The James Webb Space Telescope has completed observations of an exoplanet that may contain an ocean-covered surface underneath a hydrogen-rich atmosphere. This discovery provides a fascinating glimpse into a planet unlike anything in our Solar System, and raises interesting prospects about potentially habitable worlds elsewhere in the Universe.
The exoplanet is called K2-18 b, and it’s located about 120 light-years away from us in the constellation Leo. It is bigger than Earth, but not as big as Neptune, putting this exoplanet in a class called sub-Neptunes, one of the most common types of exoplanets we’ve found. It orbits a cool dwarf star called K2-18 in the habitable zone, which means it could have liquid water on its surface. But what’s really amazing is that Webb has detected methane and carbon dioxide in its atmosphere. These are carbon-bearing molecules that could indicate the presence of life, or at least some interesting chemistry.
Webb used its Near Infrared Spectrograph (NIRSpec) instrument to analyze the light coming from K2-18 b as it passed in front of its star. By looking at how the starlight changed as it filtered through the planet’s atmosphere, Webb could measure the amounts of different molecules in the air. This technique is called transit spectroscopy, and it’s one of the best ways to study exoplanet atmospheres.
The results showed that K2-18 b has a hydrogen-rich atmosphere with traces of methane and carbon dioxide. There was also a possible detection of another molecule called dimethyl sulfide (DMS), which on Earth is only produced by living organisms. DMS is emitted by phytoplankton in the oceans, and it helps form clouds and regulate the climate. Could K2-18 b have some kind of ocean life that produces DMS? Or is there another explanation for this mysterious molecule?
The discovery of methane and carbon dioxide in K2-18 b’s atmosphere is consistent with the idea that this planet could be a Hycean world. Hycean worlds are a class of exoplanets that have hydrogen-rich atmospheres and water-covered surfaces. They are different from Earth-like worlds, which have nitrogen-rich atmospheres and rocky surfaces. Hycean worlds could be promising targets for finding signs of life but we shouldn’t get too excited just yet.
While K2-18 b lies in the habitable zone, and is now known to harbor carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet’s large size — with a radius 2.6 times the radius of Earth, and almost 9 times its mass — means that the planet’s interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Hycean worlds are predicted to have oceans of water. However, it is also possible that the ocean is too hot to be habitable or even be in liquid state.
Of course, there are still many uncertainties and challenges in studying K2-18 b. Webb’s observations are only the first step in exploring this fascinating world, and more data and analysis are needed to confirm and refine the results. Astronomers are planning followup studies using the Mid-Infrared Instrument spectrograph on JWST that they hope will further validate their findings and provide new insights into the environmental conditions on K2-18 b.
These exciting results are the product of just two observations, and there are many more on the way. We will use the most advanced observatories on Earth and in space to study this planet in more detail. Our ultimate goal is to find an exoplanet with life on it. If such a world exists, and we can find it, we will have left the cosmic shores of our home and waded just a bit deeper into the universal ocean and found that we are not alone. And maybe, just maybe, we learn that the universe is teeming with life.