Organic molecules known as thiophenes found on Mars are also readily available on Earth in white truffles, mushrooms, coal, crude oil, and wild pigs. Astrobiologists believe that the presence of these organics could signal to their biotic origin and be a sign of ancient life on Mars.
Organic molecules on Mars
Viking landers were the first to detected organic molecules on Mars. Using spectrometry techniques, Viking landers revealed the presence of chloromethane and dichloromethane. These compounds were initially considered to be contamination from the Earth but later realized that it most likely resulted from a reaction of perchlorate with indigenous martian organic compounds. Non-terrestrial organics such as Chlorobenzene were also discovered in Sheepbed Mudstone, Gale Crater on Mars.
Mars has always been considered a potential nominee for extraterrestrial life. Exploring Mars is also relatively easy when compared to other planets in the solar system. Scientists believe that the discovery of organic molecules on Mars (thiophenes) could signal signs of ancient life on Mars as thiophenes also occur on Earth. The only downside to this discovery is that it might be possible that organic molecules on Mars did not have a biological origin rather a chemical one. One hypothesis could be meteorite impacts, which can create these organic compounds through high-temperature chemical interactions.
“We detected several biological pathways for thiophenes that seem more likely than chemical ones, but we still need proof,” said astrobiologist Dirk Schulze-Makuchm, one of the authors. “If you find thiophenes on Earth, then you would think they are biological, but on Mars, of course, the bar to prove that has to be quite a bit higher.”
Thiophenes consist of 4 carbon atoms and 1 sulfur atom arranged in a ring (see image below). Both elements are known to be essential to life. The environment of Mars today is cold and inhospitable but 3 billion years ago Mars was warmer and wetter, which could have given bacteria a chance to facilitate a thermochemical sulfate reduction process” resulting in thiophenes.
Thiophenes on Earth have been found in microfossils and 2.72 Billion-year-old fossil stromatolites, however, it remains unclear if these thiophenic compounds originated internally or from diagenesis of microfossils. Thiophene synthesis during diagenesis as secondary biomarkers is dependent upon 6 factors; thermal maturation, total sulfur and organic carbon content, iron content, clay content, carbonate content, sulfur-reducing bacteria. Apart from thiophene formation during diagenetic processes, a few examples of direct biosynthesis exist e.g. Caldariellaquinone (CQ). CQ is a compound isolated from Caldariella acidophila, which is an extremophile bacteria (that can grow under high temperature and low pH).
Scientists are hopeful to learn more about organic compounds on Mars with Rosalind Franklin rover, which launches in July 2020. The rover will be equipped with Raman Laser Spectrometer and Mars Organic Molecule Analyzer, both of which are able to search and detect organic molecules. Isotope analysis of organic molecules in Martian soil would help in differentiating biotic from abiotic origin. Moreover, laboratory experimentation to explore biotic production of thiophenes under simulated martian environment could help in determining signs of life on Mars.
“As Carl Sagan said “extraordinary claims require extraordinary evidence.“ I think the proof will really require that we actually send people there, and an astronaut looks through a microscope and sees a moving microbe.” Dr. Dirk Schulze‑Makuch said.
Study finds organic molecules discovered by Curiosity Rover consistent with early life on Mars
Sara Zazke | March 5, 2020 | Washington State University, USA.