Cosmic Ray Exposure Age

Exposure ages for subset of chondrites. Image Source: Figure 6.1, Meteorites, Hutchison, 2004

Time interval that a meteoroid was an independent body in space. In other words, the time between when a meteoroid was broken off its parent body and its arrival on Earth as a meteorite – also known simply as the “exposure age.” It can be estimated from the observed effects on a meteorite by bombardment by cosmic rays from the Sun and the rest of the Galaxy. As these cosmic rays strike the meteoroid in space, they produce both radioactive isotopes, such as 3He, 21Ne, and 38Ar, and stable isotopes. The longer a meteoroid has been exposed to cosmic rays, the more of these new isotopes are formed. Further  dating information comes from an analysis of the fission tracks (thin trails left in a substance by a fast-moving atomic nucleus) that cosmic rays cause. Exposure ages range typically from 1-100 Ma.

Some or all content above used with permission from J. H. Wittke.