Astronomers using the Hubble Space Telescope have detected a water-rich atmosphere around a six billion-year-old world. It’s just 97 light-years from the solar system.
GJ 9827d is an exoplanet—a planet that orbits a star other than our sun—about twice the diameter of Earth that resembles both Neptune and Venus in the solar system, according to NASA. It’s the smallest exoplanet where water vapour has been detected in the atmosphere.
Landmark Moment
The discovery of water on GJ 9827d, in the constellation Pisces, is a landmark moment. “It pushes us closer than ever to characterizing truly Earth-like worlds,” said Laura Kreidberg, director of the Atmospheric Physics of Exoplanets department at the Max Planck Institute for Astronomy in Heidelberg, Germany, in a press release. This detection of water vapor could represent a breakthrough in understanding water-rich worlds elsewhere in the galaxy. That’s because the presence of water on other planets is considered a crucial factor in determining the potential for life.
“This would be the first time that we can directly show through atmospheric detection, that these planets with water-rich atmospheres can actually exist around other stars,” said team member Björn Benneke of the Trottier Institute for Research on Exoplanets at Université de Montréal, Canada. “This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets.” The research paper was published today in The Astrophysical Journal Letters.
Steamy World
The planet’s proximity to its host star means it may be a steamy world with temperatures as hot as Venus. However, scientists have yet to determine whether the planet’s atmosphere is mostly water or a puffy hydrogen-rich atmosphere. The problem with GJ 9827d is its age and closeness to its star. At six billion years old, GJ 9827d should have lost most of its primordial hydrogen due to intense irradiation from its star. “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,” said Benneke.
Half Water, Half Rock
There are other possibilities, too. It’s thought that GJ 9827d could still hold onto a hydrogen-rich envelope laced with water, making it a mini-Neptune. Alternatively, it could be more like 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,” said Benneke. “And there would be a lot of water vapor on top of some smaller rocky body.” If the planet has a residual water-rich atmosphere, it must have formed farther away from its host star and migrated closer to the star.
The scientists will soon know much more because they’ve just had James Webb Space Telescope recently observe GJ 9827d. “We can hardly wait to see what those data reveal,” said Kreidberg. “Hopefully, we can now settle the question of water worlds once and for all.”
Wishing you clear skies and wide eyes.
