Exoplanets, those beyond the Solar System, are one of astronomers’ main hopes for life. We have found about 4,400 to date, but too few similar to Earth in composition to think they can support life. Now a group of researchers has an interesting idea: What if exoplanets don’t have to be like Earth to host life? A new category of exoplanets, the “hyceans,” are more likely than others.
Since Earth is the only place we know for sure that harbors life, it is normal that we have searched space for planets or Earth-like places to find life. The Moon, Mars or satellites Titan and Europa are some of the candidates. Nevertheless, life has proven viable in the strangest places. For example, under polar ice or in extremely dry deserts.
Dense atmospheres, oceans and extreme temperatures
A place that is all ocean and has extreme temperatures does not sound particularly welcoming. Yet they are the kind of exoplanets that Cambridge astronomers have decided to investigate for life. These exoplanets are called mini-neptunes, and they are a category into which exoplanets fit with thick atmospheres, rocky or icy layers and, in some cases, water oceans. They are usually between 1.6 and 3.9 times the size of the Earth.
Mini-neptunes (so called because they are similar in composition to Neptune but smaller in size) have been known for some time. However, within this category there is a subclass of exoplanets that are hot (due to their proximity to the star they orbit) and have a hydrogen-rich atmosphere, as well as huge oceans on its surface (not necessarily water). Although the high temperatures and pressure of these places is not ideal for human life, it can host life from some bacteria and organisms that here on Earth have been shown to survive such conditions.
Astronomers have already found some examples of this type of exoplanets. One of them is K2-18b, discovered in 2017 and it is believed that there is water in it. Now the goal is to compile a list of these types of exoplanets to explore in the future.
What are astronomers looking for on these exoplanets? Mainly clues to the origin of life, molecular compositions that enhance the appearance of life, such as methyl chloride and dimethyl sulfide. These compositions can actually be “easily” detected with telescopes like the future James Webb, if they are found on these exoplanets.
Once James Webb begins operating in orbit, the researchers will analyze the list of potential hycean subclass exoplanets for these signs of life. All of those they have found are orbiting red dwarf stars and are less than 150 light-years away. We can forget for the moment the idea of visiting them, but we can better understand what conditions are required in other places in space for the appearance of organisms.
More information | University of Cambridge and arXiv