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Martian meteorites, meteorites from Mars
Mars Meteorites (SNC Group)
The SNC's (Shergottite, Nakhlite, Chassignite) have always been the most desired meteorites for collectors and are also some of the most valuable.
SNC Group Achondrites - Mars Meteorites
The SNC group is named for three historic meteorite falls, Shergotty, Nakhla, and Chassigny, each representing a distinct rock type of a common parent body. Shergotty is a rather evolved basaltic rock, whereas Nakhla and Chassigny represent equally evolved plutonic cumulates. These unusual meteorites were initially classified with the HED group, but were subsequently comprised into a new group when their young crystallization ages were ascertained, and their unique oxygen isotope fractionation line was determined. Obviously, the SNCs represent a distinct group of highly evolved achondrites with some most unusual features.
With crystallization ages of just 0.15 to 1.35 billion years, these meteorites show to be very young compared to all other achondrites. The HED members show absolute ages of about 4.5 billion years, and even the youngest lunar basalts exhibit relatively ancient crystallization ages of about 2.8 billion years. Obviously, the SNCs formed on a parent body that has retained its igneous activity until very recent times, suggesting that the source of these strange rocks is a planet. The mystery of their origin was finally solved in 1985 after the discovery of trapped gas inclusions inside the shergottite EETA 79001. Based on data obtained by the Viking probes, which landed on Mars in 1976, the composition of this trapped gas is identical to the martian atmosphere, suggesting that the SNCs have their origin on Mars. Today, after more Mars missions, and comparisons, it has been proven beyond doubt that the SNCs are indeed genuine samples of our red neighbor, the planet Mars, and consequently they are also known as Mars meteorites. The latest proof of origin has been delivered by Mars Exploration Rover "Opportunity": the rover studied a rock dubbed "Bounce" at Meridiani Planum with mineral compositions very similar to EETA 79001, providing another strong link between Mars, and the meteorites of the SNC group.
Martian meteorites are of major scientific importance because they represent the only known samples of another planet available for research. From a geological point of view, they are most intriguing, but more importantly, they provide tantalizing clues to the question of the possibility of life on other planets. Not only do most martian meteorites contain minerals that have been altered by the presence of water, but some also contain traces of amino acids, the fundamental building blocks of life. Moreover, some even contain microscopic structures that have been interpreted as microfossils by some researchers. However, it is hard to rule out a possible terrestrial contamination of these samples, and therefore the evidence of microfossils has been vigorously challenged by other scientists claiming an inorganic formation process being responsible for these odd structures. The debate about whether there is, or has ever been, life on Mars probably won't end until new Mars missions return their pristine samples of rocks and soil. Only then will we be able to make comparisons, under appropriate sterile conditions, to the Mars meteorites in our collections.
If we exclude all probable pairings, 34 different Mars meteorites have been recovered to date, comprising a total weight of about 94 kg, with about 66 kg recovered from out of Antarctica. Based on their mineral compositions, the Mars meteorites are further divided into six related subgroups: basaltic shergottites, olivine-phyric shergottites, lherzolitic shergottites, nakhlites, chassignites, and orthopyroxenites, the latter subgroup consisting of just one single member.