How do we know that some meteorites are from Mars?

When it comes to Martian meteorites, we haven't returned any samples thus far. However, the Viking and Pathfinder probes have provided enough data to justify this conclusion. Some Martian meteorites were found to contain trapped gas-inclusions that perfectly match the composition of the Martian atmosphere, but are distinct from our own. Several other characteristics are consistent with a Martian origin for these rare meteorites.

About Martian meteorites:

On March 31 1995, the New york Times and Science magazine reported what had long been suspected: a meteorite from Nigeria named Zagami was indeed a piece of the planet Mars ! A analysis of Zagami revealed that gas trapped within its matrix matched the signature of thé Martian atmosphere ( as determined by Viking lander in 1976 ). Today thirteen meteorites, are classified martian meteorites. Three distincts subgroup under the common name SNC meteorites (after Shergotty, Nakhla, and Chassigny). These martian meteorite subgroups are distinguished on the basis of mineralogy, but they all share isotopic signatures, petrologic characteristics. Except for the famous ALH84001, the relatively young crystallization ages (less than 1.4 billion years for all martian rock and 4.5 billion for ALH84001) is surprising if compared to all others chondrite ( more than 4.6 billion years!). .

The shergottite subgroup is named after Shergotty, an achondrite which fell in India in 1865. Shergottites are pigeonite and augite-dominated basalts. Shergottites include the well known Zagami (Nigeria 1962) available for collectors sinces many years.

The nakhlite subgroup is named after Nakhla, an achondrite which landed in Egypt in 1911. Nakhlites are augite-rich achondrites. Nakhlites include also Lafayette (Indiana find) and Governador Valadares (Brazil find).

The chassignite subgroup is named after Chassigny, an achondrite which fell in France in 1815. Chassignites are olivine-rich achondrites. Until now no more chassignite were found, chassigny is the only chassignite !

**A search for Martian sediments. 1997LPI....28..381F 1.000 03/1997 A F Franchi, I. A.; Wright, I. P.; Pillinger, C. T. http://www.lpi.usra.edu/meetings/lpsc97/pdf/1634.PDF

Launch conditions for Martian Meteorites: Plagioclase as a shock pressure barometer. J. Fritz, A. Greshake,

and D. Stöffler, Institut für Mineralogie, Museum für Naturkunde, Humboldt Universität zu Berlin, Invalidenstraße

43, 10115 Berlin, e-mail: joerg.fritz.1@rz.hu-berlin.de

http://ifp.uni-muenster.de/spp1115/content/pub/PDF/LPSC34thAbstractFritzetal.2003a.pdf