Hunting for habitable exoplanets now may be easier: Cornell astronomers report that hydrogen pouring from volcanic sources on planets throughout the universe could improve the chances of locating life in the cosmos.
Planets located great distances from stars freeze over. 鈥淥n frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes,鈥 said lead author , research associate at Cornell鈥檚 . 鈥淏ut if the surface is warm enough 鈥 thanks to volcanic hydrogen and atmospheric warming 鈥 you could have life on the surface, generating a slew of detectable signatures.鈥
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 percent, according to this new research. 鈥淲here we thought you would only find icy wastelands, planets can be nice and warm 鈥 as long as volcanoes are in view,鈥 said , Cornell professor of astronomy and director of the Carl Sagan Institute.
Ramses Ramirez, research associate at Cornell鈥檚 Carl Sagan Institute, left, and Lisa Kaltenegger, professor of astronomy and director of the Sagan Institute.
Their research, 鈥淎 Volcanic Hydrogen Habitable Zone,鈥 is published today in The Astrophysical Journal Letters.
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.
鈥淵ou get a nice big warming effect from volcanic hydrogen, which is sustainable as long as the volcanoes are intense enough,鈥 said Ramirez, who suggested the possibility that these planets may sustain detectable life on their surface.
A very light gas, hydrogen also 鈥減uffs up鈥 planetary atmospheres, which will likely help scientists detect signs of life. 鈥淎dding hydrogen to the air of an exoplanet is a good thing if you鈥檙e an astronomer trying to observe potential life from a telescope or a space mission. It increases your signal, making it easier to spot the makeup of the atmosphere as compared to planets without hydrogen,鈥 said Ramirez.
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鈥檚 habitable zone reach to 2.4 times the Earth-sun distance 鈥 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.
鈥淲e just increased the width of the habitable zone by about half, adding a lot more planets to our 鈥榮earch here鈥 target list,鈥 said Ramirez.
Stellar temperature versus distance from the star compared to Earth for the classic habitable zone (shaded blue) and the volcanic habitable zone extension (shaded red). Credit: Ramses Ramirez
Atmospheric biosignatures, such as methane in combination with ozone 鈥 indicating life 鈥 will likely be detected by the forthcoming, next-generation James Webb Space Telescope, launching in 2018, or the approaching European Extremely Large Telescope, first light in 2024.
NASA reported Feb. 22 finding seven Earth-like planets around the star Trappist-1. 鈥淔inding multiple planets in the habitable zone of their host star is a great discovery because it means that there can be even more potentially habitable planets per star than we thought,鈥 said Kaltenegger. 鈥淔inding more rocky planets in the habitable zone 鈥 per star 鈥 increases our odds of finding life.鈥
With this latest research, Ramirez and Kaltenegger have possibly added to that number by showing that habitats can be found, even those once thought too cold, as long as volcanoes spew enough hydrogen. Such a volcanic hydrogen habitable zone might just make the Trappist-1 system contain four habitable zone planets, instead of three. 鈥淎lthough uncertainties with the orbit of the outermost Trappist-1 planet 鈥榟鈥 means that we鈥檒l have to wait and see on that one,鈥 said Kaltenegger.
The Simons Foundation and the Cornell Center for Astrophysics and Planetary Science funded this research.
This article also appears in the .
Dozens of news outlets have covered this research, including , , , and .
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