Hycean planets: a new hope for humanity?

There seem to be two sides to every discussion about discovering habitable planets in space. Are we excited to find new planets because we want to find signs of extraterrestrial life? Or are we starting the real-estate hunt for a new home once ours is destroyed?

In either case, there is one very important factor: water. Finding signs of water on a planet has long been an important sign that scientists are paying close attention to. This past month, the James Webb Space Telescope found possible signs of water on a planet called K2-18b.

K2-18b is 8.6 times as large as Earth — it's huge! What originally made K2-18b appeal to researchers was data from the Hubble Space Telescope suggesting the existence of water vapor in the atmosphere. The planet has been compared to Neptune, which has oceans floating above massive sheaths of ice. Furthermore, K2-18b orbits in the habitable zone of its “sun” — a star called K2-18. The habitable zone refers to the distance from the central star in a solar system at which life can typically be sustained on a planet. This relies on a number of factors, including temperature and geology. In order to understand the role of water on this planet, the Webb Space Telescope had to find much more specific information about the chemical makeup of its atmosphere.

After new data was collected, K2-18b was labeled a "Hycean" planet, which means it has hydrogen in its atmosphere in addition to likely having oceans. The Webb Space Telescope also found signs of other key chemical components in K2-18b’s atmosphere — carbon dioxide, methane, and dimethyl sulfide. Carbon dioxide and methane both have strong links to life, but scientists suggest that dimethyl sulfide is created solely by living organisms, at least on Earth. This might lead scientists to the conclusion that K2-18b is inhabited by something that is producing the dimethyl sulfide that we see in its atmosphere.

These discoveries sound really exciting, but before you start hypothesizing about how many legs these new aliens have, consider that on Earth, the majority of the dimethyl sulfide in our atmosphere comes from phytoplankton, which are hardly the pinnacle of conscious life in our world. Additionally, it is not known exactly what temperature K2-18b’s oceans are — they may not be able to sustain life as we know it.

Still, these early findings are indicative of more to come, especially with new technology like the Webb Telescope providing us with levels of detail we did not have access to in the past. K2-18b is not the only planet to show signs of habitability — Joey Rodriguez, a professor at Michigan State University working with a team of NASA scientists, discovered a new planet, TOI-700, in January of this year in the habitable zone of its solar system. As far back as 2004, the Hubble Telescope found a planet called HD 209458b with carbon dioxide and oxygen in its atmosphere.

NASA has a tool that allows you to see all of the planets we have discovered outside of our solar system. If you use it, the first thing you’ll notice is that there are quite a lot of them. We still have so much to learn and find; K2-18b is just the intriguing tip of a very large iceberg. Once we know for sure that we’ve found life, the questions will evolve: should we go visit? And if we do, will we want to stick around?