Meteorites unlock secrets of Mars' early atmosphere

Geologists, who analyzed 40 meteorites that fell to Earth from Mars, have managed to unlock secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks.

Their study shows that the atmospheres of Mars and Earth diverged in important ways very early in the 4.6 billion year evolution of our solar system.

Heather Franz, a former University of Maryland research associate who now works on the Curiosity rover science team at the NASA Goddard Space Flight Center, led the study with James Farquhar, co-author and UMD geology professor.

The researchers measured the sulfur composition of 40 Mars meteorites - a much larger number than in previous analyses. Of more than 60,000 meteorites found on Earth, only 69 are believed to be pieces of rocks blasted off the Martian surface.

The meteorites are igneous rocks that formed on Mars, were ejected into space when an asteroid or comet slammed into the red planet, and landed on Earth. The oldest meteorite in the study is about 4.1 billion years old, formed when our solar system was in its infancy. The youngest are between 200 million and 500 million years old.

Studying Martian meteorites of different ages can help scientists investigate the chemical composition of the Martian atmosphere throughout history, and learn whether the planet has ever been hospitable to life. Mars and Earth share the basic elements for life, but conditions on Mars are much less favorable, marked by an arid surface, cold temperatures, radioactive cosmic rays, and ultraviolet radiation from the Sun. Still, some Martian geological features were evidently formed by water - a sign of milder conditions in the past. Scientists are not sure what conditions made it possible for liquid water to exist on the surface, but greenhouse gases released by volcanoes likely played a role.

The study has been published in the journal Nature.