Hubble Detects Water Vapor on Steamy Super-Earth Exoplanet GJ 9827d
September 8, 2025
NASA's Hubble Telescope has detected water vapor in the atmosphere of GJ 9827d, a super-Earth exoplanet, raising key questions about its formation and composition.
In a groundbreaking discovery, astronomers using NASA's Hubble Space Telescope have detected water vapor in the atmosphere of a small exoplanet designated GJ 9827d. At only about twice Earth's diameter, it is the smallest exoplanet to date where water vapor has been identified, offering a unique opportunity to study worlds beyond our solar system. This finding brings us one step closer to understanding the diverse environments of planets across our galaxy.
What is Super-Earth GJ 9827d?
GJ 9827d orbits a red dwarf star located 97 light-years away in the constellation Pisces. It completes one orbit in a swift 6.2 days, placing it extremely close to its star. This proximity results in scorching surface temperatures estimated at around 800 degrees Fahrenheit (427 degrees Celsius), making it as hot as Venus and inhospitable for life as we know it. The planet was initially discovered by NASA's Kepler Space Telescope in 2017.
- Water-Rich World: One theory suggests GJ 9827d could be a 'mini-Neptune' that lost its primordial hydrogen/helium atmosphere due to stellar radiation, leaving behind a dense, water-vapor-rich atmosphere.
- Rocky World with a Volcanic Past: Alternatively, it could be a warmer version of Jupiter's moon Europa, with a significant water fraction beneath a rocky crust, now shrouded in steam.
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. It’s an important step toward determining the prevalence and diversity of atmospheres on rocky planets.
The detection of water is a critical milestone, but the planet's high temperature rules out habitability. Future observations with the James Webb Space Telescope (JWST) will be essential to search for other molecules and paint a more complete picture of GJ 9827d's atmospheric composition, helping scientists distinguish between a steamy, water-world scenario and one with a puffy hydrogen envelope.
Hubble Detects Water Vapor on Steamy Super-Earth Exoplanet GJ 9827d - FAQs
GJ 9827d is a 'super-Earth' exoplanet, approximately twice the diameter of Earth, orbiting a red dwarf star 97 light-years away. Its surface is extremely hot, around 800°F.
It is the smallest exoplanet to date where water vapor has been detected in the atmosphere. This discovery provides a crucial target for studying the atmospheric composition of smaller, rocky planets.
No, GJ 9827d is not considered habitable. Its surface temperature is about 800 degrees Fahrenheit (427 degrees Celsius), which is far too hot for liquid water to exist on its surface.
Astronomers used the Hubble Space Telescope to observe the planet as it passed in front of its star (a transit) over three years. By analyzing the starlight filtering through the planet's atmosphere, they identified the unmistakable signature of water molecules.