Hubble Discovers Water Vapor on Exoplanet GJ 9827d: A Potential Water World?
September 15, 2025
NASA's Hubble telescope detects water vapor in the atmosphere of exoplanet GJ 9827d, sparking new questions about the nature of these water-rich worlds.
In a landmark discovery, NASA's Hubble Space Telescope has detected water vapor in the atmosphere of GJ 9827d, a small exoplanet located just 97 light-years away in the constellation Pisces. This planet, approximately twice the diameter of Earth, is now the smallest exoplanet where atmospheric water vapor has been confirmed, opening a new chapter in our search for worlds beyond our solar system.
A Steamy Atmosphere: What Did Hubble Find?
Scientists used Hubble's spectrographic capabilities to analyze the starlight filtering through GJ 9827d's atmosphere as it transited its host star over three years. The data revealed the unmistakable signature of water molecules. This finding is a critical step forward, demonstrating that even smaller, Earth-sized planets can be candidates for atmospheric study with current and future telescopes like the James Webb Space Telescope (JWST).
A Water World or a Mini-Neptune?
The discovery raises an intriguing question: what kind of world is GJ 9827d? Two primary scenarios are being considered. It could be a 'mini-Neptune' with a hydrogen-rich atmosphere containing water, or it might be a warmer version of Jupiter's moon Europa—a true water world with a steamy, water-dominated atmosphere blanketing a rocky core. Distinguishing between these possibilities will be a key task for future observations.
Observing water on a planet this small is a groundbreaking milestone. It pushes us closer than ever to characterizing potentially habitable worlds, even if this specific one isn't.
Too Hot to Handle
Don't pack your bags just yet. With a surface temperature searing at 800 degrees Fahrenheit (425 degrees Celsius), GJ 9827d is as hot as Venus. This intense heat means any water would exist as a superheated steam, making it inhospitable for life as we know it. This heat likely boiled off any primordial hydrogen and helium from its atmosphere, leaving behind the heavier water molecules Hubble was able to detect.
- Planet Type: Super-Earth / Mini-Neptune
- Distance: 97 light-years from Earth
- Diameter: Approximately 2x that of Earth
- Key Discovery: Confirmed water vapor in its atmosphere
- Surface Temperature: ~800°F (425°C)
While GJ 9827d itself is not a candidate for life, it serves as a crucial natural laboratory. Future analysis by the JWST could pinpoint the exact atmospheric composition, helping scientists understand the formation and evolution of water-rich planets across the galaxy.
Hubble Discovers Water Vapor on Exoplanet GJ 9827d: A Potential Water World? - FAQs
GJ 9827d is an exoplanet about twice Earth's diameter, located 97 light-years away, where the Hubble Space Telescope has detected atmospheric water vapor.
No. The planet's scorching temperature of 800°F (425°C) makes it far too hot for liquid water and thus inhospitable for life as we know it.
Hubble observed the planet as it passed in front of its star. By analyzing the starlight that filtered through the planet's atmosphere, scientists identified the unique signature of water molecules.
It is the smallest exoplanet to date where water vapor has been detected, providing a crucial target for the James Webb Space Telescope to study the formation of water-rich worlds.