When it comes to tracking down signs of life on distant planets, astronomers have generally played it safe. They looked for planets the size of Earth, with Earth-like surface temperatures and Earth-like atmospheres.
But now a team of researchers from the University of Cambridge has identified a new class of habitable planets that could be a game-changer. Dubbed “Hycean” planets – meaning hot planets covered in oceans with atmospheres rich in hydrogen – the newly identified exoplanets are much more numerous and easier to spot than Earth-like planets.
And specifically, the hunt for Hycean planets could lead us to discover biosignatures of life outside our solar system in the next two or three years, they say.
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“The Hycean planets are opening up a whole new avenue in our search for life elsewhere,” said study director Dr Nikku Madhusudhan of the Cambridge Institute of Astronomy.
“Basically, when we researched these various molecular signatures, we focused on Earth-like planets, which is a good place to start. But we believe that the Hycean planets offer a better chance of finding multiple trace biosignatures. “
Hycean planets can be up to 2.6 times the size of Earth and have atmospheric temperatures reaching 200 ° C. However, their ocean conditions could be similar to those on Earth and therefore could potentially harbor microbial life. A significant proportion of the exoplanets discovered to date fall into this category.
The larger sizes, higher surface temperatures, and hydrogen-rich atmospheres of Hycean planets also make their atmospheric signatures much easier to detect than Earth-like planets.
When looking for signs of life on other planets, astronomers look at so-called biosignatures such as oxygen, ozone, methane, and nitrous oxide, all of which are present on Earth. There are also a number of other biomarkers, such as methyl chloride and dimethyl sulfide, which could suggest the existence of life on planets with hydrogen-rich atmospheres where oxygen and ozone can. not be so abundant.
“A biosignature detection would transform our understanding of life in the Universe,” Madhusudhan said. “We need to be open about where we expect to find life and what form that life might take, as nature continues to surprise us in ways that are often unimaginable.”
The team has identified a number of Hycean planets between 35 and 150 light years away that they hope will be prime targets for the next generation of space telescopes, like the James Webb Space Telescope (JWST), which is to be launched later. This year.
What does it mean if an exoplanet is “habitable”?
All the forms of life that we know depend on one essential component: liquid water. So, in the search for life, astronomers focus on planets where liquid water might exist, which they call “habitable.”
Each star has a “habitable zone”, also called a “Goldilocks zone”, where it is neither too hot nor too cold. A planet in the habitable zone gets the right amount of energy from the star to support liquid water. Closer to the star and water would boil, and further away it would freeze.
However, this does not guarantee that there would be liquid water on a planet in the habitable zone. The planet’s atmosphere could be too thick, further raising the temperature. And even if liquid water exists on the planet, habitable does not mean inhabited.