Using assembly theory in conjunction with fragmentation tandem mass spectroscopy, scientists are suspected to have found the first experimentally verifiable methodology for detecting evidence of alien life.
Differing from complexity algorithms and other methods that lack experimental measure, astronomical probes fit with mass spectroscopy may be used to gather concrete evidence of extraterrestrial life. Apparatus such as the SuperCam, the pyrolysis-gas chromatography-mass spectrometer (Pyrolysis-GC-MS), and the laser-based mass spectrometer encompass just how far we have come in the field of extraterrestrial exploration.
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Requirements for life
For life to occur, according to our currently known parameters, three essential components are needed: nutrients, energy, and water. This is our only known template; we have no other means of knowing what life would look like otherwise. The following will use mars as an illustration.
Various organic molecules such as benzene, thiophenes, and toluene have been found on Mars’s surface. Organic minerals can be used to essentially keep an organism running, and while this criterion has been met, others fall short. Though Earth itself is closer to the sun than Mars, the photon energy Mars receives is more abundant.
The answer lies within the higher ionizing radiation levels, which lie between 10-100x times stronger than those on earth- on account of atmospheric composition. This radiation would be damaging to any life form that we can conjure.
The final prerequisite for life is water, something that is not readily available on Mars. Through mass spectroscopy fit to the perseverance rover we have discovered dried river systems, denoting a substantial amount of past liquid surface water.
For all these reasons, Mars cannot be considered a viable candidate for eukaryotic, complex life forms. This has led NASA, and other space exploration companies, to try a new front- exploring subsurface microbial life, or life that has long gone extinct. These species would only be micrometers in size, and very difficult to detect
When the Mars 2020 Perseverance landed, a bygone stream known as the river delta was surveyed on the surface of Mars. Though this stream has been depleted for some time now, merit still lies in its analysis. It is speculated that there may be sufficient residual moisture that descended to the subsurface- this water could have the potential to host microbes. In addition, the life that could have once resided in this arroyo might still be there in fossilized form. Biomarkers could have been left as evidence of past life.
How the SuperCam’s laser induced spectroscopy is used to detect life
Biomolecules, and biogenic elemental isotope ratios are the first targets that exploratory probes survey. These can be preserved in rock, soil, icy material, etcetera. Some of the instruments that fit the exploratory crafts are the SuperCam (using mass spectroscopy), and the Pyrolysis-GC-MS.
The SuperCam fit to the Mars 2020 Perseverance Rover performs laser-induced breakdown to perform spectroscopy. This technique incorporates remote sensing, where spectroscopy can be performed on analytes that are 2-3 meters away.
This process incorporates a high-powered laser which is used to atomize a specimen using high energy to excite. Once these atoms are highly excited, they try to migrate to their ground state, emitting light. By forming a spectral graph to capture the light, the composition of said species can be determined. These methods can work on both non-living, and biological entities.
Though the boons of this device are plentiful, some drawbacks can clearly be denoted. The objective of this device is to detect small biological signatures; however, the spatial accuracy of its instrumentation is less than ideal.
The SuperCam uses a laser that is 100 μm thick. This means that analysis of the chemical makeup of microorganisms (typically 1-2 μm thick), is obstructed by surrounding material and non-analytes. This spectroscopic technique is also inherently low in sensitivity because only a fraction of light emitted from the sample (due to plasma), is captured by the rover.
Light is emitted at 360 degrees, and because the rover does not wholly capture all angles of light diffraction, it will significantly dilute the signal.
The two readings that are taken into consideration when exploring Martian life are visual signatures and chemical indicators. Mineralogical records of life could be an example of a visual signature. An example of a mineralogical record on earth would be coral reefs, providing clear evidence that biological activity took place. We have not yet found an analog on Mars though explorations are underway. Chemical indicators come next, which include specific isotope ratios and preserved waste. These can indicate past lifeforms.
How pyrolysis-gas chromatography-mass spectrometer (Pyrolysis-GC-MS) is used to detect life
Though this instrument was omitted from the Mars Perseverance Rover, other rovers like the Viking 1 and Viking 2 are fit with Pyrolysis-GC-MS. Holding an extensive resume within the field of planetary science, Pyrolysis-GC-MS will analyze molecules in a gas medium. Essentially this machine will take soil samples and heat them to 200-400 degrees Celsius, while a flame ionization detector (FID) or ion trap supposedly detects the signature of a biomolecule. Though this has proven somewhat effective, there are many drawbacks to this device. We might have already encountered a smattering of different biosignatures using Pyrolysis-GC-MC, however, the impediments this device holds will cause the telling of a different story.
Many biomolecules such as certain amino acids have a melting point that is below 200, while DNA and RNA will decompose at higher temperatures, rendering this technique obsolete. Not only this, but the surface of Mars contains many perchlorates and other corrosive salts. When this is placed into the Pyrolysis-GC-MS oven, reactive compounds such as strong acids like oxygen radicals and hydrogen chloride will form.
When these gases come into contact with organic matter, a combustion reaction will form to generate CO2 and water, effectively destroying it.
To bypass these issues of chemical alteration, novel instrumentation has been implemented with high sensitivity and excellent spatial resolution, all while preserving biotic samples. Devices such as the laser-based mass spectrometer cover laser resorption and laser ablation ionization mass spectrometry, exhibiting our potential for planetary assays.
Sources:
- T.P. Wampler (2014), Pyrolysis-Gas Chromatography. Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, Elsevier ISBN 9780124095472
- McKay C. P. (2014). Requirements and limits for life in the context of exoplanets. Proceedings of the National Academy of Sciences of the United States of America, 111(35), 12628–12633.
- Chancellor, J. C., Scott, G. B., & Sutton, J. P. (2014). Space Radiation: The Number One Risk to Astronaut Health beyond Low Earth Orbit. Life (Basel, Switzerland), 4(3), 491–510.
- Pla-García, J., Rafkin, S., Martinez, G. M., Vicente-Retortillo, Á., Newman, C. E., Savijärvi, H., de la Torre, M., Rodriguez-Manfredi, J. A., Gómez, F., Molina, A., Viúdez-Moreiras, D., & Harri, A. M. (2020). Meteorological Predictions for Mars 2020 Perseverance Rover Landing Site at Jezero Crater. Space science reviews, 216, 148.
- National Research Council (US) Committee on the Origins and Evolution of Life. Signs of Life (2002) A Report Based on the April 2000 Workshop on Life Detection Techniques. Washington (DC): National Academies Press (US); 1, Detection of Life.
- Biemann K. (2007). On the ability of the Viking gas chromatograph-mass spectrometer to detect organic matter. Proceedings of the National Academy of Sciences of the United States of America, 104(25), 10310–10313.
Further Reading