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Organic Molecules Discovered, Consistent With Early Life on Mars

Organic compounds called thiophenes are found on Earth in coal, crude oil, and oddly enough, in white truffles, the mushroom beloved by epicureans and wild pigs. Thiophenes were also recently discovered on Mars, and Washington State University astrobiologist Dirk Schulze‑Makuch thinks their presence would be consistent with the presence of early life on Mars.

Schulze‑Makuch and Jacob Heinz with the Technische Universität in Berlin explore some of the possible pathways for thiophenes’ origins on the red planet in a new paper published in the journal Astrobiology. Their work suggests that a biological process, most likely involving bacteria rather than a truffle though, may have played a role in the organic compound’s existence in the Martian soil. Dirk Schulze‑Makuch said:

Thiophene molecules have four carbon atoms and a sulfur atom arranged in a ring, and both carbon and sulfur are bio‑essential elements. Yet Schulze‑Makuch and Heinz could not exclude non‑biological processes leading to the existence of these compounds on Mars.

Meteor impacts provide one possible abiotic explanation. Thiophenes can also be created through thermochemical sulfate reduction, a process that involves a set of compounds being heated to 248°F (120°C) or more.

This self-portrait of NASA's Mars rover Curiosity combines dozens of exposures taken by the rover's Mars Hand Lens Imager (MAHLI) during the 177th Martian day, or sol, of Curiosity's work on Mars (Feb. 3, 2013), plus three exposures taken during Sol 270 (May 10, 2013) to update the appearance of part of the ground beside the rover. (Image: NASA)
This self-portrait of NASA’s Mars rover Curiosity combines dozens of exposures taken by the rover’s Mars Hand Lens Imager (MAHLI) during the 177th Martian day, or sol, of Curiosity’s work on Mars (Feb. 3, 2013), plus three exposures taken during Sol 270 (May 10, 2013) to update the appearance of part of the ground beside the rover. (Image: NASA)

In the biological scenario, bacteria, which may have existed more than 3 billion years ago when Mars was warmer and wetter, could have facilitated a sulfate reduction process that results in thiophenes.

There are also other pathways where the thiophenes themselves are broken down by bacteria. While the Curiosity rover has provided many clues, it uses techniques that break larger molecules up into components, so scientists can only look at the resulting fragments.

Dirk Schulze-Makuch, Technical University Berlin/Washington State University, speaks during the First Landing Site/Exploration Zone Workshop for Human Missions to the Surface of Mars held at the Lunar and Planetary Institute, Wednesday, Oct. 28, 2015, in Houston, Texas. The agency is hosting the workshop to collect proposals for locations on Mars that would be of high scientific research value while also providing natural resources to enable human explorers to land, live and work safely on the Red Planet. (Image: NASA / Bill Ingalls)

Further evidence should come from the next rover, Rosalind Franklin, which is expected to launch in July 2020. It will be carrying a Mars Organic Molecule Analyzer, or MOMA, which uses a less destructive analyzing method that will allow for the collection of larger molecules.

Schulze‑Makuch and Heinz recommend using the data collected by the next rover to look at carbon and sulfur isotopes. Isotopes are variations of the chemical elements that have different numbers of neutrons than the typical form, resulting in differences in mass, adding:

Organisms alter the ratios of heavy and light isotopes in the compounds they produce that are substantially different from the ratios found in their building blocks, which Schulze‑Makuch calls “a telltale signal for life.” Yet even if the next rover returns this isotopic evidence, it may still not be enough to prove definitively that there is, or once was, life on Mars. Schulze‑Makuch said:

Provided by: Washington State University [Note: Materials may be edited for content and length.]

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  • Troy was born and raised in Australia and has always wanted to know why and how things work, which led him to his love for science. He is a professional photographer and enjoys taking pictures of Australia's beautiful landscapes. He is also a professional storm chaser where he currently lives in Hervey Bay, Australia.

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