page_title: Martian meteorite
section_title: Age estimates based on cosmic ray exposure
hierarchical_section_title: Martian meteorite / Origin / Age estimates based on cosmic ray exposure
caption_attribution_description: English: A Martian meteorite crafted into a small pendant and suspended from a silver necklace.
context_page_description: A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, traversed interplanetary space, and finally landed on the Earth as a meteorite. as of April 2019, 266 meteorites have been identified as Martian, out of over 61,000 known meteorites. These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmospheric gases on Mars, which have been measured by orbiting spacecraft, surface landers and rovers. The term does not include meteorites found on Mars, such as Heat Shield Rock.
context_section_description: The amount of time spent in transit from Mars to Earth can be estimated by measurements of the effect of cosmic radiation on the meteorites, particularly on isotope ratios of noble gases. The meteorites cluster in families that seem to correspond to distinct impact events on Mars.
  It is thought, therefore, that the meteorites all originate in relatively few impacts every few million years on  Mars. The impactors would be kilometers in diameter and the craters they form on Mars tens of kilometers in diameter. Models of impacts on Mars are consistent with these findings.
  Ages since impact determined so far include
caption: A Martian meteorite crafted into a small pendant and suspended from a silver necklace.
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