Scientists at the Max Planck Institute in Germany used the Hubble Space Telescope to discover that the atmosphere of GJ 9827d, a relatively small planet in another star system, is rich in water vapor. However, it is still too early to celebrate. Its surface is hot enough to melt lead, meaning the world is not suitable for life as we know it. Exoplanet GJ 9827d has a surface temperature comparable to Venus’s temperature of about 400 degrees Celsius, but it’s still an exciting discovery. In fact, this is the smallest discovered exoplanet where water has been discovered. This means scientists are closer than ever to describing a world similar to Earth. GJ 9827d is about twice the size of Earth and orbits the star GJ 9827 in the constellation Pisces, 97 light-years away. The planet is just one of many Earth-like worlds orbiting the approximately 6 billion-year-old star. Hubble observed his GJ 9827d for three years, during which time the planet crossed the star’s disk 11 times. Although its composition was determined using spectral analysis, scientists are still unsure whether water vapor makes up a small portion of the hydrogen-rich atmosphere or, on the contrary, whether the atmosphere is mostly water. Unknown. Over the course of 6 billion years, hydrogen may have evaporated from the atmosphere near its parent star, leaving behind water vapor. This hypothesis is confirmed by the fact that no hydrogen was detected near GJ 9827d. Otherwise, it’s a mini-Neptune, a smaller, hotter version of the solar system’s ice giant with a dense atmosphere made of hydrogen and helium. Alternatively, the planet could resemble a larger, even hotter version of Jupiter’s moon Europa, which is thought to contain twice as much water as Earth beneath its thick icy crust. If GJ 9827d has a water vapor-rich atmosphere, that means the planet was born far from its star where it was cooler, but then moved to its current location. As a result, GJ 9827d was exposed to intense radiation from the star, converting its ice to liquid water and water vapor. Under these conditions, hydrogen heats up and can escape from the atmosphere due to the planet’s relatively low gravity. Perhaps this leak is still occurring. GJ 9827d is currently being studied by the more powerful James Webb Space Telescope (JWST).

source: https://www.mpia.de/news/science/2024-03-gj9827d-water-world