The James Webb Space Telescope (JWST) has made an exciting discovery – it has detected water vapour around a rocky exoplanet located 26 light-years away from Earth. This marks the first time that scientists have marked the existence of water vapour in the environment of a rocky exoplanet.
The exoplanet, named GJ 486 b, orbits a little, cool red dwarf star which is the most familiar kind of star in the universe. Exoplanets found in the “habitable zone” - the perfect distance from a star that allows the planet to be warm enough to host liquid water on its surface - typically orbit red dwarfs very closely as they are not as warm as the Sun.
Scientists have previously questioned whether rocky planets orbiting red dwarf stars can maintain or regain atmospheres due to the ultraviolet and X-ray radiation that the stars emit. This radiation has the potential to demolish fragile layers of gas.
GJ 486 b is a hot, rocky exoplanet that is approximately 30% larger than Earth with much stronger surface gravity than our planet. It is so close to the host star that it completes one orbit every 1.5 Earth days, and this proximity heats the planet to a surface temperature of 800 degrees Fahrenheit (430 degrees Celsius). It is also believed that the planet is tidally locked, which means that one side always faces the star while the other is a permanent night side.
Although GJ 486 b is too hot to be habitable, the water vapour detected by the JWST’s Near-Infrared Spectrograph indicates that the planet may have an atmosphere, despite its heat and proximity to the star.
Detecting water vapour in an atmosphere around a rocky exoplanet would be a significant breakthrough for exoplanet science, as it would make the planet similar in a way to planets in our solar system like Earth and Mars. However, the astronomers observing GJ 486 b are cautious with their interpretation of the findings, as it is possible that the water vapour is connected to the star itself.
“We see a signal, and it’s almost certainly due to water. But we can’t tell yet if that water is part of the planet’s atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star,” said lead study author Sarah Moran, postdoctoral research associate at the University of Arizona in Tucson.
The red dwarf star hosting GJ 486 b is much smaller and cooler than the Sun, which means it may contain even more water vapour in its starspots – areas that appear dark on stars because they’re cooler than other parts of the surface. This could create a signal that could be misinterpreted as a planetary atmosphere surrounding the closely orbiting exoplanet.
Future observations of GJ 486 b using different instruments on the JWST could reveal additional details about the source of the water vapour. If the exoplanet does indeed have an atmosphere, it would need replenishment from a constant source, like steam from volcanoes, as the heat and radiation from the star would likely erode the atmosphere over time.
In conclusion, the detection of water vapour around a rocky exoplanet marks a significant milestone in exoplanet science, but scientists must proceed with caution and continue to analyze the data captured by the JWST’s instruments to determine the source of the water vapour.