Year: 2018-19
Antara Raaghavi Bhattacharya
School: Navy Children School
Grade: 10
City: Mumbai
"Titan is the only moon with a dense atmosphere and the confirmed presence of surface liquid bodies. The liquid bodies of Titan, both surface and subsurface, are composed of liquid hydrocarbons, mainly methane and ethane. These lakes are prime targets for scientific investigations. I believe a mission to Titan to observe two processes – its climatic systems and the possibility of methanogenic life – will revolutionize our understanding of astrobiology.
Titan’s “methane cycle,” similar to Earth’s water cycle, results in lakes, rain, and clouds of methane and ethane on Titan. Its main location and processes are not well understood. Researchers have previously made theoretical predictions about Titan’s weather and climate processes, but there are many gaps in our understanding of Titan’s seasonal phenomena. Cassini orbited Saturn midway through Titan’s southern summer, and noted rainfall in Titan’s southern hemisphere around that period. Dhingra et al. (2019) have very recently confirmed the presence of methane rainfall in Titan's northern hemisphere (i.e. arrival of northern summer), but their observations do not match theoretical predictions. This raises several questions – what causes this difference? How can it be remedied? A mission to Titan will provide answers.
On a related note, another major question being explored is the possibility of carbon-based life existing on Titan. Our entire understanding of life has until now been based mainly on the availability of liquid water. However, it is possible that biochemical pathways using liquid methane as solvent exist (McKay 2005, 2016, Schulze-Makuch 2018). Such hypothetical life-forms could take in hydrogen in place of oxygen, react it with acetylene instead of glucose, producing methane instead of CO2. Acrylonitrile-based structures that could function as cell membranes in such environments have been modelled. Depletion of hydrogen observed in Titan’s lower atmosphere (Strobel 2010) and low levels of surface acetylene (Clark 2010), may be signs of metabolism consistent with the hypothesis of organisms reducing acetylene to methane. The hydrocarbon lakes on Titan might be ideal test-beds to investigate such processes. While measurements of the ratio of concentration of different hydrocarbon species in the atmosphere can provide clues, and have been attempted, the quality of data available from remote-sensing is not conclusive. Atmospheric aerosols perhaps also play a key role. Any verification of such a bio-chemistry would completely change our definition of life and habitable zones, as the presence of organisms in Titan's lakes would mean a second, independent origin of life within the Solar System itself.
Titan is the target that most merits further study. Sending a spacecraft to Titan – with a lander with advanced instruments to analyse the contents of Titan’s liquid bodies, especially near impact craters, and an atmosphere-studying drone – is the only way to get in-situ data to conclusively answer questions raised by these two related processes. A better understanding of Titan’s seasonal phenomena could provide insight into the methane cycle and its effects, and discovering life in liquid hydrocarbons would be compelling evidence that the universe can sustain life forms far more diverse than previously imagined."
