Life, or at least life as we know it, strongly depends on a planet's position around a star. The planet needs to belong to the habitable zone, but new research suggests that this favorable region can be extended with a little help from volcanos.
Researchers at Cornell University have looked at how volcanic activity could affect the atmosphere and habitability of an exoplanet. They discovered that hydrogen spewed by volcanos could expand the habitable zone by 30 to 60 percent. Their findings are reported in the Astrophysical Journal Letters.
Hydrogen combined with other gas like water vapor and carbon dioxide could generate sufficient atmospheric warming for life to evolve. An Earth-sized planet can only hold onto atmospheric hydrogen for a few million years, but continuous and copious volcanic activity might maintain a high density of hydrogen.
“We just increased the width of the habitable zone by about half, adding a lot more planets to our ‘search here’ target list,” lead author Dr Ramses Ramirez said in a statement. “You get a nice big warming effect from volcanic hydrogen, which is sustainable as long as the volcanoes are intense enough.”
If this was applied to the Solar System, the habitable zone would extend all the way into the asteroid belt. However, there's no volcanically active planet in this region apart from Earth.
Recently, astronomers have announced seven Earth-size planets in the TRAPPIST-1 system, three of which (TRAPPIST-1 e, f, and g) reside in the habitable zone. This study's results have important ramifications for our search for life in this system. A fourth planet, TRAPPIST-1 h, would be included in the extended habitable zone if it were to have volcanos.
“Finding more rocky planets in the habitable zone – per star – increases our odds of finding life,” co-author Professor Lisa Kaltenegger added. “Although uncertainties with the orbit of the outermost Trappist-1 planet ‘h’ means that we’ll have to wait and see on that one.”
Hydrogen has another important property that’s useful for astronomers. It puffs up planetary atmospheres, making them easier to be studied. That will make it easier for the next generation of observatories like the James Webb Space Telescope or the European Extremely Large Telescope to discover molecules related to life like methane or ozone.