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New Class of “Hycean” Exoplanets May Feature Life

The new James Webb Telescope will enable much clearer resolution for the composition believed necessary for hosting life

A group of Cambridge astronomers, studying the more than 4000 confirmed exoplanets, think that hydrogen-rich planets may host life. These “Hycean” planets are more numerous than planets similar to Earth and are easier to observe, especially through the new James Webb telescope, to be launched later this year.

They are thought to be completely covered by oceans and are termed “mini-Neptune water worlds”:

Many of the prime Hycean candidates identified by the researchers are bigger and hotter than Earth, but still have the characteristics to host large oceans that could support microbial life similar to that found in some of Earth’s most extreme aquatic environments.

These planets also allow for a far wider habitable zone, or ‘Goldilocks zone’, compared to Earth-like planets. This means that they could still support life even though they lie outside the range where a planet similar to Earth would need to be in order to be habitable.

University of Cambridge, “New class of habitable exoplanets represent a big step forward in the search for life” at Phys.org (August 25, 2021) The paper requires a subscription.

Here’s a video summary:

These planets have not been studied much because it was assumed that they might not support life. The Cambridge astronomers are saying, don’t be too sure, especially if they are in potential habitable zones in relation to their star:

Hycean planets can be up to 2.6 times larger than Earth and have atmospheric temperatures up to nearly 200 degrees Celsius, but their oceanic conditions could be similar to those conducive for microbial life in Earth’s oceans. Such planets also include tidally locked ‘dark’ Hycean worlds that may have habitable conditions only on their permanent night sides, and ‘cold’ Hycean worlds that receive little radiation from their stars…

Astronomers also look for certain biosignatures which could indicate the possibility of life. Most often, these are oxygen, ozone, methane and nitrous oxide, which are all present on Earth. There are also a number of other biomarkers, such as methyl chloride and dimethyl sulphide, that are less abundant on Earth but can be promising indicators of life on planets with hydrogen-rich atmospheres where oxygen or ozone may not be as abundant.

University of Cambridge, “New class of habitable exoplanets represent a big step forward in the search for life” at Phys.org (August 25, 2021) The paper requires a subscription.

The discovery of extremophiles — life forms living under remarkably difficult conditions on Earth — may have resulted in second looks at the question of habitability.

A special focus of interest is a planet called K2-18b, which could change the picture:

Situated 124 light-years away in the constellation of Leo, K2-18b is a mini-Neptune planet orbiting a red dwarf star. JWST will definitely study its atmosphere and look for biosignatures because water vapor was discovered in its atmosphere.

However, it’s regarded by most astronomers as being too big to have a rocky interior like Earth, so very unlikely to host any kind of life. It’s also thought that the planet would have both a surface temperature and surface pressure too high to support life.

But Madhusudhan’s team found that in certain conditions K2-18b and planets like it could support life, specifically by because they may host other biomarker molecules like methyl chloride and dimethyl sulphide.

Jamie Carter, “Is Alien Life Hiding In Plain Sight? New Class Of ‘Hycean’ Planet Is Where We Should Look, Say Scientists” at Forbes (August 25, 2021)

The new James Webb Telescope will give astronomers a chance to test many ideas.

You may also wish to read:

If we find life on exoplanets, some of it might be “crabs.” Over millions of years, many crustaceans gradually grew to look more and more like crabs, a process called convergent evolution. In an environment similar to Earth’s, we might expect life forms to converge on similar solutions. “Crabbiness” might be one of them.


Veteran science writer says we won’t meet intelligent aliens. Not because they are not there but because vast interstellar distances make them unreachable. While more people accept the idea of ET on exoplanets, Proxima Centauri is four light years away. Across the galaxy? That’s over 100,000 light years away.

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New Class of “Hycean” Exoplanets May Feature Life