What planets are potentially habitable? This recent study shakes our current knowledge about what we believe could be a potentially habitable planet, that is, in which the ideal conditions for the presence of liquid water were given.
A team of researchers from the University of Bern, the University of Zurich and the National Center of Competence in Research (NCCR) PlanetS claims that liquid water (recall that life on Earth began in the oceans ), could also exist for thousands of years. of millions of years on planets that are very different from Earth. And it is that, in the long term, liquid water does not necessarily have to appear in circumstances similar to those of the Earth; favorable conditions could even exist for billions of years on planets that barely resemble our original blue world.
“One of the reasons water can be liquid on Earth is because of its atmosphere,” explains study co-author Ravit Helled, professor of theoretical astrophysics at the University of Zurich and NCCR PlanetS member. “With its natural greenhouse effect , it traps just the right amount of heat to create the right conditions for oceans, rivers and rain,” says the expert.
Liquid water
Billions of years ago, as hydrogen and helium gases were readily available in the planet-forming materials around young stars, all planets built atmospheres dominated by these two elements. “When the planet first formed from cosmic gas and dust, it assembled an atmosphere consisting mainly of hydrogen and helium, the so-called primordial atmosphere,” said study author Ravit Helled of the University of Zurich.
But in our solar system, the rocky planets lost this atmosphere in favor of heavier elements, like oxygen and nitrogen on Earth. However, astronomers suggest that large rocky exoplanets at some distance from their star could retain their hydrogen- and helium-dominated atmospheres and could harbor liquid water on their surface.
With this, some planets in the universe could be even more habitable than our home planet, hosting a wider variety of organisms. The authors say that these super-Earths likely “bear little resemblance to our home planet” and may support organisms at very high pressures. “Life on the type of planet described in this paper would live in considerably different conditions than most life on Earth,” the scientists say.
“The surface pressures in our results are of the order of 100 to 1000 bar, the pressure range of the ocean floors and trenches. There is no theoretical pressure limit for life, and some of the most extreme examples in the Earth’s biosphere thrive at around 500 bar .
For the research, the team modeled nearly 5,000 exoplanets , some bound to their star and others free-floating, and simulated their development over billions of years. They took into account not only the properties of the planets’ atmospheres, but also the intensity of radiation from their respective stars, as well as the planets’ internal heat radiating outward.
The findings suggest that, depending on the planet’s mass and distance from its star, these planets could maintain a warm surface environment for 8 billion years, provided the atmosphere is thick enough (100 1,000 times larger than Earth).
“What we found is that, in many cases, the primordial atmospheres were lost due to intense radiation from stars, especially on planets that are close to their star,” said Marit Mol Lous, PhD student and lead author of the paper. . “But in cases where atmospheres remain, the right conditions for liquid water may exist. Perhaps more importantly, our results show that these conditions can persist for very long periods of time, up to tens of billions of years.” “.
Referencia: Marit Mol Lous, Potential long-term habitable conditions on planets with primordial H–He atmospheres, Nature Astronomy (2022). DOI: 10.1038/s41550-022-01699-8. www.nature.com/articles/s41550-022-01699-8
