A new study suggests that the search for alien life needs to broaden its horizons.
To date, alien hunters have mainly focused on Earthlike planets. This is a good place to start considering that Earth, which is rocky and water-covered, is the only world that has life. The universe is filled with many planets that may be habitable, even though they are not Earthlike.
Researchers have identified one class of alien planets called "Hycean", which is 2.5 times larger than Earth. They feature enormous oceans of liquid water under hydrogen-rich atmospheres. Study team members stated that Hycean planets are extremely abundant in the Milky Way galaxy and could be home to microbial life similar as the "extremophiles", which thrive in the harshest environments of Earth.
Nikku Madhusudhan (Institute of Astronomy, University of Cambridge, England) stated in a statement that "Hycean Planets open a whole new avenue for our search for life elsewhere."
Related: 10 exoplanets which could be home to alien life
Hycean worlds have similar sizes to the rocky "super-Earths" and gassy, "mini-Neptunes", two of the most popular types of exoplanets in the galaxy. According to the new study published in The Astrophysical Journal online on Wednesday, August 25, the Hyceans have densities that are comparable to those of mini-Neptunes and super-Earths.
They are also diverse. Some orbit so close that their stars are tidally locked. There's one dayside that is scorching hot and one nightside that is always dark. Some orbit far away and receive very little stellar radiation. However, life could still exist on these extreme Hyceans, researchers emphasize, for example, in nightside waters of tidally-locked worlds.
"It's thrilling that habitable conditions could exist upon planets so different than Earth," Anjali Piette, a study co-author from Cambridge's Institute of Astronomy said in the same statement.
Hyceans are also good places to look for biosignature gases like methane and oxygen.
The researchers said that they found biomarkers easier to detect in Hycean atmospheres due to the higher temperatures and larger radiuses permissible for Hycean worlds than in those of rocky exoplanets.
A hunt for Hycean life could begin soon. Madhusudhan and colleagues discovered a number Hycean worlds that could be studied by next-generation observatories like NASA's $9.8 million James Webb Space Telescope, which will launch later in the year. These potential targets orbit dim, small red dwarf stars that are between 35 and 150 light years from Earth.
Madhusudhan stated that a biosignature detection could transform our understanding about life in the universe. We need to be honest about where we think life will come from and what it could look like. Nature continues to amaze us in surprising ways.
