Exoplanets could provide habitable conditions for billions of years, study suggests

Researchers from the University of Zurich, Switzerland, have suggested that large rocky exoplanets at some distance from their star could retain their hydrogen and helium-dominated atmospheres.

The study suggests that these planets can sustain temperate conditions and liquid water on their surface for long periods of time.

As hydrogen and helium gases were readily available in the planet-forming materials around young stars, all planets built up atmospheres that were dominated by these two elements.

In our own Solar System, rocky planets lost this atmosphere in favour of heavier elements, such as oxygen and nitrogen on Earth.

Marit Mol Lous and colleagues from the University of Zurich investigated the evolution of such planets. They modelled the duration that hydrogen and helium-rich exoplanets could host liquid water on their surface.

Their findings suggest that depending on the mass of the planet and how far away it is from its star, these planets could keep a temperate surface environment for as long as eight billion years, provided the atmosphere is thick enough – between a hundred and a thousand times thicker than the Earth’s atmosphere.

The study authors say: “This result suggests that the concept of planetary habitability should be revisited and made more inclusive with respect to the classical definition.”

The study – ‘Potential long-term habitable conditions on planets with primordial H–He atmospheres‘ – is published in the journal Nature Astronomy.

In November 2021, astronomers used Kepler data from a new planet-detection algorithm to identify 366 new exoplanets, including one planetary system that comprises a star and at least two gas giant planets.

Previous studies have also revealed an Earth-dwarfing exoplanet, which holds liquid water and has potentially habitable conditions, that could be capable of supporting alien life.

A Washington State University study published in 2020 identified two dozen ‘superhabitable’ planets outside our Solar System that may be better than Earth at supporting life, being typically older, larger, slightly warmer and possibly wetter. The study also suggested that life could more easily thrive on planets that circle more slowly changing stars with longer lifespans than our own Sun.