Science: More than 400,000 asteroids have been identified in the solar system to date. These objects are thought to be the surviving remnants of the planetesimals that formed the planets about 4.6 billion years ago. The ages and mineralogical characteristics of these planetesimals can be estimated through high-precision laboratory analyses of the compositional and isotopic properties of meteorites, of which more than 30,000 samples exist.

Until now there has been no way to estimate when an asteroid formed, other than assuming that its age was similar to that of most meteorites. In the 25 April Science there is a new paper that present results of a remote spectroscopic study to show that a number of asteroids are enriched in the oldest known objects in the solar system (calcium-aluminum inclusions or CAIs), thereby making them the most ancient asteroids currently known.