The rock dust closely resembles material from bodies called chondritic meteorites from asteroids in the asteroid belt between Mars and Jupiter, they reported in the journal Science. Asteroids are fragments of ancient space rubble, made of rock and metal, that commonly orbit the sun in that belt.

Wild 2 is named for Swiss astronomer Paul Wild (pronounced Vilt), who found it in 1978. Its diameter is 3 miles and it orbits the sun every 6-1/2 years.

Stardust, launched in 1999, intercepted Wild 2 in 2004 in the vicinity of the asteroid belt, collecting dust particles from it. The spacecraft returned to Earth in January 2006 with a cargo of the tiny particles for scientists to study