, so we know much more about the processes that formed the surface.
And what are the latest findings, actually?
The most important thing is probably that we realized that the asteroid was stuck by two very big impacts in its early time that almost disturbed and destroyed the asteroid. At the south pole we see a large impact base in the diameter of 500 kilometers. That is about the diameter of the asteroid, and this was such a collision that it almost destroyed the asteroid
Was it a fast hit?
That is not so sure. We think it was not such a fast hit as the asteroids that hit Earth and Mars in the early solar system with 50,000, 60,000, up to 100,000 kilometers per hour. Because we see structures at the equator that look as if an object hit the south pole and distorted the entire asteroid and made some grooves there that are geometrically perfectly aligned to the impact.
Now the Dawn space probe is actually on its way to Ceres. What do you expect there?
Ceres is a different asteroid, in fact, it is now a dwarf planet, so it is really a bigger solar system body. It is almost like a planet. It is a sphere with 1,000 kilometers diameter and so big that it has more internal heat, of course, and further distant from the sun, so it has more volatiles in its interior. We think there could be frozen ice under the surface - or it could be even on the surface - and there could even be some water in pockets under the surface of Ceres.
Water - does that also mean there could be life? Bacteria?
We won't exclude it, but of course there could be some organic compounds that are the precursors of life. That is likely, but whether there is life - I would not go so far.
Interview by Ingolf Baur