Astronomers recently found two possibly habitable exoplanets using the National Aeronautics and Space Administration’s Hubble Space Telescope. They named these TRAPPIST-1b and TRAPPIST-1c, two Earth-sized planets that do not have the typical puffy, hydrogen-dominated atmospheres. They are located 40 light years from us.

“The lack of a smothering hydrogen-helium envelope increases the chances for habitability on these planets,” says researcher Nikole Lewis from the Space Telescope Science Institute (STScI) in Baltimore. “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 study was led by a Massachusetts Institute of Technology scientist Julien de Wit. The research team actually spotted the Earth-sized planets last year but the scientists were only able to analyze the atmospheres on May 4 of this year when the two planets crossed in front of their star within minutes of each other.

The star in question is a red dwarf aged 500 million years old. When the two exoplanets crossed its face, the starlight that got filtered through their atmospheres revealed that both contain low levels of atmospheric hydrogen and helium. Still, the team admits that their analysis of the planets’ atmospheres is still limited.

TRAPPIST-1b circles its red dwarf star in only 1.5 days while TRAPPIST-1c in 2.4 days. The distance of the exoplanets from their star is between 20 and 100 times the distance of our planet to the sun.

Compared to our sun, the exoplanets’ dwarf star is much fainter. The scientists speculate that TRAPPIST-1c is located within the habitable zone. This is the zone where moderate temperatures allow pooling of liquid water.

More studies on these two planets are still needed. The team hopes that they can find planets with thinner atmospheres with compositions heavier than hydrogen like on Earth and Venus through follow-up observations using Hubble.