Mars building blocks for life, NASA’s flagship Mars rover, Curiosity, has been combing the surface of Mars for signs of life for almost six years. These hints of habitability, called biosignatures, can come in many forms—from unique sediment deposits to the abundance of certain gases in the thin Martian atmosphere.

One possible biosignature on Mars—or a sign leading to potential biosigantures—is the presence of organic compounds. Almost all molecules containing carbon are organic compounds, and these molecular structures are frequently produced and consumed by living organisms. There are other ways to produce organic compounds, so they are not a smoking gun for life—but they are an awfully good sign.

And Curiosity just found an abundance of organic compounds on Mars.

Two studies (1, 2) published today in the journal Science solve past mysteries surrounding organic compounds on Mars. The first study found several new organic compounds in samples of ancient Martian mudstone that is roughly three billion years old, while the second charted seasonal fluctuations of one of the most basic organic compounds: methane.

The mudstone samples analyzed by Curiosity came from Confidence Hill and Mojave, two sites near the base of Mount Sharp in Gale crater. Curiosity drilled samples of mudstone in a region that is thought to have been a lake about three and a half billion years ago. The rover heated the Martian soil to above 500 degrees Celsius and analyzed the compounds released in the gases with its Sample Analysis at Mars (SAM) instrument. Numerous organic compounds were discovered, including thiophene, 2- and 3-methylthiophenes, methanethiol, and dimethylsulfide.

The researchers, led by NASA biogeochemist and geologist Jennifer Eigenbrode, note that because the organic molecules differ by just one carbon sidechain, they may be fragments of larger and more complex molecules. Eigenbrode says that fact strengthens the evidence that the region in Gale crater could have been habitable in the distant past.

“The organic matter in the ~3.5 billion-year-old lake sediments could be from life, but it is not evidence of life since non-life processes could have also created organic matter that ended up in these rocks. Meteorites and geological processes can form organic molecules and are additional possible sources for the organic matter we found. [But] even if life was not present in the ancient lake, the organics could have been food for life and thus are considered another ingredient for supporting life. The finding reinforces the idea that the ancient lake was habitable, but we don’t know if it hosted life.”
Additionally, Curiosity has been conducting in-situ measurements of methane in the atmosphere for three Martian years, or 55 Earth months. Previous trace amounts of methane have been detected on Mars, but the source of the gas—which is produced in abundance by life on Earth—remained a mystery.

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