The European Space Agency's Rosetta spacecraft flew by the asteroid Lutetia in July 2010 and scientist have finished analyzing the data gathered during the brief encounter, a release from ESA headquarters in Paris said Thursday.
The analysis confirms their initial impression of Lutetia as an old, primitive "mini-world," the release said.
Parts of Lutetia's surface are around 3.6 billion years old, and show their age by the large number of impact craters.
Some impacts must have been so large they broke off whole chunks of Lutetia, gradually sculpting it into the battered wreck we see today, astronomers said.
"We don't think Lutetia was born looking like this," Holger Sierks of the Max Planck Institute in Lindau, Germany, said. "It was probably round when it formed."