NASA's Hubble Telescope Detects Water Vapour In Small Exoplanet's Atmosphere

Astronomers using NASA's Hubble Space Telescope have detected water molecules in the atmosphere of a small,blazing-hot exoplanet 97 light-years from Earth. The planet, named GJ 9827d, is approximately twice Earth's diameter and could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy.

"This would be the first time that we can directly show through atmospheric detection, that these planets with water-rich atmospheres can exist around other stars," said team member Bjorn Benneke of the Trottier Institute for Research on Exoplanets at Universite de Montreal. "This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets."

"Water on a planet this small is a landmark discovery," added co-principal investigator Laura Kreidberg of Max Planck Institute for Astronomy in Heidelberg, Germany. "It pushes closer than ever to characterizing truly Earth-like worlds."

Water is essential for life, but the exoplanet is unlikely to host any type of life due to its searing temperatures that would turn a water-rich atmosphere into steam. However, astronomers have yet to uncover the truth of this unusual world's atmosphere. 

The findings of the study appeared in a report published on Thursday in The Astrophysical Journal Letters.

Currently, the research team can't tell whether Hubble picked up on water vapour traces within a puffy, hydrogen-rich atmosphere or the planet has a water-rich atmosphere because the host star evaporated GJ 9827d's original hydrogen and helium atmosphere.

"Our observing program, led by principal investigator Ian Crossfield of Kansas University in Lawrence, Kansas, was designed specifically to not only detect the molecules in the planet's atmosphere but to look specifically for water vapour. Either result would be exciting, whether water vapour is dominant or just a tiny species in a hydrogen-dominant atmosphere," said the science paper's lead author, Pierre-Alexis Roy of the Trottier Institute for Research on Exoplanets at Universite de Montreal.

"Until now, we had not been able to directly detect the atmosphere of such a small planet. And we're slowly getting in this regime now," added Benneke. "At some point, as we study smaller planets, there must be a transition where there's no more hydrogen on these small worlds, and they have atmospheres more like Venus (which is dominated by carbon dioxide)."

Because the planet is as hot as Venus, at 800 degrees Fahrenheit, it definitely would be an inhospitable, steamy world if the atmosphere were predominantly water vapour, NASA said in a release. 

At present the team is left with two possibilities. One scenario is that the planet is still clinging to a hydrogen-rich atmosphere laced with water, making it a mini-Neptune. Alternatively, it could be a warmer version of Jupiter's moon Europa, which has twice as much water as Earth beneath its crust." The planet GJ 9827d could be half water, half rock. And there would be a lot of water vapour on top of some smaller rocky body," said Benneke.