What meteorites reveal about Mars

Unlike the Moon, there are no soil samples from Mars that space missions have collected and brought back to Earth. This makes exploring Mars geologically more difficult. In addition to Martian rovers analyzing rocks in situ, there is another possibility: Martian meteorites. A research group has now examined several of these meteorites. In the journal Science Advances they report on the internal structure of Mars and the differences from Earth.

About 11 million years ago, a large meteorite struck Mars. Fragments of the Red Planet were thrown into space and over time fell to Earth in the form of meteorites. The first were discovered by researchers in Chassigny, France, in 1815 and in Nakhla, Egypt, in 1905. Two types of Martian meteorite rocks are named after these two sites: chassenite and nakhalite. Chassenite consists almost entirely of olivine; Nachlite contains basalt – similar to lava from volcanic eruptions in Iceland or Hawaii.

We know that this rock comes from Mars for three reasons: First, the meteorites are young and therefore come from a planet where a new rock recently formed – which means they were only recently volcanically active. Secondly, their composition is different from terrestrial rocks. Third, part of the Martian atmosphere is trapped in rocks, and its composition is consistent with measurements of the Martian atmosphere made by Viking probes in the 1970s.

James Day of the Scripps Institution of Oceanography at the University of California, San Diego, and his team examined both nakhlite and chassenite using different chemical analysis methods to determine their components. They found that nakhliite and chassenite come from the same volcanic system. From a uniform mixture of magma, different types of rocks can arise through what is called fractional crystallization: different minerals crystallize in the liquid magma at different times and settle one after the other. This created a Martian crust with different layers. Chemical analysis also showed that some of the palm trees contain parts of the Martian crust near the surface that interacted with the Martian atmosphere.

Similarities and differences with Earth

What particularly catches Day's attention is that volcanic activity on Mars is very similar to volcanic activity on Earth in some ways, but significantly different in others. This is how nachliite and chassenite formed under conditions similar to those prevailing in volcanic regions on Earth: newly formed volcanoes press on the planet's mantle and thus generate tectonic forces from which more volcanoes then arise. However, the magma reservoirs on Mars are very old compared to Earth. On our home planet, individual reservoirs are constantly mixing due to tectonic plates – but this may have been different in the past and Earth would have been more like Mars in this respect.

Laboratory studies of Martian rocks are of great value for research: in laboratories on Earth, Martian soil samples can be analyzed better and more accurately than in situ Mars rovers. For this reason, NASA and the European Space Agency, among others, are planning a “Mars Sample Return” program, where they want to bring soil samples from Mars to Earth. Subsequent investigations will likely be able to provide more information about the geology of Mars.