'Planets with volcanic hydrogen likely to support alien life'

Hunting for habitable worlds now may be easier than before, say scientists who suggest that exoplanets with hydrogen pouring from volcanic sources may have a warmer atmosphere and provide a better target to find alien life in the universe.

Combining the greenhouse warming effect from hydrogen, water and carbon dioxide on planets sprinkled throughout the cosmos, distant stars could expand their habitable zones by 30 to 60 per cent, researchers said.

Such a volcanic hydrogen habitable zone may mean that the Trappist-1 system - the recently discovered system of seven planets - contains four habitable zone worlds, instead of three.

Planets located great distances from stars freeze over, researchers said. "On frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes," said Ramses Ramirez, research associate at Cornell University in the US.

"But if the surface is warm enough - thanks to volcanic hydrogen and atmospheric warming - you could have life on the surface, generating a slew of detectable signatures," said Ramirez.

"Where we thought you would only find icy wastelands, planets can be nice and warm - as long as volcanoes are in view," said Lisa Kaltenegger, professor at Cornell.

The idea that hydrogen can warm a planet is not new, but an Earth-like planet cannot hold onto its hydrogen for more than a few million years. Volcanoes change the concept.

"You get a nice big warming effect from volcanic hydrogen, which is sustainable as long as the volcanoes are intense enough," said Ramirez, who suggested the possibility that these planets may sustain detectable life on their surface.

A very light gas, hydrogen also "puffs up" planetary atmospheres, which will help scientists detect signs of life. "Adding hydrogen to the air of an exoplanet is a good thing if you're an astronomer trying to observe potential life from a telescope or a space mission," said Ramirez.

"It increases your signal, making it easier to spot the makeup of the atmosphere as compared to planets without hydrogen," he said. In our solar system, the habitable zone extends to 1.67 times the Earth-Sun distance, just beyond the orbit of Mars.

With volcanically sourced hydrogen on planets, this could extend the solar system's habitable zone reach to 2.4 times the Earth-sun distance - about where the asteroid belt is located between Mars and Jupiter.

This research places a lot of planets that scientists previously thought to be too cold to support detectable life back into play. "We just increased the width of the habitable zone by about half, adding a lot more planets to our 'search here' target list," said Ramirez.