Where do we start when looking for extraterrestrial life? Until now, scientists have focused on the most obvious: i identify planets with conditions similar to those found on Earth, mainly in terms of size, mass, temperature, and atmospheric composition. Now, a team of researchers from the University of Cambridge has presented an analysis that identifies a new class of exoplanets that also meet conditions that make them potentially suitable to host some type of microbial life, but that do not look at all like our planet. They have been called “non-national planets”, an expression that refers to their main characteristic: their atmospheres are rich in hydrogen and they are also covered with oceans. According to the researchers, these types of planets are more numerous and observable than those similar to Earth and therefore can greatly expand our possibilities of finding habitable planets and biomarkers beyond the limits of our Solar System.
According to the scientists, who publish their results in The Astrophysical Journal , these planets have a much wider habitable zone than those similar to Earth. Many of the main identified candidates of this type are larger and hotter than Earth, but still contain the characteristics necessary to host large oceans that could support microbial life similar to that found in some of the most extreme aquatic environments on the planet. Land.
Analyzing the mini Neptunes
Most of the exoplanets identified so far are larger than Earth or smaller than Neptune, and for that reason they are called “super Earth” or “mini Neptune”. Most mini-Neptunes are more than 1.6 times the size of Earth: smaller than Neptune but too big to have rocky interiors like Earth. Previous studies of such planets have found that the pressure and temperature below their hydrogen-rich atmospheres would be too high to support life.
However, by studying the mini Neptune planet K2-18b , the researchers discovered that, under certain conditions, these planets could be habitable.
The result led to a detailed investigation of the full range of planetary and stellar properties for which these conditions are possible, which known exoplanets can satisfy those conditions, and whether their biosignatures can be observable.
This is how the planets are made up
The research led the researchers to identify a new class of planets with massive oceans and hydrogen-rich atmospheres. Hanic planets can be up to 2.6 times larger than Earth and have atmospheric temperatures of up to nearly 200 degrees Celsius, depending on their host stars , but their oceanic conditions could be similar to those conducive to microbial life in the oceans of the earth. Such planets also include tidal-blocked “dark” doic worlds that may have habitable conditions only on their permanent night sides, and “cold” doic worlds that receive little radiation from their stars.
According to the authors, these worlds are likely fairly common, meaning that, until now, the most promising places to search for life in other parts of the galaxy might have gone unnoticed.
However, size alone is not enough to confirm whether a planet is haeanic: other aspects such as mass, temperature, and atmospheric properties are required for confirmation. When trying to determine what conditions are like on a planet many light years away, astronomers must first determine if the planet is in the habitable zone of its star and then look for molecular signatures to infer the atmospheric and internal structure of the planet. that govern surface conditions, the presence of oceans, and the potential for life.
Astronomers also look for certain biological signatures that could indicate the possibility of life: oxygen, ozone, methane, and nitrous oxide are some of the most common. There are also a number of other biomarkers, such as methyl chloride and dimethyl sulfide, which are less abundant on Earth, but may be promising indicators of life on planets with hydrogen-rich atmospheres where oxygen or ozone may not be as abundant. abundant.
“Essentially, when we have been looking for these various molecular signatures, we have focused on Earth-like planets, which is a reasonable place to start,” explains Nikku Madhusudhan of the Cambridge Institute of Astronomy and director of the research. “But we believe that the non-native planets are more likely to find various traces of biosignatures.”
” It’s exciting that habitable conditions exist on planets so different from Earth, ” explains co-author Anjali Piette. The larger sizes, higher temperatures, and hydrogen-rich atmospheres of the haeanic planets make their atmospheric signatures much more detectable than Earth-like planets.
The Cambridge team identified a sizable sample of potential worlds that are prime candidates for detailed study with next-generation telescopes, such as the James Webb Space Telescope (JWST), due to launch later this year. All of these planets orbit red dwarf stars 35 to 150 light years away. The planned JWST observations of the most promising candidate, K2-18b, could lead to the detection of one or more biological signature molecules.
“Detecting a biosignature would transform our understanding of life in the universe,” says Madhusudhan. “We need to be more open about where we hope to find life and what form that life might take, as nature continues to surprise us in ways that are often unimaginable.”
Referencia: Nikku Madhusudhan, Anjali A. A. Piette, and Savvas Constantinou. ‘Habitability and Biosignatures of Hycean Worlds.’ The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abfd9c
Text: Cambridge University
