Rocky exoplanets with an atmosphere of hydrogen and helium gases could have liquid water on the surface, like Jupiter’s moon Europa, and could thus host life. The question is whether the surface water sticks around long on “cold super-Earths,” that are ten times the mass of our planet:
Now, new calculations described in a paper published Monday in the journal Nature Astronomy suggest that the surface conditions of these worlds could have been temperate for more than enough time for life—for 5 billion to 8 billion years. Earth is only about 4.5 billion years old, by comparison, and life emerged here about 3.7 billion years ago.Eva Botkin-Kowacki, “We may be underestimating how many cold, giant planets are habitable” at Popoular Science (June 29, 2022) The paper is open access.
The researchers note in their Abstract that “Cold super-Earths that retain their primordial, H–He-dominated atmosphere could have surfaces that are warm enough to host liquid water. This would be due to the collision-induced absorption of infrared light by hydrogen, which increases with pressure.”
These cold super-Earths may or may not be in the life-friendly habitable zone. If they are large enough, they might prevent the escape of insulating gases anyway.
The first exoplanet was identified in 1992. Now NASA has confirmed over 4,000 exoplanets, with thousands of other “candidates” awaiting confirmation (or disconfirmation) based on further evidence. The researchers believe that planets that fall into this class could host life even if they are far from their host star because they can hang onto hydrogen:
The trick is keeping that hydrogen gas around long enough for it to build up. It’s a particularly light element, so unless a planet is massive enough and has enough gravity to hold onto the gas, hydrogen will vanish into space. And if the planet is close to its star, the radiation can make those particles escape more quickly. The vast distance between these cold super-Earths and their stars could protect their hydrogen gas from being torn awayEva Botkin-Kowacki, “We may be underestimating how many cold, giant planets are habitable” at Popoular Science (June 29, 2022) The paper is open access.
The new James Webb Space Telescope is currently being tested on Jupiter and its moons, as a practice run for studying exoplanets in more detail:
Jupiter is a complex system full of mysteries, hosting realms of questions concerning the nature of its delicate rings, how its largest moons may harbor oceans of water or hidden volcanoes, and how massive storms like the Great Red Spot form in the giant planet’s turbulent atmosphere…
“Jupiter is so bright, and Webb’s instruments are so sensitive, that observing both, the bright planet and its fainter rings and moons, will be an excellent test of how to get the most out of Webb,” added de Pater, who is leading the study with Thierry Fouchet of the Observatoire de Paris.Elizabeth Howell, “Jupiter and its moons will be a ‘proving ground’ for the James Webb Space Telescope” at Space.com (July 8, 2022)
Happily, we can test many hypotheses now. Because we really do not know very much about how life began on Earth, we can afford to be open-minded about it too.
You may also wish to read: Why scientists think there might be life on Europa Jupiter’s moon Europa, somewhat smaller than Earth’s moon, may have surface water and organic chemicals, researchers say. Europa, despite being outside the conventional “habitable zone,” may be a better bet for life than Mars. The launch of the Clipper in 2024 will tell us more.