Analytical chemistry and extra-terrestrial life
detail as commercial mass spectrometers. Since the Viking and Curiosity rovers, many mission concepts that aim to initiate the search for both familiar and agnostic biosignatures on planetary bodies are under development, with the ESA’s ExoMars’ mission objectives being to search for evidence of morphological and chemical biosignatures on the surface of Mars. Another analytical technique that has been used frequently is spectroscopy. Spectroscopy is the field of study that measures and the electromagnetic spectra. The spectra can then be read and used to investigate the composition and structure of matter at many different scales. Infrared spectroscopy is especially suited for planetary research for two reasons. Firstly, planets absorb solar radiation and re- emit most of this energy at infrared wavelengths. This re-emission makes infrared astronomy quite
difficult, as the infrared light is absorbed by the water vapour in the Earth’s atmosphere (Tokunaga, 1983), and therefore infrared telescopes are often higher up on points of relief. But infrared light is also quite useful due to the fact that many important molecules can be detected using their pure rotational spectra. Rotational spectroscopy is the measurement of the energies of transitions between quantized rotational states of molecules in the gas phase. (Bauder, 2011)
Figure 2: The infrared spectra of Methane
Basically, non-polar molecules such as CO 2 do not give any rotational spectres, while polar molecules such as H 2 O, SO 2 and NH 3 all give rotational spectres. This allows astronomers to detect these molecules in the atmospheres of other planets, especially important in the case of H 2 O which is necessary for earth-based life. The gases that are looked for with spectroscopy are mainly oxygen which on Earth is produced by photosynthesis and therefore is a potential bio-signature when using spectroscopy to look at the composition of the atmosphere of other planets. Methane is also produced by life on earth, through microorganisms, so is therefore a gas that is looked for in the atmosphere of other planets. In 2003, using a high-resolution spectrograph at the Infrared Telescope facility in Hawaii and the Gemini South Telescope in Chile, groups of scientists detected methane concentrations of 250 ppb over the planet (Atreya, 2009).These are quite small amounts – Earth has around 1700 ppb – but this could indicate a small amount of microbes which many scientists now believe can be found underground on Mars, where sub-surface ice sheets have been melted due to geothermal heating (Ojha, 2020). Titan, a moon
of Jupiter, has a large amount of methane, with 1.6% of the atmosphere made up of it, which is nearly 1000 times more than the Earth. This amount of methane was
Figure 3: methane clouds on Titan compared to methane clouds on Earth
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