Mars' crust ferries molecules to atmosphere above

Cosmic rays striking the red planet may explain its unexpected xenon and krypton isotope ratios. Amy Middleton reports.

A Curiosity selfie.
NASA / JPL-Caltech / MSSS

Cosmic rays knocking into molecules beneath Mars’ surface create gases that leak into the atmosphere, a new study suggests.

The report, published in Earth and Planetary Science Letters incorporating data from NASA’s Curiosity rover’s “sample analysis on Mars” equipment, nicknamed SAM, suggests the history of Mars is more complex than first thought.

The noble gases xenon and krypton were known to exist in the red planet’s atmosphere thanks to previous studies into the makeup of Martian meteorites.

SAM’s measurements found similar ratios of xenon and krypton isotopes – forms of the elements with extra neutrons in their nucleus – as the meteorites.

But some were a bit off – there was more xenon-124, xenon-126, krypton-80 and krypton-82 than expected.

The researchers suggest cosmic rays smashed into barium and bromine atoms and knocked neutrons from then – and producing the weird xenon and krypton isotope ratios.

A diagram showing chemistry that takes place in surface material on Mars.
NASA / GSFC / JPL-Caltech

"SAM's measurements provide evidence of a really interesting process in which the rock and unconsolidated material at the planet's surface have contributed to the xenon and krypton isotopic composition of the atmosphere in a dynamic way," explains Pamela Conrad from NASA's Goddard Space Flight Centre in Maryland, US.

The relationship between the isotopes in the planet’s crust and atmosphere offer clues about how Mars may have evolved, according to Michael Meyer, lead scientist for the Mars Exploration Program at NASA headquarters in Washington.

"The unique capability to measure in situ the six and nine different isotopes of krypton and xenon allows scientists to delve into the complex interactions between the Martian atmosphere and crust," said Meyer.

"Discovering these interactions through time allows us to gain a greater understanding of planetary evolution."

The new finding may also shine a light on other chemicals trapped in meteorites, as well as adding to our understanding of the process of de-gassing from the surfaces of planets.

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