SNC (shergottite, nakhlite, chassignite) achondrites are similar in many respects to terrestrial basaltic and ultramafic rocks. Several independent geochemical and petrological characteristics suggest that they formed on Mars. These include young (∼1.3 b.y.) crystallization ages, evidence for a magmatic history too complex for an asteroid, possibility of garnet in the source region, calculations of the magnitude of the gravity field necessary for crystal accumulation by settling, presence of trapped gases similar to the the Martian atmosphere, and other features consistent with what is known about Mars. However, the dynamical difficulties of ejecting meteorites from planetary surfaces are formidable.