Scientists who for the first time tracked an asteroid on a collision course with Earth, and watched as it exploded in the atmosphere, have now picked up some of the remnants on the ground.

The discovery and analysis of the meteorites, reported in Thursday’s issue of Nature, give scientists solid data on the composition of meteorites that originate from at least one type of asteroid, known as F-class.

Millions of asteroids, mostly small, whirl around the solar system, and over the years people have picked up tens of thousands of meteorites, the surviving rock fragments of asteroids that collide with Earth.

“But we don’t know where a single one of them comes from,” said Michael E. Zolensky, a cosmic mineralogist at the Johnson Space Center in Houston, during a NASA-sponsored news conference on Wednesday.