An illustration imagining the two Earth-sized exoplanets transiting their red dwarf host. Image Credit: NASA, ESA, and G. Bacon (STScI)
The Hubble Space Telescope has been used in the first search for atmospheres around Earth-sized exoplanets, and has revealed that two could potentially support life.
Astronomers pointed Hubble at a 500 million-year-old red dwarf star in the constellation of Aquarius to analyse the atmospheres of two exoplanets orbiting it: TRAPPIST-1b and TRAPPIST-1c.
They found that neither is likely to have the hydrogen-helium atmosphere usually found on gas planets like these, increasing the chances of either exoplanet being habitable.
The team behind the study were able to analyse the planets’ atmospheres at the same time because both planets passed in front of – or transited – their host star within minutes of each other.
By analysing the light from the star as it shone through the atmospheres, the team could glean information as to their atmospheric properties. This technique is known as spectroscopy.
“The lack of a smothering hydrogen-helium envelope increases the chances for habitability on these planets,” says team member Nikole Lewis of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.
“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.”
TRAPPIST-1b orbits its sun in 1.5 days, while TRAPPIST-1c orbits in 2.4 days.
Despite these longer orbital periods, the planets are between 20 and 100 times closer to the red dwarf than Earth is to the Sun.
And because the star is much fainter than our Sun, one or both of the exoplanets may be within the habitable zone, where liquid water could pool on the surface.
Observations will be carried out with future telescopes to search for signs of carbon dioxide, ozone, water vapour and methane.
“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,” says co-author Hannah Wakeford of NASA’s Goddard Space Flight Center.
“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,” says Geoff Yoder, acting associate administrator for NASA’s Science Mission Directorate in Washington.
“This is an exciting time for NASA and exoplanet research.”