Oil Discovered On Mars
I recently wrote a post on Facebook about a discovery recently announced by NASA and JPL. The Mars Curiosity rover drilled a hole in a mudstone in Gale Crater and analyzed the sample with its chemical instruments. The analysis showed trace amounts of C10, C11 and C12 hydrogen-saturated carbon chains. Oil. Black Gold. Texas Tea.
Cumberland mudstone drill-site. I should write headlines for supermarket tabloids.
The Curiosity Rover is exploring a former lakeshore in Gale Crater, located near the Martian equator. The crater formed between 3.8 and 3.5 billion years ago, and was periodically filled with water from the time of its formation until about 2 billion years ago. Scientists studying the spectra of minerals from Mars orbit identified the crater as a likely location to find shoreline deposits and evidence of former life.
After I posted my note, a Facebook friend immediately asked the most important question, “For real? Doesn’t that mean there was life?” I gave a waffling answer which probably left Tom unsatisfied. Certainly, on Earth, oil is the product of thermal alteration of biological materials, primarily algae, leading to the formation of crude oil. But there are non-biological processes in some hydrothermal environments that can lead to the formation of these molecules.
Curiosity drilled this sample in 2013, and the immediate results showed small carbon molecules. The rover stored portions of the sample for later analysis. Since then, NASA/JPL conducted experiments trying to replicate the origin and detection of these molecules. NASA scientists developed a new procedure to test for larger carbon molecules, and reconfigured the equipment on the rover to test the stored sample. (A third sample exists on the rover for future testing.) The recent test with reconfigured equipment showed the presence of the large carbon molecules. NASA/JPL now think that the large carbon molecules were produced from fatty acids in the original sample, which were altered to carbon chains during heating for the chemical analysis. It is possible to produce fatty acids in hydrothermal environments in earth environments, so the finding is not yet diagnostic of life.
To be clear, the concentration of the long-chain carbon molecules is very small; on the order of one part to ten parts in 100 billion. (The concentration given in the press release is given as tens of pico-moles.) But this is within the sensitivity of the rover’s instrumentation.
It’s hard to generate carbon chains from water and carbon dioxide using non-biologic processes. Long carbon chains are even more difficult. That’s why large and complex carbon molecules are considered diagnostic of life, termed biosignatures. Lipids, carbohydrates, nucleic acids and proteins are considered biosignatures, among others. These would be considered proof of former life.
Intriguingly, the detection of C12 is at the upper limit of the capability of the instrumentation on Curiosity. It’s possible that longer chains existed in the sample. Also, JPL scientists note that non-biological processes usually produce shorter fatty acids than 12 carbon atoms, but that the C12 molecule detected in the Martian sample was more abundant than C10 or C11.
Proof
We use different standards of proof depending on what we are trying to prove and why. In civil cases, we use the standard of preponderance of evidence; more than 50% of evidence is considered sufficient proof. In criminal cases, we require a higher standard, termed reasonable certainty. Reasonable certainty is not well defined, but is generally understood and used by juries. In science, the standard of proof is usually held to be an unequivocal finding, meaning that all evidence-based alternatives have been examined and refuted. Mathematical proof is a higher standard, with a demonstration that it is not possible for the assertion to be false.
For the Mars samples, I would say that the preponderance of evidence is that Curiosity has discovered chemical proof of extraterrestrial life. The sample was taken on an ancient lakeshore, which is a likely place for algal growth. There is little evidence of local hydrothermal activity, which would be the only alternative explanation for the occurrence of long-carbon chain molecules. (Although the rover has discovered elemental sulfur nearby, of unknown origin.) Other chemicals found nearby are consistent with life, including chlorinated and sulfur-containing carbon compounds, carbon-ring compounds (aromatics) including benzoic acid, nitrates and elemental sulfur. The relative abundance of C12 also points towards a biologic origin for the molecules.
But the finding is slightly less than reasonable certainty, and is not yet unequivocal. Additional sampling and testing are needed to prove the existence of more complex carbon molecules, or to disprove the possibility of non-biologic generation of long-chain carbon molecules.
Astronomer Carl Sagan was preoccupied with the planet Mars and alien life from a young age, something that led to his stunning career. Sagan also coined the aphorism, “Extraordinary claims require extraordinary evidence.” So, what is an extraordinary claim? An extraordinary claim may be: 1) something that violates known scientific knowledge or processes, 2) something that is within the realm of scientific possibility, but with an extremely low likelihood of occurrence, or 3) something that is outside the envelope of prior experience. The possibility of ancient life on Mars is in the third category of extraordinary claim. This would be the first discovery of extraterrestrial life, and therefore requires extraordinary evidence, stronger than what has been discovered to date by Curiosity’s instruments.
In the official press release announcing the discovery of large carbon chain molecules, NASA described the molecules as “pre-biotic”. I think that ultimately, further research will prove the existence of ancient primitive life on Mars. Given the evidence, I would be surprised if the discovered chemistry is not the result of self-replicating processes sufficient to be considered life. It’s a thought worthy of contemplation, that primitive life may have lived on Mars simultaneously with cyanobacteria or algae on earth. But on Mars, through planetary bad luck, the atmosphere and oceans were stripped away by the solar wind, while Earth was protected by its magnetic field. And so, we, the descendants of cyanobacteria on Earth, are sending interplanetary probes to Mars, instead of the other way around.
Image of a city on Edgar Rice Burrough's Barsoom (Mars). Image credit Woodrow Edgar Nichols, Jr.
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Afterword
NASA’s Opportunity rover landed on Mars in 2004. At the time, I was working as an international exploration petroleum geologist for a major oil company. I had previously studied images of Mars taken from NASA orbiters, and noted clear signs of water channels, and I was quite interested in the new mission. Opportunity landed in Eagle crater, and its first photos showed an outcrop of a likely fluvial sandstone. I was gob-smacked. I printed a photo and taped it to my office door, without explanation. The Vice-President of exploration wandered down the hallway, and curious, asked me where the photo was from. I told him it was Mars. We agreed that the photo looked like sandstone, and I joked that maybe someday we would find oil on Mars. He didn't seem amused. But twenty years later, here we are.
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