This exoplanet’s ambiance goes full steam forward.
A planet past our photo voltaic system referred to as GJ 9827d has an environment composed virtually utterly of scorching water molecules, astronomers report within the Astrophysical Journal Letters October 4.
“We’re utilizing the time period ‘steam world,’” says astronomer Ryan MacDonald on the College of Michigan in Ann Arbor.
GJ 9827d was found in 2017 orbiting a star about 100 light-years from Earth. At about twice Earth’s measurement and thrice Earth’s mass, it’s a sort of planet referred to as a sub-Neptune (SN: 8/8/22). Worlds like this are the commonest within the galaxy, though our photo voltaic system doesn’t have any.
However simply understanding the planet’s measurement and mass isn’t sufficient to infer what it’s made from. To probe exoplanet skies, astronomers analyze starlight filtering by way of the planet’s ambiance because it passes in entrance of its guardian star (SN: 6/7/24).
MacDonald and colleagues used the James Webb House Telescope to look at two such passes, or transits, of GJ 9827d in November 2023. The Hubble house telescope had made related observations and noticed indicators of water molecules within the planet’s ambiance, astronomers reported final yr. Nevertheless it wasn’t sufficient to inform if the ambiance simply had just a little water in it, or if it was an entire water world.
Combining the 2 telescopes’ views made it unambiguously clear that the ambiance was almost all water. The planet’s temperature is about 340° Celsius, so all of that water needs to be vapor.
Such steam worlds “have been predicted, however that is the primary observational proof that they actually exist,” Macdonald says. “I really feel like a Star Trek explorer.”
There won’t be a stable rocky floor beneath the planet’s steamy skies. Deep within the ambiance, the strain from all that water ought to get excessive sufficient to pressure the water molecules into bizarre and unique types of matter, like supercritical fluids or scorching high-pressure ices, MacDonald says.
That makes GJ 9827d an unlikely place to seek out life. However learning its ambiance is sweet follow for observing planets that is likely to be liveable.
“It’s the proof of precept that we will detect heavier atmospheres,” MacDonald says. “We’re heading in the right direction to the place we need to be, astrobiologically.”
