How could scientists affirm that a meteorite comes from Mars and not from another source ? This is a probability or an absolute certainty ? How much percent ?
Essentially, a chemical and mineralogical comparison is made between the meteorite and samples taken from the Martian surface and atmosphere - particularly from the article The SNC meteorites are from Mars (Treiman et al. 2000, Planetary and Space Science, vol. 48, pp. 1213-1230), that states:
Figure 1 of that article shows a comparison of relative abundances of isotope from the Martian atmosphere and the Martian meteorites found on Earth.