The recent discovery of a life-signature chemical far out in space has created great interest in the scientific community and news media alike and resonates for GCSE and A- Level students not just of Chemistry but Physics and Biology too.
A signature chemical detected on a far-away planet
Cambridge University astronomers have detected the presence of a compound dimethyl sulphide (DMS) in the atmosphere of an exoplanet called K2-18 b. It is situated 124 Light Years away from earth (meaning it would take light travelling at 300 million meters per second about a hundred and twenty four years to travel the 700 trillion miles to reach it – so don’t plan a holiday there!)
The planet is 2.6 times the radius of earth, but because it is fairly close to the star that it orbits (a Red Dwarf), it only takes 33 days to complete the orbit, meaning its Year is only 33 days as opposed to our 365 days.
But why is this biosignature of DMS (CH3SCH3) so interesting? It is because we have this compound in our earth’s atmosphere too and it is produced by the billions of phytoplankton in our oceans, so an explanation could be that the remote planet’s surface also contains warm water “teeming with life”. And the compound contains three of the CHNOPS elements considered to be the building blocks of life. Methane and Carbon Dioxide have also been detected using the infra-red spectrum of the James Webb telescope which itself orbits the Sun..
If the DMS does indeed come from phytoplankton, the significance is that these microorganisms are called the “lungs of the earth” and perform photosynthesis in our oceans, absorbing carbon dioxide and producing oxygen for our atmosphere and glucose for the food chain – for instance whales consume them..
These plankton may not have been the very first photosynthesisers – that accolade belongs to cyanobacteria – but they may have been the second group and indeed many plankton are eukaryotic cells with a nucleus and chloroplasts making them plant-like.
So in summary, the link is that if Dimethyl Sulphide (and also Dimethyl Disulphide) have been detected on planet K2-18b, this indicates the presence of phytoplankton, which in turn suggests the process of photosynthesis, which is the fundamental biological process on our own earth – and so why not also on Planet K2-18 b?
But there’s always a however…
But hold on – there are some doubts, even amongst the astronomers. First, the probability of the detection being pure chance is low at 0.3% but not yet low enough. A-Level Maths and Biology students will be familiar with the 5% confidence limit in Hypothesis testing but in this instance a much stricter and lower confidence limit is apparently needed, namely 0.00006% or five standard deviations, and more observations are needed to reach such a tiny probability of the detection being merely a “false flag”.
Additionally, Biology students will be familiar with the concept of Biotic and Abiotic factors. In theory the only way DMS can be produced is through a Biotic process, namely a Biological life-confirming reaction such as photosynthesis. But we can’t entirely discount the possibility of DMS simply being produced by an obscure Abiotic (non-biological) process) on a planet whose conditions, after all, we know relatively little about. Also, DMS is a chemical which breaks down very quickly in an atmosphere and the products of that breakdown such as hydrogen sulphide have not been definitively detected at K2-18b.
Further, to what extent does plankton actually constitute “life”? There is a multi billion year route with many hurdles to overcome which makes the transition from plankton to humans far from inevitable.
Always end with a song…
So it is fair to say that the jury is “still out”, but nevertheless this is an exciting development in the quest to answer the famous question, is there alien life out there? Not perhaps, as David Bowie might say, Life on Mars, but probably plankton on Planet K2-18 b.