Earth-Based and Spacecraft observations of methane on Mars
Introduction
NASA Curiosity Rover has been active on the Martian surface since 2012 and was responsible for detecting spikes in methane around Gale Crater during its ascent of the Mount Sharp summit. Mars, a terrestrial (rocky) planet, has had a history of very low methane content in its atmosphere. However, over a period of 605 sols (Mars days), Curiosity (the NASA rover) recorded traces of methane gas by collecting air samples and separating the Carbon dioxide (CO2) from other constituents to derive pure methane (CH4), through a process called spectroscopy. Spectroscopy is passing visible light through gases so as to produce a specific spectral pattern used to identify the gas. After announcing this discovery at the Geophysical Union in San Francisco, it was found that methane is rare occurrence on terrestrial planets and rather is mostly found in gas giants like Jupiter, having formed billions of years ago. Seasonal changes in methane are very unique by researcher’s estimates. Methane is also often considered a reliable signal of life for its possible biological origins. Some of the areas of interest for methane samples include Nili Fosssae (hydrated mineral source) and Syrtis Major (substrates).
Air Samples
Mars contains 95.32% CO2 in its atmosphere with traces of other gases (O2 is just 0.13% and N2 is just 2.7%). With the absence of tectonic convection (layers of crust and mantle sliding over one another), MAVEN NASA probe has shown that the lack of friction prevented a magnetic field from shrouding Mars and this allowed the strong solar winds and cosmic rays to tear away whatever little atmosphere remained. With a short life-span for methane and without a continuous methane-cycle replenishing the CH4 like how it is done on Earth, the methane gas plumes detected could be assumed to be relatively recent. Instead of being sparsely dispersed, they are concentrated at certain crater/valleys and move faster than the rover does, hence making it difficult to record data. This suggests the simple idea: Mars is alive, either geologically or biologically.
Body
Parallels with Earth
In comparison to Mars’ tiny 0.4 ppbv (parts per billion volume), Earth has an overwhelming 1800 ppbv via a functioning methane cycle that replenishes the short-lived methane gas. Most common sources include rice stocks, termites, landfills and other biogas dumps, and ocean microbes. In these sources, anaerobic bacteria produce this methane through respiration without oxygen, producing methane rather than CO2. Biggest source, however, are the burning of fossil fuels. Most of these “natural processes are not possible on Mars which is what makes the gas’ presence so intriguing.
Sources on Mars
Methane was first discovered on Mars through ESA’s (European Space Agency) Mars Express. Ironically, most of the places on Mars where methane has been detected have had a history of presence of water in the past, possibly hinting to the biological origins of the gas so linked to life processes. Most researcher agree on the three-part hypothesis as possible sources of Methane. They are:
Biological Life
Chemical or Geological Occurrence
Random Outburst (meteor/comets/other unpredictable phenomenon)
The presence of microbes called “methanogens” on Mars could be a potential source for the gas through biological processes like those on Earth called, aptly in this case, “methanogenesis”. This theory is currently the most widely researched one among the three as it is exciting for scientists to discover the possibility of life.
In the past, there was an abundance of surface organics rich in Carbon (C). These, however, were broken down by UV (Ultra Violet) rays from the Sun and cosmic rays. Methane has the tendency to change into formaldehyde and methanol to eventually produce CO2, which could explain the 95% dominance today. There is still a lot of carbon and more is being produced daily, but the rate of CO2 production is slower.
Hydrothermal reactions with rocks like Olvine (igneous rocks) or pyroxene are chemical sources and sinks for methane. Through a process called serpentinisation, rocks rich in ferromagnesian (iron-magnesium) minerals react in low-temperature water to produce new types of rocks and release hydrogen as the end product. This hydrogen then reacts with carbon monoxide to eventually produce methane. Some of the CH4 gas produced can be stored as ice-crystals, acting as cages or aquifers sinks, called clathrate hydrates. The seasonal heat on Mars melts these crystals causing the methane gas to be produced in a sudden burst from underground gaps/zones.
Perchlorate deliquescence is another source where rocks containing perchlorate salts, found near Curiosity research sites, collect methane as dry salts which react with water (which acts as a catalyst), and expel methane gas. This occurs usually during high humidity periods in Martian winter.
Random outbursts like compressed CO2 gas combining with water under high temperatures and pressures, along with dust being spread by carbon-rich meteorites falling to the surface of Mars annually, could be also considered as possible sources of methane.
Seasonal Spikes
The release of methane happens in a cyclical method on mars, described as almost seasonal. Life on Earth is seasonal, and this only strengthens the hypothesis that the methane comes from biological sources. However, in addition to sources discussed earlier, the sources for CH4 could be more localized.
Dust Devils (strong, sustained whirlwinds averaging 60 mph) on the surface produce static electric fields that acts as a sanitizing agent in the form of Hydrogen Peroxide (H2O2). This breaks down organic minerals and produces methane gas.
In the case of comets and meteors, scientists suggest the interplanetary rocks would have to be several meters across to bring in sufficient amounts of carbon and hence upon impact should leave noticeable craters. However, the abundance of craters was unfound. In addition, there is a sheer lack of evidence for volcanic activity in being a possible source for the methane due to absence of tectonic convection.
According to discoveries through Curiosity’s Tunable Laser Spectrometer (TAS/TLS), intense light was used to carry out chemical analysis test to produce spectrums and identify elements. A lack of methane was recorded over a period of two months. Surprisingly, soon Curiosity showed a spike of methane from a mere 0.7 ppbv (parts per billion volume) to 7 ppbv, a staggering ten-times (1000%) increase. Most of the spikes that occurred were about 200-300 meters from each other and within a kilometer radius of other generally low readings.
In Mars’ past, there was the possibility of abundant water which could have sustained life because the current concentration of CO2 cannot explain the continual warming of the planet since its long ago “ice-age” where polar caps dominated much of the northern hemisphere. Only a greenhouse gas like methane which has a history of trapping extreme heat could be the hypothetical perpetrator for the noted rises in temperature.
SAM and TLS
The Sample Analysis at Mars (SAM), operated by NASA has three parts to it: spectrometer to measure mass, chromatograph to identify and segregate gases, and TLS (Tunable laser spectrometer). Although it also records minor changes in other life-related gases like Nitrogen (N2) and Oxygen (O2), the TLS mainly records changes in methane for sites with maintained temperature and pressure zones. The instrument absorbs some of the untouched Martian air into a cup-shaped container the size of a coffee mug. Firing an Infrared (IR) beam through the gas to see how much of it is absorbed. This produces an absorption spectra and scans the different uniquely identifying patterns to detect traces of methane. The TLS is very precise and conducts experiments on oxygen and chemical isotopes in carbon-rich gases to judge the gases’ origins.
The TLS is extremely sensitive and can detect methane and water vapor to single-digit ppbv quantities. To further improve the sensitivity, the air is consumed slowly by SAM and passed through a rough CO2 filter to extract the carbon dioxide and separately collect methane gas, making it unmistakably detectable. In the past, the TLS has been used here on Earth to measure chlorine deposits in the ozone layer, and methane composition in different locations, and it was this proven effectiveness that helped inspire NASA scientists to use the same technology for Mars.
MAVEN
The Mars Atmosphere and Volatile Evolution mission (MAVEN) entered Mars orbit in 2014 and since then has been assigned to study the magnesium ions in the planetary atmosphere in relation to its interactions with solar winds. It has found that a lot of gases, like CO2, H2 and N2, have escaped from the exosphere into outer space and using this information, MAVEN hopes to reveal Mars’ potential biological past.
Results from MAVEN have shown that once upon a time, Mars used to have a thriving atmosphere which stored CO2 and helped in sustained warming of the planet. However, coming back to present day, we can see that the lack of atmosphere meant the sun’s warmth couldn’t be retained on the surface and hence cause Mars to become dry, dead, and fossilized today. Reasons for this can also include kinetic motion of excited ions pushing other ions out of the atmosphere, UV rays breaking down gases like CO2 and methane.
Curiosity Error
There have been a lot of debates questioning the legitimacy of the sources of methane detected on Mars. Some researchers believe that the supposedly “microbial methane” was actually from earth microbes that the rover got contaminated by when it launched. The microbes having survived the space journey, are currently making the gas detected gas. There could be some trapped methane in the SAM and TLS antechamber from Florida (launch site) which could fudge the results and hence give wrong indications.
According to NASA, when the SAM was first switched on, there was a sudden spike in methane readings, and they concluded that this air was that of Earth, and dismissed these skewed readings.
Nevertheless, Curiosity, as a mission, was never designed to search for microbial life through imaging, sampling fossils and experimenting generic metabolic reactions to study life and hence a recommendation from me would be that NASA should send a specific mission target on biological analysis, or perhaps conduct a collaborate private-public mission to Mars.
Conclusion
ExoMars TGO
European Space Agency (ESA) launched the Trace Gas Orbiter (TGO) in 2016 with the sole purpose of collecting methane and other trace gas samples as a possible arrow towards presence of life on Mars and could be considered to set the precedence for future missions through ESA. A massive new drill, advance equipment and demonstrator modules like the Schiaparelli EDM (for entry into atmosphere and landing on Martian surface), will help tackle inconclusive reading of methane releases to greater accuracy at targeted/specific Martian hotspots. It hopes to better understand Mars, its history and the potential for microbial life on the red planet.
SpaceX and methane
SpaceX, for its future missions, plans to use Martian methane, in an engine called Raptor, as a propellant for its rockets to minimize costs, store efficiently. Instead of carrying return fuel to mars and having extra weight (which in-turn leads to greater fuel consumption and creates a vicious cycle), this is better. Using an abundant ice reserves in the polar caps and CO2 in the air, Elon Musk hopes to generate the methane-fuel using solar energy. Although work is yet to begin on these propellant manufacturing stations, it might just be possible.
Mars 2020
Mars has planned to launch a new biologically-focused mission to Mars by 2020. This rover will carry seven new instruments including a radar system to detect underground ice and water deposits along with a laser that detects carbon atoms specifically. There will be a staggering 23 cameras with lasers to vaporize rocks and extract minerals from them. It will also have a rock storage system for future analysis with improved drilling equipment, efficiency in power usage, coupled with advanced spectrometers. In summary, the Mars 2020 project is designed to find evidence for microbial life, research the habitability, and help eventually advance the possibility of human settlement on the red planet.
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