Recently, the world was introduced to a potential thrilling breakthrough for space science, when NASA’s latest great observatory, the James Webb Space Telescope (JWST), spotted something quite unexpected on a distant exoplanet called K2-18b.
K2-18b resides around 120 light years from Earth within the constellation of Leo, the Lion. It is what scientists call a “sub-Neptune” planet, meaning that it’s bigger than Earth but smaller than Neptune. It orbits its red dwarf star in what is known as the “habitable zone”, or more colloquially, the “goldilocks zone” – a sweet-spot around its star where temperatures could be just right for liquid water to exist. Planets falling within this area offer the greatest potential for astrobiologists when hunting for signs life.
K2-18b is thought to be a Hycean world; a world with a hydrogen-based atmosphere surrounding a global ocean of liquid water, devoid of any landmass. The presence of water is seen as a pre-requisite by many for life to exist (albeit life as we know it at least), making K2-18b a possible home for weird and wonderful alien life.
In April, JWST discovered the presence of a gas known as dimethyl sulphide, or DMS for short. Why is this exciting? Because the only place we know DMS comes from is…life. Here on Earth, this gas is made almost entirely by tiny sea creatures like phytoplankton. These microscopic organisms live in the oceans and, as they go about their business, they release DMS into the air. It’s even believed to help form clouds!
So, when scientists saw signs of this gas on another planet, eyebrows were definitely raised. Could this planet harbour a flourishing marine-based ecosystem?
You might be wondering: how can a telescope know what gases are floating around a planet that is 120 light-years away? Astronomy is ultimately the study of light, and examining the elemental constituents of a distant planet’s atmosphere is no different. When a planet passes in front of its star, some of the starlight shines through its atmosphere. Elements within it, block out certain wavelengths of light, producing a pattern akin to a barcode in the supermarket. By analysing these elemental fingerprints, scientists can simply read off a list of its ingredients.
The amounts found by JWST aren’t huge, but they still dwarf the amounts found on Earth. This has allowed us to detect it from this vast distance, and is certainly enough to get scientists very interested – could there be great colonies of alien phytoplankton floating around in the surface of this ocean world? The discovery doesn’t prove anything yet, but it’s one of the strongest hints we have ever had.
Before anyone gets too excited, it’s important to remember that this is still early science. More observations will be needed to confirm that the signal is real, and to rule out other explanations. Our understanding of life is based on a sample size of exactly…one. In a Universe of almost infinite possibilities, life on other planets may metabolise in very different ways, and there may be a multitude of ways to manufacture DMS from yet undiscovered geological processes.
Still, the idea that a distant planet might have oceans and even microscopic life is amazing. Just a few years ago, we were blissfully unaware of planets outside of our own solar system, let alone the makeup of their atmospheres. Now we have a catalogue of over 6000 confirmed alien worlds, and we are talking about decoding their oceans from across the galaxy!
Thanks to the James Webb Space Telescope, the search for life beyond Earth is heating up, and K2-18b has just jumped to the top of the watchlist.
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