NASA’s Hubble Space Telescope has detected water vapor in the atmosphere of a small, steamy exoplanet, potentially illustrating water-rich worlds across our galaxy.
The planet GJ 9827d exceeds Earth’s diameter by only twice. At scorching 800°F, it resembles a steamy Venus.
“GJ 9827d could be half water, half rock with lots of water vapor atop a smaller rocky body,” said Björn Benneke of Montreal’s Trottier Institute for Exoplanet Research.
Astronomers including Laura Kreidberg and Thomas Mikal-Evans of Germany’s Max Planck Institute used Hubble to observe the exoplanet 97 light-years away.
“This would be the first atmospheric detection directly showing water-rich planets can exist around other stars,” Benneke said. “An important step toward characterizing Earth-like worlds.”
Kreidberg, co-lead of Hubble’s exoplanet program, agreed: “Water on such a small planet is a landmark find, pushing closer to truly Earth-like worlds.”
Observations spanned three years and 11 transits when the planet crossed its star. Scientists weren’t yet certain if Hubble spotted minimal water vapor in a hydrogen atmosphere. But if the atmosphere is mostly water left over from dissipated hydrogen/helium, that would be exciting too, said lead author Pierre-Alexis Roy of Montreal.
“Either result would excite us – water vapor dominant or just a trace in hydrogen atmosphere.”
GJ 9827d likely lost original hydrogen from intense radiation, leaving an atmosphere now dominated by water vapor. No hydrogen signatures have been found so far.
The water discovery provides insight into diverse, watery exoplanets. Hubble observed starlight passing through the planet’s atmosphere during transits, revealing water’s spectral fingerprint.
The planet may have a residual water atmosphere, hinting it formed farther out and migrated in. Or it could be a warmer Europa with significant subsurface water, scientists said.
