The Fire on Mars and Kerogen
I was reading through the paper in Science recently, about the discovery of organic matter in Gale Crater on Mars, by the Curiosity Rover (Organic matter preserved in 3-billion-year-old mudstones at Gale crater), Mars, when I came across the following interesting passage:
Immediately preceding the 750°C peak set is a notable O2 release from sulfate decomposition (3), with an increase in CO2 (Fig. 1E) suggesting that combustion limited to the most ignitable volatiles (12) occurred in parallel with pyrolysis. It is also possible that portions of the CO2 and CO (Fig. 2A) were derived from the decarboxylation (2, 3) and decarbonylation of larger organic compounds, which have been observed for Murchison macromolecular isolates (15). The same three peaks are present but less discernable in Confidence Hills data, where the 750°C O2 peak is lower, suggesting that combustion was less influential on hydrocarbon evolution (fig. S1 and S2).
So, we lit a fire on Mars. I don’t recall any of the reports in the media noting this, or if they did, it was downplayed. A bit of burying the lede, in my opinion. After all, one of the first things human beings do, and probably always did, in any new land that they explore, is to start a fire. So, this “Martian fire” strikes me as quite symbolic. Sure, it was a fire confined to a glorified test tube, but still…
As the graph shows, there was a fairly sudden release of oxygen from the pyrolysis of the sample (i.e. heating of the instrument, via energy from a radioactive source on the probe), once the temperature reached about 700 C. That was followed by CO2, which peaked a bit later in the experimental run. So, it looks like a short, small blaze might have occurred. At any rate, a fairly rapid oxidation.
The idea behind the experiment was to sample a 3 billion year old Martian mudstone, located in the Gale Crater, then heat it up and test the resulting by-products, with a particular focus on whether and how much of the compounds detected were organic, in the sense of organic chemistry (i.e. carbon based molecules).
There was some precedent for believing that there would be organics – hints of this came from earlier work by Curiosity, as well as Martian meteorites that had fallen on Earth.
At any rate, quite a rich soup of organic molecules were detected by the mass spectrometer. Again, quoting the paper (note that the reference to Mojave and Confidence Hills are sites on Mars):
The diversity, composition, and temperatures of coevolving volatiles observed in the Mojave and Confidence Hills analyses above 500°C are consistent with the pyrolysis of geologically refractory organic macromolecules that are typically found in carbonaceous chondrites (14, 15), kerogens (17), and coals (18, 19).
Note that kerogen is a general term for a mixture of solid organics in sedimentary rocks on Earth (it is a coined word that translates from Greek as “wax birth”). On Earth, kerogen is thought to be a by-product of living things, and can eventually turn into petroleum, natural gas or coal.
That said, it is known that kerogen-like matter can come from non-living sources (e.g. it can be found in interstellar clouds and carbonaceous chondrite meteorites). We obviously don’t know the source of the Martian material. The paper notes that biological, geological or meteoritic sources are all possible.
The Connection to the Viking Experiments
The Viking lander experiments of the 1970’s showed tantalizing indications of life, in the Labelled Release results. These tests “fed” a rich nutrient mixture to some Martian soil, and then looked for radioactive traced CO2 gas, that would be released by life forms in the soil, if they were metabolizing the nutrient mixture. The experiments did show such a result, and they were consistent with results tested on Earth soils in which bacteria could be found. However, the life explanation was mostly abandoned in favor of non-biological chemistry.
One of the main refutations of the “it’s life” interpretation of the Labelled Release experiment was that another Viking experiment that was designed to look for organic matter, failed to find any. However as a 2016 paper by two of the Viking scientists states:
“Lack of biologically relevant organic molecules on the surface of Mars has also been considered a major detriment to extant life. Recent reports of complex organics, possibly of biological importance, are encouraging, although analyses are ongoing and details are not yet available.”
The 2018 results from Curiosity certainly should bolster the case for Viking’s apparent discovery of life in the Labelled Release experiment.
The Connection to Science Fiction
An interesting connection to Science Fiction comes from an old 1960’s movie called “Robinson Crusoe on Mars”. In that movie, a stranded astronaut derives oxygen from heating oxygen-bearing rocks. So, it is interesting that there is a bit to this idea, as far as we can tell from the Curiosity results. Here’s a scene of the stranded astronaut filling his oxygen bottles (and, yes, he has a monkey).
The movie was filmed before much was known about Mars, even before the first NASA spacecraft did a flyby of the planet. The movie was from 1964, and the first Mars probe flyby was in 1965. It is a surprisingly good movie, for the most part, though the last part is a stretch. It is well worth a viewing.
- Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars. Buch and Patrice Coll, Joel A. Hurowitz, John P. Grotzinger, Sanjeev Gupta, Doug W. Ming, Dawn Y. Sumner, Cyril Szopa, Charles Malespin, Arnaud, Brad Sutter, Amy C. McAdam, Heather B. Franz, Daniel P. Glavin, Paul D. Archer Jr., Paul R. Mahaffy, Pamela G. Conrad, Jennifer L. Eigenbrode, Roger E. Summons, Andrew Steele, Caroline Freissinet, Maëva Millan, Rafael Navarro-González DOI: 10.1126/science.aas9185 Science 360 (6393), 1096-1101.
- The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment. Gilber V. Levin and Patricia Ann Straat
- Wikipedia (Kerogen, Mariner 4 Mars Probe, Robinson Crusoe on Mars, Viking Probe)
- Google Images
And now that you have read about some real cutting-edge science, you should think about reading some Science Fiction (because all work and no play can make you a dull person, or so they say). Here’s a novel that features a neutron star (and a pretty girl, who is also an engineer, among other characters). The second book in the series features a lunar near-catastrophe and some science about Lagrange points:
The Witches' Stones, Book 1 - Rescue from the Planet of the Amartos
Young Earth woman and spaceship mechanic, Sarah Mackenzie, has unwittingly triggered a vast source of energy, the Witches' Stones, via her psychic abilities, of which she was unaware. She becomes the focal point of a desperate contest between the authoritarian galactic power, known as The Organization, and the democratic Earth-based galactic power, known as The Terran Confederation. The Organization wants to capture her, and utilize her powers to create a super-weapon; the Terra Confederation wants to prevent that at all costs. The mysterious psychic aliens, the Witches of Kordea also become involved, as they see her as a possible threat, or a possible ally, for the safety of their own world.
A small but fast scout-ship, with its pilot and an agent of the Terra Confederation, Coryn Leigh, are sent to rescue her from a distant planet at the very edge of the galaxy, near space claimed by The Organization. Battles, physical and mental, whirl around the young woman, as the agent and pilot strive at all costs to keep her from the clutches of the Organization.