Meteorites from the planet Mars are my favourite group of all known meteorites. I've had a positive relationship with the planet Mars since I was a kid playing the computer game DOOM with my father, which is set on the planet Mars and its moons. Of course, the fact that my favourite colour has always been orange probably explains everything.
I look forward to the moment when the existence of ancient life on the planet Mars is confirmed. You may say that's nonsense, there is no life on Mars and has never been. I believe it, and I think the evidence is imprinted in the planet's mantle in the form of fossils. Mankind has made great strides in the exploration of Mars and there are now several robotic instruments operating on the surface of the planet that regularly send scientifically very valuable information back to Earth. I think that when we get humans and heavier equipment to Mars, humanity will discover the first Martian fossil.
About the planet Mars
Mars is the fourth planet of the solar system, the second smallest planet in the system after Mercury. It was named after the Roman god of war, Martius. It is a terrestrial planet, i.e., with a solid rock surface covered with impact craters, tall volcanoes, deep canyons, and other formations. It has two irregularly shaped moons called Phobos and Deimos.
The two firsts
Olympus Mons (Mount Olympus) is the highest known mountain in the solar system, located on the surface of Mars in the northwestern part of the Tharsis region. It is a classic shield volcano, with multiple calderas at its summit. It towers 27 km above Mars' zero altitude (roughly 21.5 km above the gravitational surface of Mars.
Valles Marineris (Valley of the Mariner) - named after the Mariner 9 spacecraft that first produced an image of it in 1971, is the largest known canyon system in the solar system located on the planet Mars. The Marineru Valley winds across more than one-sixth of the circumference of the planet's equator, east of the vast volcanic-tectonic region of Tharsis. The average width is about 200 km, but can reach up to 500 km in places. The slopes cut down to depths of up to 10 km.
How does Martian material reach the Earth?
The distance between Earth and Mars varies by tens of millions of kilometres. This raises a legitimate question - how does Martian material get to Earth? At first glance, however, this puzzling question has a logical explanation.
If I try to outline the main events that must occur for the Martian material to reach us, it is necessary for the material to split off from the home planet at very high speed, not evaporate in the atmosphere, and overcome the gravitational field of the home planet. If all these basic criteria are met, it is "just" enough to reach the planet Earth, collide with it and not evaporate a second time in the atmosphere of our planet. This implies that the ejected material must have sufficient size to be partially lost at least twice during its journey. It must also not collide with all sorts of space objects on its way.
Of course, I don't think that the path of all Martian meteorites to Earth is straightforward, imagine for example the interplay of several random changes of direction, without which the material would have missed planet Earth by thousands of kilometres. Anyway, back to the origin of the whole event. How does the material get ejected from the surface of Mars at high velocity? The answer is simple - a collision with a large enough celestial body.
Types of Martian meteorites
Martian meteorites belong to a group of differentiated achondrites and are quite young on a cosmic scale. They formed only 1.3 billion to 170 million years ago. Meteorites originating from the planet Mars are referred to as SNC. The abbreviation is derived from the locations where the three main representatives of this group of meteorites were found.
- Shergotty - India, 25 August 1865, 5 kg
- el-Nakhla - Egypt, 28 June 1911, 10 kg
- Chassigny - France, 3 October 1815, 4 kg
Initially, it was only clear that SNC meteorites were of volcanic origin and came from a body that was relatively recently volcanically active.
Approximately 82 percent of Martian meteorites are Shergottites and related rocks containing mostly pyroxene, olivine, and maskelynite or plagioclase; minor oxides, phosphates, and sulfides.
Approximately 9 percent of Martian meteorites are Nakhlites containing mostly augite, olivine, and minor to accessory pigeonite, orthopyroxene, plagioclase, silica, titanomagnetite, ulvöspinel, rutile, magnetite, hercynite, chlorapatite, merrillite, pyrrhotite, pyrite, marcasite, and chalcopyrite.
Approximately 1 percent of the Martian meteorites are Chassignites containing ≥ 90 % olivine and minor orthopyroxene, pigeonite, augite, plagioclase, sanidine, chromite, chlorapatite, troilite, pentlandite, ilmenite, rutile, baddeleyite, caersutitic amphibole, biotite and phlogopite.
Approximately 7 percent of Martian meteorites are classified as polymict breccias. They consist of mixed lithologies and have various differences found in typical SNC Martian meteorites.
Several Pyroxenites have also been found among the Martian meteorites. The two main representatives are meteorite ALH 84001 (contains mostly orthopyroxene; minor chromite, maskelynite, augite, apatite, pyrite, and carbonate) and NWA 2646 (contains mostly pigeonite, augite, olivine, and maskelynite; minor oxides, phosphates, and sulfides).
Martian meteorites also contain many high-pressure phases produced during the ejection of Martian rock from the surface.
How were the Martian meteorites identified?
The breakthrough came when studying the Elephant Moraine 79001 meteorite, which was discovered in 1979 in Antarctica. A small amount of gas was discovered in the meteorite, trapped in bubbles formed when the lava solidified. The composition was chemically identical to the one discovered by the Viking probes in the atmosphere of the planet Mars. The Martian origin of SNC meteorites was not widely accepted until the 1980s.
The representation of Martian meteorites
Martian meteorites are a group of very rare meteorites. Their number is in the order of tenths of a percent among all meteorites that have fallen to Earth. The Chassignites group, representing about one percent of all Martian meteorites, is a handful of very rare meteorites. My collection boasts one Chassignite, namely Diderot, NWA 2737. The meteorite was found in 2000 in Morocco. Interestingly, it was considered a pseudo-meteorite for about 5 years. It is a strongly shock-affected cumulate dunite containing about 90% olivine, 5% CPX and 2% plagioclase. Due to shock metamorphosis, the olivine changed colour from green to blue-black.
Mgr. Radek Šrejbr, 11. 2. 2023