【惑星科学】火星上に有機物はあるのか

Whether chloromethane emissions detected by Mars landers experiments on Martian soil indicate the presence of organic matter on the Martian surface has been a matter of debate, and this question is probed further in Scientific Reports this week. Replication of the Mars lander experiments on a meteorite sample reveal that the chloromethane derives from organic materials in the meteorite. These results indicate that the chloromethane emissions observed on Mars may come from organic material in meteorite debris found on the surface of Mars.

Chloromethane has been detected on two separate Mars missions, but some studies have questioned whether this chemical is a product of thermal reactions of organic material in soil or a terrestrial contaminant. Frank Keppler and colleagues suggest that the former is possible, as a similar process, involving organic matter in the presence of chloride, occurs on Earth. They demonstrate that chloromethane is produced in this way from material in the Murchison meteorite, which fell in Australia in 1969.

Analyses of the chloromethane from the Murchison sample reveal a distinct isotopic signature (a unique chemical ‘fingerprint’) which implies it is formed from organic material of extra-terrestrial origin. Thus, the authors propose that isotope analysis of the chloromethane detected on Mars could determine whether its origin is from organic material that is indigenous to Mars, deposited by meteorites, or contamination from the landers sent from Earth.