“Vesta is special”

Having arrived at the 530km-wide giant asteroid Vesta in July last year, Nasa’s Dawn Mission scientists have published some of their findings in Science magazine.  As the BBC’s spaceman, Jonathan Amos, notes

They confirm that Vesta has a layered interior with a metal-rich core, just as Earth, Mars, Venus and Mercury do.

Using information about the shape of the asteroid and its gravity field, scientists can even say something about the likely size of this core.

The Dawn team calculates it to be about 220km (135 miles) across, representing about 40% of the radius of Vesta, or roughly 18% of its total mass.

They have also calculated the age of two major crater basins on the protoplanet, such as Rhea Silvia below, to be surprisingly young.

From the JPL News press release

“We know a lot about the moon and we’re only coming up to speed now on Vesta,” said Vishnu Reddy, a framing camera team member at the Max Planck Institute for Solar System Research in Germany and the University of North Dakota in Grand Forks. “Comparing the two gives us two storylines for how these fraternal twins evolved in the early solar system.”

Dawn has revealed details of ongoing collisions that battered Vesta throughout its history. Dawn scientists now can date the two giant impacts that pounded Vesta’s southern hemisphere and created the basin Veneneia approximately 2 billion years ago and the Rheasilvia basin about 1 billion years ago. Rheasilvia is the largest impact basin on Vesta.

“The large impact basins on the moon are all quite old,” said David O’Brien, a Dawn participating scientist from the Planetary Science Institute in Tucson, Ariz. “The fact that the largest impact on Vesta is so young was surprising.”

Here’s an animation of the mapped gravity field of the giant asteroid Vesta closely matching the surface topography. [Video from JPLNews]

And a virtual flight aboard Dawn over the giant asteroid. [Video Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA]

And if you want more information on what Dawn found at Vesta, here’s the Nasa TV science briefing on 10 May.

Dawn will remain at Vesta until 26 August when it will start the next leg of its journey – Destination [the even larger protoplanet (dwarf planet)] Ceres, ETA 2015.

Pete Baker