‘Strongest evidence yet’ of life found on distant planet

On Wednesday, a mysterious email arrived in the inboxes of the Cambridge university astrophysics students, revealing there was to be a 'big announcement' from our department the next day. On reading BBC Science, and seeing some astrophysics articles in national newspapers the next morning, we were gobsmacked to find out that a research team at the Institute of Astronomy in Cambridge had found the most promising signs yet of life elsewhere in the universe.

Yes, you read that correctly! While the tabloids predictably splashed cartoon green aliens on their front pages, the details are, however, a bit more complicated than The Sun, which is not famed for its scientific prowess, might have us believe.

So, what exactly has been found and what is the fuss all about?

Exoplanets are planets orbiting stars other than our own, the Sun (as in the star not the newspaper!), meaning they have their own version of our solar system. Exoplanets can be detected in various ways, but the most common is the transit method, where a star is observed and eventually a planet passes in front of it, blocking a small fraction of the star's light when observed by a telescope. When a graph of stellar brightness is plotted against time, as shown below, the curve shows a dip for the time during which the starlight is partially obscured by the planet. From the size of the brightness dip, the size of the planet can be worked out, provided the star's size is known, which itself is found through other independent means. The thin atmosphere of a planet is also visible as we watch it pass in front of its host star, and from this the chemical species within its gas can be investigated.

How the transit method of exoplanet detection works. Credit: NASA/JPL

The planet in question is called K2-18b, which orbits its host star called K2-18. At a distance of just over 700 trillion miles away, this system is close by in astronomical terms. There is some spirited debate in the planetary community about what kind of planet this might be, my personal favourite being the 'hycean world' hypothesis: an ocean covered world with a thin, mainly hydrogen atmosphere, which sounds rather exotic.

The big fuss is that the Webb telescope has detected molecules in the planet's atmosphere which, as far as currently known, can only be produced by living organisms: dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). On Earth, these are produced by marine dwelling plankton and bacteria. The amount of gas estimated in this planet's atmosphere is thousands of times higher than that on Earth, meaning that if the association of these gases with life is true, in the words of project leader Prof Madhusudhan, the planet would be 'teeming with life'.

Just let that sink in. Perhaps we are not alone in the galaxy, never mind the universe, which spans vast numbers of galaxies, each with vast numbers of stars potentially hosting planets. If it can be confirmed that this planet does indeed host life, there could be several others which also do so. Is life common in the universe? Could there even be an Earth twin? Or perhaps more fascinating still, other types of life we don't even know exist?

DMS and DMDS are currently thought to be produced only by biotic means, a fancy way of saying by living organisms. So, either we have discovered life on another planet for the first time, or, less excitingly but still scientifically interesting, we have found a new way of making these chemicals through abiotic (non-life) means.

An artist impression of the planet K2-18b as an ocean world with a thin hydrogen rich atmosphere. Credit: Cambridge University

It is hard to overestimate just how much excitement there has been, at least in the science community, about this. Researchers on the project state that the signal will be confirmed for sure within the next year or two. While the astronomers continue to pore over the data, other scientists are working in labs to determine if these chemicals can be produced by non-living means.

The reasoning for K2-18b potentially being an ocean world is the lack of detection of ammonia in its atmosphere, which it is thought could be absorbed by a large body of water. A competing theory is that the lack of ammonia could be explained by the planet being an ocean of molten rock, which would preclude life. Yet another theory suggests that this planet may be a mini gas giant with no surface at all. Whatever the case may be, it's been a thrilling week, not only because of a potentially monumental discovery, but also because I've rather enjoyed seeing generally reserved astronomers and professors strike up spirited debates about the nature of what exactly has been found. I am a mere student of this fine subject that several wiser and cleverer people before me have studied for their whole lives, but, as the saying goes*, 'here is my 50p': given the enormity, even infinity, of the universe, with its mind boggling huge number of galaxies each with billions of stars, many of which could have planets, does it not seem a tad arrogant to think we are entirely unique in life and completely alone in the universe? Human brains struggle with big numbers, and the concept of infinity is certainly a tricky one. Even accounting for the statistics where several things, some unlikely, need to happen in sequence for life to form, if there are, say, trillions of planets, even if only a tiny percentage of them could host life, that is still more than one planet? My personal view is there is life out there, but not in a way that we necessarily know it to exist, and as such we may not have the tools to detect it. Furthermore, given the vastness of the universe, it may well be that any life is too far away to detect. Currently, only planets orbiting stars in our own galaxy the Milky Way can be detected with the transit method, limiting our observations to just one galaxy out of billions or more. I find it rather comforting to believe we are not unique and there are other planets buzzing with life out there, I for one hope that if this is true, they can be found soon! How incredible it would be to look up at the night sky, knowing for the first time, that it is alive.

*I believe this is a British saying, which means 'here are my thoughts on the matter', similar to the question 'Penny for your thoughts?' presumably where someone would give you a penny in return for a thought?

Along with many other avid astrophysicists, I will be keeping a close eye on any updates on the matter and will spring to action on the blog when the next batch of findings are released.