The predominance of young meteorites in the Mars collection is not only a disappointment to scientists who yearn for more clues about the planet's geology, it is starting to get downright puzzling. If the vast majority of Mars' surface is billions of years old, then it seems reasonable to expect that a similarly large proportion of meteorites from the planet would reflect this age. A tidy explanation, Borg said, if it didn t conflict with information about the length of time that each of the meteorite samples spent in space. Work by several other researchers shows that explaining the origin of these rocks is not so easy. That is a measure of how long the rocks spent in transit between Mars and Earth.
Cosmic rays radiate from the sun.
They are extremely energetic and highly destructive. When they hit material in space, they cause nuclear interactions that leave behind radioactive products, called radionuclides. Both rock and thick atmospheres provide shields against cosmic rays. Once they reached Earth they were protected again. By counting the amount of radionuclides in a given meteorite, scientists can determine how long the rock spent in space.