Tissint -Soil Science Martian Style

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Dr Sasha Verchovsky and “Finesse”. Dr Verchovsky works in the Open University’s Department of Physical Sciences and made extensive measurements of carbon and nitrogen isotopes in Tissint using a high-sensitivity and high-precision mass spectrometer called “Finesse”. Dr Verchovsky’s analyses were able to show that Tissint contains traces of Martian atmosphere, as well as soil-like material from the surface of the red planet. (image: Richard Greenwood)

The results of an international study, published today in Science, has found traces of material from both the surface and atmosphere of Mars in the Tissint Martian meteorite. The research team, which was led by Professor Hasnaa Chennaoui Aoudjehane from the Hassan II University, Morocco, included four members of the Open University’s Physical Science Department.

The meteorite fell to Earth in a fireball on 18th of July 2011 near Tissint, a Moroccan town along the Algerian border. As it is only the fifth witnessed fall of a Martian meteorite to have been recovered, the rock has provided a unique opportunity for researchers to expand their understanding of Mars. Previous Martian meteorites have suffered varying degrees of terrestrial contamination. In contrast, the Tissint meteorite is so fresh that it has been possible to detect evidence of components from both the Martian surface and atmosphere. The features observed in Tissint are broadly compatible with previous observations made by spacecraft sent to Mars by NASA and ESA.

A small fragment of Tissint (width ~ 2 cm). The black glassy material on the left corner is called fusion crust and formed during heating in the Earth’s atmosphere as the stone arrived from space. The dark material in the centre of the stone formed during an impact event on Mars, probably when the rock was ejected from the surface of the red planet into space about 700,000 years ago. It is these dark areas which contain traces of the Martian surface and atmosphere. (image: Andy Tindle)

The meteorite is a type of Martian volcanic rock known as a shergottite and contains abundant glass produced by impact processes on Mars. When this glass formed it trapped not only a sample of the Martian atmosphere, but also traces of soil-like material. The composition of the trapped atmosphere is very close in composition to that detected by the NASA Viking landers in the 1970s and so unambiguously demonstrates that the meteorite is from Mars. The glass also displays relatively high levels of sulphur and fluorine which, together with its distinct trace element signature, indicates that it contains material from the Martian surface.

A further important finding of the study is that Tissint has a similar cosmic ray exposure age to a number of other Martian meteorites, including the important sample EETA79001, collected in Antarctica. It would seem that all these meteorites were ejected into space by a single impact event that took place on Mars around 700,000 years ago.

The research on Tissint undertaken at the Open University involved detailed carbon, nitrogen and oxygen isotope measurements that not only authenticated its Martian origin, but were able to decipher the various atmospheric and soil components it contains.

Professor Monica Grady, head of the Open University’s Physical Sciences Department and one of the scientists who worked on Tissint says: “Tissint is an extremely important sample that has provided us with very fresh material from the surface of Mars that we can study in the laboratory. The recognition of Martian weathering products in Tissint will provide important constraints for the interpretation and evaluation of data currently being collected on Mars by the NASA Curiosity rover.

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