Researchers at the University of Cambridge, UK, suggest that the search for planets with life should not be limited to worlds similar to ours, and believe that a particular category of these objects is a candidate for the first detection of biosignals: the hyceanic planets.
Strange name, right? It took me a while to understand where it came from. Hang in there when I get there. Much has been said about oceanic planets, which would be slightly larger than the Earth and completely covered by thick layers of water, capable of making our seas look like swimming pools.
And then the next category, hitherto little prestigious, would be composed of even larger planets, which, in addition to being rich in water, would have extensive atmospheres dominated by hydrogen, similar to those of gas giant planets.
In both cases, we are talking about worlds with an intermediate size between Earth (the largest of the rocky solar worlds) and Neptune (the smallest of the gaseous ones, with a diameter about four times larger than Earth’s). There is nothing like this in the Solar System, but astronomers have found hundreds of planets with diameters in this intermediate range, and they are generally referred to as super-earths (up to 60% larger in diameter than Earth) or mini-neptunes (if greater than 60%).
Until recently, despite being more numerous than super-earths, mini-neptunes were considered poor candidates for harboring life. It was speculated that the pressure and temperature under its hydrogen-rich atmosphere were too high to allow life to exist.
The game started to turn last year, when Nikku Madhusudhan’s team in Cambridge showed in a study published in Astrophysical Journal Letters that the mini-neptune K2-18b, discovered by NASA’s Kepler satellite, despite being 2, 6 times larger than Earth, it could, in theory, have a habitable ocean beneath its hydrogenated atmosphere. Hydrogen+oceanic, hyceanic. Frog.
Now, in a new article, this time in the Astrophysical Journal, Madhusudhan and his colleagues Anjali Piette and Savvas Constantinou present the category of hyceanic planets more broadly. In theory, worlds up to 2.6 times the Earth’s diameter can keep habitable conditions, and the so-called habitability zone (region around the star in which the amount of radiation is compatible with the existence of stable water bodies in a planet) would be much wider for these worlds than for terrestrial analogues.
And what’s most exciting is that many of the potential Heceanic planets could have their atmosphere studied in detail very soon by the James Webb Space Telescope, which NASA hopes to launch by year’s end. Observations from the K2-18b, by the way, are already scheduled to be among the first to be carried out by the new satellite.
This column is published on Mondays in Folha Corrida.
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