NASA’s Mars Curiosity rover has measured a tenfold spike in organic chemical methane in the atmosphere around it and detected other organic molecules in a rock-powder sample collected by the robotic laboratory’s drill.
Sushil Atreya, member of Curiosity rover science team, University of Michigan, Ann Arbor:
“This temporary increase in methane — sharply up and then back down — tells us there must be some relatively localized source. There are many possible sources, biological or non-biological, such as interaction of water and rock.”
Researchers used Curiosity’s onboard Sample Analysis at Mars (SAM) laboratory a dozen times over 20 months to sniff methane in the atmosphere. During two of those months, in late 2013 and early 2014, four measurements averaged seven parts per billion. Before and after that, readings averaged only one-tenth of that.
Curiosity also detected different Martian organic chemicals in powder drilled from a rock dubbed Cumberland, the first definitive detection of organics in surface materials of Mars. These Martian organics could either have formed on Mars or been delivered to Mars by meteorites.
Organic molecules, which contain carbon and usually hydrogen, are chemical building blocks of life. Curiosity’s findings from analyzing samples of atmosphere and rock powder do not show whether Mars has ever harbored living microbes, but the findings do shed light on a chemically active modern Mars and on favorable conditions for life on ancient Mars.
John Grotzinger, Curiosity project science at the California Institute of Technology (Caltech) in Pasadena:
“We will keep working on the puzzles these findings present. Can we learn more about the active chemistry causing such fluctuations in the amount of methane in the atmosphere? Can we choose rock targets where identifiable organics have been preserved?”
Researched worked for months to decide whether any of the organic material detected in the Cumberland sample was truly Martian. Curiosity’s SAM lab detected in several samples that some organic carbon compounds were transported from Earth inside the rover. However, extensive testing and analysis yielded confidence in the detection of Martian organics.
Identifying which specific Martian organics are in the rock is complicated by the presence of perchlorate minerals in Martian rocks and soils. When heated inside SAM, the perchlorates alter the structures of the organic compounds, so the identities of the Martian organics in the rock remain uncertain.
Roger Summons, Curiosity participating scientist at the Massachusetts Institute of Technology (MIT) in Cambridge:
“This first confirmation of organic carbon in a rock on Mars holds much promise. Organics are important because they can tell us about the chemical pathways by which they were formed and preserved. In turn, this is informative about Earth-Mars differences and whether or not particular environments represented by Gale Crater sedimentary rocks were more or less favorable for accumulation of organic materials. The challenge now is to find other rocks on Mount Sharp that might have different and more extensive inventories of organic compounds.”
Researchers also reported that Curiosity’s taste of Martian water, bound into lakebed minerals in the Cumberland rock more than three billion years ago, indicates the planet lost much of its water before that lakebed formed and continued to lose large amounts after.
SAM analyzed hydrogen isotopes from water molecules that were locked inside a rock sample for billions of years and freed when the Sample Analysis at Mars laboratory heated it, yielding information about the history of Martian water. The ratio of a heavier hydrogen isotope, deuterium, to the most common hydrogen isotope can give a signature for comparison across different stages of a planet’s history.
Paul Mahaffy, SAM principal investigator of NASA’s Goddard Space Flight Center in Greenbelt, Maryland and lead author of a report published online by the journal Science:
“It’s really interesting that our measurements from Curiosity of gases extracted from ancient rocks can tell us about loss of water from Mars.”
The ratio of deuterium to hydrogen has changed because the lighter hydrogen escapes from the upper atmosphere of Mars much more readily than heavier deuterium. In order to go back in time and see how the deuterium-to-hydrogen ratio in Martian water changed over time, researchers can look at the ratio in water in the current atmosphere and water trapped in rocks at different times in the planet’s history.
Martian meteorites found on Earth also offer some information, but this record has gaps.No known Martian meteorites are even close to the same age as the rock studied on Mars, which formed about 3.9 billion to 4.6 billion years ago, according to Curiosity’s measurements.
The ratio that Curiosity found in the Cumberland sample is about one-half the ratio in water vapor in today’s Martian atmosphere, suggesting much of the planet’s water loss occurred since that rock formed. However, the measured ratio is about three times higher than the ratio in the original water supply of Mars, based on assumption that supply had a similar ratio to that measured in Earth’s oceans. This suggests much of Mars’ original water was lost before the rock formed.
Curiosity is one element of NASA’s ongoing Mars research and preparation for a human mission to Mars in the 2030s. Caltech manages te Jet Propulsion Laboratory in Pasadena, and JPL manages Curiosity rover science investigations for NASA’s Science Mission Directorate in Washington. The SAM investigation is led by Paul Mahaffy at Goddard. Two of SAM’s instruments key in these discoveries are the Quadruple Mass Spectrometer, developed at Goddard, and the Tunable Laser Spectrometer developed at JPL.