Using the Wide Field Camera 3 (WFC3) instrument onboard the NASA/ESA Hubble Space Telescope, astronomers have detected water vapor in the transmission spectrum of the sub-Neptune exoplanet Gliese 9827d.
Gliese 9827 is a bright K-type dwarf star some 97 light-years away from Earth in the constellation of Pisces.
Also known as GJ 9827, K2-135 or EPIC 246389858, the star hosts a trio of transiting massive exoplanet, discovered recently by NASA’s Kepler/K2 mission.
The outermost planet, Gliese 9827d (GJ 9827d), completes an orbit around its parent star every 6.2 days and has a radius of 1.96 Earth radii.
Hubble observed this planet during 11 transits — events in which the planet crossed in front of its star — that were spaced out over three years.
During transits, starlight is filtered through the planet’s atmosphere and has the spectral fingerprint of water molecules.
“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,” said Dr. Björn Benneke, an astronomer with the Trottier Institute for Research on Exoplanets at the Université de Montréal.
“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. It pushes closer than ever to characterizing truly Earth-like worlds,” said Dr. Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy.
However, it remains too early to tell whether Hubble spectroscopically measured a small amount of water vapor in a puffy hydrogen-rich atmosphere, or if the planet’s atmosphere is mostly made of water, left behind after a primeval hydrogen/helium atmosphere evaporated under stellar radiation.
“Our observing program was designed specifically with the goal to not only detect the molecules in the planet’s atmosphere, but to actually look specifically for water…
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