Did NASA’s Curiosity Rover Find Signs of Ancient Life on Mars? An Astrobiologist Explains How We Determine ‘Life’
Lead image by NASA / JPL-Caltech/ MSSS
By Allyson Brady
NASA’s Curiosity rover has identified seven new organic compounds on the planet Mars, according to new research published in Nature Communications.
The researchers believe this organic matter may have been preserved on Mars for more than 3.4 billion years. But is it evidence of life?
It’s not yet possible to determine whether it was delivered by a meteor (or comet or interplanetary dust particles), was formed through geological processes or may be linked to potential ancient life on Mars.
This begs a few questions: What exactly is life? How do we know what to look for? Why is it so hard to determine if an organic compound came from life or not?
As an astrobiologist, my job is to study life in the universe. I have participated in several NASA and Canadian Space Agency (CSA) projects focused on learning how to detect signs of life, as well as training astronauts to be field scientists.
This has taken me to field sites in the Antarctic, hot springs in Western Canada, volcanoes in Hawaii and underwater in British Columbia.
The study of extreme environments on Earth, along with exploration of the lifeless surface of the moon, can help us understand what life can look like. It can also help us understand the other potential non-biological processes that can form organic compounds like ones that have been found on Mars.
Life in extreme environments on Earth
On Earth, scientists study life in extreme environments that we might also expect to find on early Earth or other planets such as Mars. We call these “analogue” environments.
For example, micro-organisms can thrive in the hot springs of Yellowstone National Park, deep underground or in cold icy places like Antarctica.
As astrobiologists, we can use these analogue environments to test equipment and concepts of operation that may be used to plan life-detection missions on other planets. They also help us better understand how life can survive in extreme environments.
Importantly, these environments help us recognize what kinds of evidence life can leave behind. Identifying biosignatures, or unambiguous signs of life, that can be targeted when looking for life elsewhere is critically important.
On Earth, it’s not hard to find evidence of life. Simply look around you. We are also constantly discovering the existence of life in places where it may have once seemed impossible, such as these microbes buried deep in ocean mud.
In fact, finding locations where there is no life is often more challenging.
What is not a sign of life?
The moon does not contain life. Unlike Mars, where there’s mounting evidence of a warmer watery past, as far as we know there’s little evidence to suggest the moon ever had the right conditions to support life.
The moon is a valuable study site for astrobiology because it offers clues about what is not a sign of life. The moon is constantly being hit by objects such as meteorites and asteroids, objects that would have also hit early Earth and Mars, leaving visible craters on the surface.
Meteorites can contain organic molecules such as amino acids and hydrocarbons that look very much like ones we would expect to be left behind by living organisms.
Micro-organisms, just like your own cells, contain lipids, proteins and nucleic acids. When they die, their organic molecules can become trapped in material such as sediments or minerals, and in some cases, preserved over long periods of time. Even if somewhat degraded, they might survive over millions or even billions of years in a recognizable form even if life itself is no longer present.
But life is not the only way organic molecules can form. Some abiotic chemical reactions can produce organic molecules with no life required. These abiotic processes can lead to the formation of simple organic molecules, life’s building blocks, that form the basis of more complex components.
Reports of gases such as methane or the detection of hydrocarbons on Mars could be related to life. However, scientists know that there are other ways these could have formed. As with the compounds discovered by NASA’s Curiosity rover, they may not readily meet the biosignature criteria of being unambiguously biological.
It’s not easy to decide what is a biosignature and what might have an alternative explanation. Studying other locations or materials without life can help.
Analysis of samples brought back to Earth from the asteroid Bennu in 2023 found organics such as sugars, including ribose, for example. Ribose is a component of RNA. This does not mean that there is life on Bennu, instead it shows that these biologically important molecules may be widely distributed in the solar system.
These kinds of investigations tell us that there are some organics that may not make good biosignatures because there is an alternative non-biological explanation.
From the moon to Mars
Exploration of the moon helps create an inventory of organic molecules that, while often associated with life, also have another explanation. They may have been delivered by a meteorite and been preserved all this time.
For example, studies of lunar regolith — the dusty moon version of soil — brought back from the Apollo missions and from recent Chinese-led missions have identified organic molecules such as amino acids, ketones and amines. If these same organics are found on other planets, it means that they are not necessarily signs of life. At least, not on their own.
Prior to NASA’s recent Artemis II mission, astronauts, including Canadian Jeremy Hansen, underwent geology training at sites like the Kamestastin Lake impact structure in Labrador. This training prepared them to make detailed geological observations of the moon.
These geological features might play a role in the preservation of organics, possibly shielding them from high temperatures and destructive radiation, sort of like a fridge. Similar features on Mars may then be good targets for astrobiology investigations.
With a 2028 moon landing planned for NASA’s Artemis IV mission, we will soon have even more lunar material to study. These missions are critical for helping astrobiologists fine-tune those unambiguous signs of life that we can then search for when we get to Mars.
As NASA’s Curiosity and Perseverance rovers continue exploring Mars, and new missions are planned, in the future we may be able to more confidently answer the question of is it life?
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Allyson Brady is an assistant professor in biology at Carleton University.
This article is republished from The Conversation under a Creative Commons licence. All photos provided by The Conversation from various from various sources.
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