Planet Seed Chronicles of Lutetia

Asteroid 21 Lutetia isn't just another pebble in a big pile of space rocks. Scientists now think it is a leftover planetary seed, booted into the main belt by the planetary bullies growing around it.

Lutetia and its asteroid cousins are thought to be relics from the early solar system, rocky fossils that have recorded a history of the solar system's early days in their pits and fractures. In July 2010, the European Space Agency's Rosetta spacecraft flew within 3,200 kilometers of Lutetia, peered at the asteroid and attempted to read its stony story.

Using data gathered by Rosetta, three reports describe Lutetia's surprising composition and terrain. They appear in the Oct. 28 Science.

“If you have visited one asteroid, you have not visited them all,” says Lindy Elkins-Tanton of the Carnegie Institution for Science in Washington, D.C. “We can still learn some amazing new things about planetesimals, primitive materials, solar system dynamics and [asteroid] composition.”

Data suggest that Lutetia is what's known as an enstatite chondrite a rare form of asteroid that makes up around 2 percent of the meteorites that have fallen to Earth. “It's pretty uncommon,” says planetary scientist and study author Pierre Vernazza of the European Southern Observatory. “Our understanding is that this kind of meteorite is the starting composition of the terrestrial planets, from Mercury to the Earth.”