Water vapour detected in small exoplanet's atmosphere

Astronomers have detected water vapour in the atmosphere of a small exoplanet, thanks to the razor-sharp vision of the NASA/ESA Hubble Space Telescope.

The exoplanet, GJ 9827d, was discovered by NASA's Kepler Space Telescope in 2017. Hubble observed the planet during 11 transits over three years. The rocky world, only about twice Earth's diameter, could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy.

The researchers are yet to confirm whether water vapour is dominant or just a tiny species in a puffy hydrogen-rich atmosphere.

Because the GJ 9827d is as hot as Venus, it definitely would be an inhospitable, steamy world if the atmosphere were predominantly water vapour, the researchers said.

The team is considering two potential scenarios regarding GJ 9827d. The planet could either possess a hydrogen-rich envelope with traces of water vapor, resembling a mini-Neptune or it could be a warmer version of Jupiter's moon Europa, which has twice as much water as Earth beneath its crust.

The researchers propose two theories:

If GJ 9827d possesses a residual water-rich atmosphere, then it must have formed farther away from its host star, where the temperature is very low and water exists in the form of ice than its present location. In this case, the planet would have moved closer to the star and received more radiation. The increased radiation could have also contributed to the heating and escape of hydrogen from the planet's atmosphere or is still in the process of escaping, the planet's weak gravity.

The alternative theory suggests that the exoplanet formed close to the hot star, with a trace of water in its atmosphere.

"This would be the first time that we can directly show through an atmospheric detection that these planets with water-rich atmospheres can actually exist around other stars. This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets," said team member Björn Benneke of the Université de Montréal.

💧New water detection!💧The NASA/ESA @HUBBLE_space telescope has detected water vapour in a small exoplanet's atmosphere. At only approximately twice Earth's diameter, the planet GJ 9827d could be an example of potential planets with water-rich atmospheres elsewhere in our… pic.twitter.com/FPxjuk1B7I

— ESA (@esa) January 25, 2024