Martian meteorite
Martian meteorites are stony meteorites achondritische that originate from the planet Mars. The previously known Martian meteorites are also named after the three subgroups ( Shergottites, Nakhliten and Chassigniten ) SNC meteorites. Although the first SNC meteorite was found in 1815 in the village of Chassigny in France, most meteorites, researchers have recognized only since the early 1980s, the origin of Mars. However, this origin is not quite so clearly secured as the origin of meteorites from the moon, because so far there has been no mission to Mars, has brought the rock to compare.
Origin
Mars meteorite caused by larger asteroid impacts on Mars. Through the force of the impact Martian rocks is hurled into space. Some of these so liberated rocks reach the Earth as meteorites.
History of Research
As early as 1979 it was argued that the then-known SNC meteorites, unlike most other meteorites, can not come from asteroids. The measured crystallization age of the SNC meteorites was a maximum of 1.3 billion years and was of volcanic origin. Asteroids, however, are already relatively cooled shortly after its formation 4.5 billion years ago and since then show no volcanism. It was concluded then that other than Earth, Mars and Venus only come into question, as they still showed volcanism 1.3 billion years ago; Volcanic activity on Jupiter's moon Io in 1979 was not yet known.
The idea that the said meteorites could come from Mars, has prevailed until 1983. In an article in the journal Science was then shown that the isotopic abundance of argon in shock- melted glass inclusions corresponded to the measurements in Shergottites EETA79001 that was made by the Viking spacecraft in the atmosphere of Mars. Later, the frequencies of the other noble gases as well as carbon dioxide and nitrogen in these glass inclusions were determined, which is also consistent with the data from Viking.
In further studies of SNC meteorites also some inconsistencies were discovered, such as xenon isotopic abundances in the SNC meteorites Chassigny. However, these can be provided by the addition of noble gases from other sources, such as the Mars interior, explain. As a further indication of an origin from Mars is called in some SNC meteorites often the strong orientation of needle-shaped crystals. The alignment can be explained by the existence of a strong gravitational field of a body with at least the size of Earth's moon during the solidification of the meteorite material from the original magma. However, could, for example, convection currents of magma effect alignment of the crystals. Another strong indication that the origin of Mars has been provided by the Opportunity mission, where a bounce rock was discovered and investigated called Stone, the chemical composition of the basaltic Shergottites, especially EETA79001 is like.
Subdivisions
The Martian meteorites are divided as follows:
- SNC meteorites (clan )
- Shergotite (Group )
- Nakhlite (Group )
- Chassignite (Group )
- Orthopyroxenreiche Martian meteorites ( ALH 84001 Only )
- Basaltbrekzien from Mars (Only NWA 7034 )
Discussion of life remains
In 1996, David S. McKay and his collaborators found in the Martian meteorite ALH 84001 structures that was found in Antarctica in 1984, which they interpreted as signs of fossil bacteria. Their arguments for traces of fossil life in ALH 84001 were also critically commented:
- Structures in electron micrographs were interpreted as fossilized bacteria. However, it is argued that these structures could also be artifacts of the recording technique used. Moreover, the size of the structures in the range of only a few nanometers, much smaller than conventional ground bacteria. Although nanobacteria were reportedly discovered on Earth, but this is so far controversial.
- Karbonateinschlüsse which magnetites in a form in which it is produced to the earth bacteria. However, it has so far not be excluded that this magnetite can not be produced by non-biological processes.
- Polycyclic aromatic hydrocarbons (PAH, of Engl. Polycyclic Aromatic Hydrocarbons ) within the carbonates, which may arise from the decay of bacteria. Again, it is difficult to show that there are no non-biological processes, which generates the same pattern of PAHs as it was found in the ALH 84001.
The theses of McKay and his co-authors are controversial to this day. It leftovers were now also in two other Martian meteorites, Shergotty and Nakhla, found from past lives.