Scientists working with NASA's Curiosity rover have detected traces of organic carbon on Mars that hypothetically could have been produced by long lost extraterrestrial lifeforms.
The authors stress that they have not been able to determine where the organic carbon came from, but they are also unable to rule out a biological origin.
The work was published in the Proceedings of the National Academy of Sciences (PNAS) journal on June 27.
Mars has long been a target for studies into past life on other worlds. Today it is a cold, barren world with no significant atmosphere, but billions of years ago it was much warmer, had a thicker, more Earth-like atmosphere, and rippled with rivers and ponds providing a potential habitat for microbial life.
However, due to the planet's lack of a significant magnetic field, cosmic winds are thought to have eroded Mars' atmosphere around 3.7 billion years ago and its water soon evaporated.
Organic compounds are found all over the Red Planet. What is different about this new study is the extent to which new samples have been studied, as well as their high concentrations—the amount of organic carbon found is comparable to that found in rocks in some inhospitable places here on Earth.
"In brief, this work is different than other organic detections on Mars because it represents our best efforts to obtain the total amount of organic carbon in the rock, and the source of that carbon," Jennifer Stern, space scientist at NASA's Goddard Space Flight Center and lead author of the new study, told Newsweek.
"Determining total organic carbon abundances in rocks on Mars helps establish a baseline for how much carbon is present as a product of non-biological processes. Should we find a sample that contains much more total organic carbon than other rocks, this would be a very interesting rock to study further for evidence of chemistry beyond geologic and atmospheric processes."
Organic compounds of interest to scientists because it is possible for living organisms to create them, hence the name.
While this may evoke discussion about extraterrestrial life, it's important to remember that depsite their name organic compounds are, at their most basic level, compounds that contain carbon and hydrogen. There are a number of natural, non-biological processes that can make them, such as volcanic activity.
Indeed, scientists believe that a likely explanation as to why Mars is covered in them is that they were created when water reacted with volcanic rock.
"Total organic carbon abundance on Earth is often used as a proxy for biological inputs to a system, but on Mars, we do not see any evidence that life contributed to the carbon found thus far," said Stern—though the study notes a biological origin of the new samples cannot be ruled out.
Stern and her colleagues studied Mars samples from inside 3.5 billion-year-old mudstones collected from a region of Mars known as the Gale Crater. They say their work represents the first quantification of bulk organic carbon in sedimentary rocks on Mars' surface.
The Gale Crater rock samples were chosen because the area is believed to have been formed by what was once a shallow lake environment that might have been hospitable for life. Scientists are looking for clues that this was the case.
To do this, they heated the mudstone samples to 1,500 degrees using what is essentially a powerful oven on board Curiosity, and analyzed the gas that was released—such high temperatures were needed since the chemical bonds in the rock were so strong.
The analysis identified roughly 40 times more organic carbon in the samples than had previously been reported, and also found more organic carbon than had been reported in Martian meteorites.
The authors say it remains to be seen if there is further chemical information in the samples that could pinpoint exactly how they were formed and what processes might have changed them since then.
"Gale Crater Lake appears have been, at least at times, an environment hospitable
to life as we know it, including its emergence," Dimitar Sasselov, Phillips Professor of Astronomy and director of the Harvard Origins of Life Initiative at Harvard University, who was not involved in the study, told Newsweek. "But no evidence yet that it was actually inhabited, or even if it experienced prebiotic chemistry—producing the chemical building blocks for life."
"The identification of organic carbon in the mudstone is one step in the right direction,
but until we have such samples in our labs on Earth, hopefully from Jezero Crater, we can't be sure of the carbon's origins.
"Mars' habitability is like a puzzle—we are slowly adding pieces together, but no big picture yet. The one piece added today is important, because it gives us hope that we are on the right path so far."
Going forward, scientists may take aim at phosphate as a key signature that life once existed on Mars.
"On Earth, phosphate [isotopes] have a strong biological signature, distinct from the igneous basaltic and abiotic background, and Earth has proven a good analog for Mars based on past analyses of phosphate isotope ratios and petrographic analysis of Martian meteorites," Ruth Blake, professor of Earth and planetary sciences at Yale University, who was also not involved, told Newsweek.
"Mars is also rich in phosphorus! So, once sampled and analyzed for isotope ratios, a potentially very clear indication of the presence vs. absence of life should be found in phosphate on Mars."
Uncommon Knowledge
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
