New class of planets with warm oceans could support life outside Earth

In their search for potentially habitable planets outside our solar system, astronomers looked for Earth-like exoplanets. Scientists now have a new class of habitable exoplanets to look for: the Hycean planets.

The name describes hot ocean-covered planets that have a hydrogen-rich atmosphere – and are much easier to find and observe than would-be twins from our own Earth. Learning more about the Hycean planets could help scientists find biosignatures, or signs of life, outside our solar system in the near future. The study was published on Wednesday (25) in The Astrophysical Journal.

“The Hycean planets open up a whole new path in our search for life elsewhere,” the study’s lead author, Nikku Madhusudhan, an expert in astrophysics and exoplanetary science at the Institute of Astronomy at Cambridge University, said in a statement.

There are more than 4,000 known exoplanets outside our solar system. They are considered potentially habitable when they are located in the habitable zone around orbiting stars. In this zone, the planet is the right distance from the star so that liquid water has a stable presence – and possibly supports life as we know it.

ocean worlds

Some of the Hycean planets are bigger and hotter than our planet. But researchers believe these planets have large oceans that could support the kind of life that began on the early Earth and can still be found in extreme ocean environments.

One of the most attractive features of these planets is the fact that they have a larger habitable zone than Earth or Earth-like planets – so they could still support life, although they exist outside the zone where our planet must be in order to maintain life. habitability.

Of the thousands of exoplanets discovered in the last 30 years, many are between the size of Earth and Neptune. Scientists use names like “Superearths” and “Mininetunes” to describe these planets, which can be rocky like Earth or ice giants like Neptune. Or they get in an in-between situation.

Mini-Neptunes are 1.5 times the size of our planet, so they’re still smaller than Neptune, but too big to have a rocky interior like Earth. Below their atmospheres, which are rich in hydrogen, the pressure and temperature are probably too great for life to support.

Recent research by Madhusudhan and his colleagues, however, has determined that this inhospitable nature is not always the case. Depending on conditions (including size, mass and temperature) some of these planets may be habitable.

promising planets

The study led to the new classification of the Hycean planets. They can reach up to 2.6 times the size of Earth and atmospheric temperatures of nearly 200 degrees Celsius. Underneath the hydrogen-rich atmosphere are oceans that span the entire planet – and there could be microbial life there.

Some of these planets may be tidal blocked, which means that they permanently have one side that receives daylight from the star they orbit and the other side is perpetually dark. In this case, tidal-blocked Hycean planets can only be habitable on one side.

Hycean planets are common among known exoplanets, but have not been studied as much as Superearths. Perhaps the answer to where life exists outside our Solar System lies within this already known range.

Understanding whether a planet within the habitable zone has the right ingredients for life means researching biosignatures like oxygen, methane, nitrous oxide and ozone, or biomarkers including methyl chloride and dimethyl sulfide – characteristics found on Earth.

“When we looked for these various molecular signatures, we focused on Earth-like planets, which is a reasonable place to start,” Madhusudhan said. “But we think the Hycean planets offer a better chance of finding lots of biosignature traits.”

Future telescopes, such as the James Webb Space Telescope, to be launched in October, will be able to peer into the atmosphere of exoplanets and help scientists learn more about their composition. The Hycean planets could be a promising target for observation. One such candidate, called K2-18b, could reveal biosignature molecules.

“It’s exciting that there can be habitable conditions on planets so different from Earth,” study co-author Anjali Piette, a doctoral student at the Cambridge Institute of Astronomy, said in a statement.

There are promising planets, both inside and outside our solar system. However, biosignatures have not yet been detected on a world outside Earth.

“A biosignature detection would transform our understanding of life in the universe,” said Madhusudhan. “We need to be open about where we hope to find life and what form that life can take, as nature continues to amaze us in ways that are often unimaginable.”

(Translated text. Click here to read the original in English).