The Curiosity rover landed on Mars in August of 2012, and the robotic explorer has been sending back data characterizing the surface of the Red Planet ever since. Here Freissinet et al. analyze samples collected from four locations in the Gale Crater for organic molecules. All data were obtained from several components of the rover’s Sample Analysis at Mars instrument.
In particular, the team used a combination of two common laboratory techniques: gas chromatography and mass spectrometry, both of which rely on chemically separating components of a sample and analyzing the fragments. Additionally, the rover performed evolved gas analysis, which measures gases released from a heated sample, to strengthen the findings. Because the organic compounds in question occur at extremely low concentrations—less than 300 parts per billion by weight—much of the analysis is devoted to ensuring that the observed signatures are significantly higher than baseline readings within the instrumentation itself.
At a site known as Cumberland drill hole, in the Yellowknife Bay formation, the researchers report the discovery of chlorobenzene (a six-carbon ring with an attached chlorine atom) as well as two-, three-, and four-carbon dichloroalkanes (chains of carbon atoms each with two attached chlorine atoms). The team suggests that the chlorinated hydrocarbons are the product of more complex organic molecules at the Martian surface interacting with natural Martian chlorine over time or during the pyrolysis of the sample. The organic precursors could have arisen naturally on Mars from hydrothermal activity or even biological sources, or they could be exogenous—the product of meteor impacts or interplanetary dust particles that settled on the planet. These measurements represent the first detection on Mars of indigenous organic compounds in surface rocks and addressed a long-standing objective of the Mars exploration program.
The scientists concluded that these chlorinated organic compounds can, in fact, be preserved in the harsh near-surface environment of Mars over geological times. The chemistries associated with their formation give insight into the planet’s history and demonstrate that at the time life appeared on the Earth about 4 billion years ago, the building blocks of life were present in a habitable environment on Mars. Although it’s too soon to give exact dates, the data may eventually help researchers identify when, if ever, organic life may have existed on Mars. (Journal of Geophysical Research: Planets, doi:10.1002/2014JE004737, 2015)
—David Shultz, Freelance Writer
Citation: Shultz, D. (2015), Curiosity rover finds organic molecules on Martian surface, Eos, 96, doi:10.1029/2015EO037083. Published on 12 October 2015.