NASA has discovered signs that two Earth-sized planets 40 light years away could be habitable.
During an exploration using the Hubble Space Telescope, scientists determined that the atmospheres of the two planets were unlikely to be dominated by hydrogen, which often prevents life from forming.
Nikole Lewis of the Space Telescope Science Institute (STScI) in Baltimore said: “The lack of a smothering hydrogen-helium envelope increases the chances for habitability on these planets.
“If they had a significant hydrogen-helium envelope, there is no chance that either one of them could potentially support life because the dense atmosphere would act like a greenhouse.”
The team observed the planets, TRAPPIST-1b and TRAPPIST-1c, in near-infrared light, before using a spectroscopy to decode the light, revealing suggestions about how the atmosphere might be made up.
NASA doesn’t yet know the content of the atmosphere, but scientists are excited about the implications of the low concentrations of hydrogen and helium.
The agency’s Geoff Yoder said: “These initial Hubble observations are a promising first step in learning more about these nearby worlds, whether they could be rocky like Earth, and whether they could sustain life.
“This is an exciting time for NASA and exoplanet research.”
The two planets orbit a star at distance between 20 and 100 times closer than the Earth to the sun. But the red dwarf star, which is at least 500 million years old, is believed to be much dimmer than our star, meaning at least one of the planets could orbit within the star’s habitable zone.
The zone is believed to enjoy moderate temperatures, potentially facilitating the formation of liquid water pools.
In May, the two planets crossed the face of their star within minutes of each other, providing indicators of the planets’ atmospheres.
Researchers now hope to use the telescope to search for the kind of thinner atmospheres found surrounding Earth and Venus.
NASA’s Hannah Wakeford said: “With more data, we could perhaps detect methane or see water features in the atmospheres, which would give us estimates of the depth of the atmospheres.”
In October 2018, NASA will launch the James Webb Space Telescope, which is promised by the agency to become the premier observatory of the next decade.
The telescope will help scientists to discover the full composition of the atmospheres and search for traces of carbon dioxide, ozone, water vapour and methane.
MIT’s Julien de Wit, who led the study, said: “These Earth-sized planets are the first worlds that astronomers can study in detail with current and planned telescopes to determine whether they are suitable for life.
“Hubble has the facility to play the central atmospheric pre-screening role to tell astronomers which of these Earth-sized planets are prime candidates for more detailed study with the Webb telescope.”