Webb Telescope Spots Evidence of a Distant, Water-Rich 'Steam World'

The James Webb Space Telescope has spotted something steamy. No, not that kind of steamy. Using its spectroscopic instruments, the observatory has found evidence that a distant exoplanet’s atmosphere could be chock-full of water in its gaseous state. If Webb is on the right track, its findings will represent the first-ever discovery of a so-called “steam world” outside of the solar system.
In a paper for The Astrophysical Journal Letters, an international team of researchers describes the atmospheric composition of GJ 9827 d, a sub-Neptune exoplanet nearly 100 light-years away from Earth. GJ 9827 d itself isn’t a new discovery; NASA’s Kepler space telescope found it back in 2017. After the agency worked with the European Space Agency (ESA) and the Canadian Space Agency (CSA) to launch Webb, however, NASA unlocked troves of data via Webb’s spectroscopy instruments—namely its Near Infrared Imager and Slitless Spectrograph (NIRISS) and Near Infrared Spectrograph (NIRSpec). 
The researchers’ work on GJ 9827 d began when they detected hints of water vapor in the planet’s atmosphere earlier this year. This encouraged them to examine the spectrum of light that traveled through the GJ 9827 d’s atmosphere as it passed by the orange dwarf star it orbits. The spectroscopy data the team captured enabled them to reverse-engineer the atmospheric conditions that would enable that specific form of light travel to take place. This process, called atmospheric retrieval, revealed that GJ 9827 d’s atmosphere is likely composed almost entirely of water vapor. 
“To be clear, this planet isn’t hospitable to at least the types of life that we’re familiar with on Earth,” said Eshan Raul, a first-year doctoral student of astrophysics at the University of Michigan. Raul’s contribution to the study began when he was an undergraduate student who helped to analyze Webb’s spectroscopy data for GJ 9827 d. “The planet appears to be made mostly of hot water vapor, making it something we’re calling a ‘steam world.”
Astronomers have spent a long time theorizing about the existence of steam worlds, but up until this research into GJ 9827 d, the steamy planets were just that—a theory. Venus might have once been a steam world, but it certainly isn’t one anymore; while scientists have located planets full of ice and moons that could hide subsurface oceans, atmospheres thick with water vapor are more elusive.
“We were searching specifically for water worlds because it was hypothesized that they could exist,” Raul said. “If these are real, it really makes you wonder what else could be out there.”
© 2001-2024 Ziff Davis, LLC., a Ziff Davis company. All Rights Reserved.
ExtremeTech is a federally registered trademark of Ziff Davis, LLC and may not be used by third parties without explicit permission. The display of third-party trademarks and trade names on this site does not necessarily indicate any affiliation or the endorsement of ExtremeTech. If you click an affiliate link and buy a product or service, we may be paid a fee by that merchant.

source