Scientists using the James Webb Space Telescope (JWST) have discovered the first clear evidence of a “steam world”—a planet surrounded by a steamy, water-rich atmosphere—approximately 100 light-years from Earth, in the constellation Pisces. This discovery expands the catalog of over 5,700 confirmed exoplanets, now including this unique type of water-rich world.
The exoplanet, named GJ 9827 d, is about twice the size of Earth and features an atmosphere predominantly composed of water vapor. Such worlds had only been theorized until now. “It was a very surreal moment,” remarked Eshan Raul, a contributor to the research from the University of Michigan, highlighting the significance of finding a water-rich planet beyond Earth.
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GJ 9827 d is thought to have a thick atmosphere filled with water vapor, and its surface likely lacks ice or flowing water. Researchers compare it to what the icy moons of Jupiter, like Europa, might look like if they orbited closer to the sun. The exoplanet experiences extreme heat, with an estimated surface temperature of 660 degrees Fahrenheit, far hotter than Earth’s average of 59 degrees.
The study, led by Caroline Piaulet-Ghorayeb of the University of Montréal, marks a milestone in the search for atmospheres rich in heavier elements rather than hydrogen. Using JWST’s transmission spectroscopy, researchers analyzed how starlight passes through GJ 9827 d’s atmosphere during its transit, revealing the water vapor signature and providing a deeper understanding of this intriguing “steam world.”
