Scientists using the NASA/ESA Hubble Space Telescope have identified water vapour in the atmosphere of a small exoplanet, known as GJ 9827d, thanks to the telescope’s remarkable precision.
Discovered by NASA’s Kepler Space Telescope in 2017, GJ 9827d, roughly twice the size of Earth, has been under Hubble’s observation during 11 transits spanning three years. The rocky planet could serve as an example of other planets with water-rich atmospheres in our galaxy.
The researchers are still working to determine whether water vapour dominates the exoplanet’s atmosphere or if it is just a minor component within a predominantly hydrogen-rich atmosphere.
Given GJ 9827d’s Venus-like temperatures, the researchers believe it would be an unwelcoming and steamy world if water vapour prevails in its atmosphere.
Two potential scenarios are being considered for GJ 9827d. It could either have a hydrogen-rich envelope with traces of water vapour, resembling a mini-Neptune, or it might resemble a warmer version of Jupiter’s moon Europa, which holds twice as much water as Earth beneath its crust.
The researchers present two theories:
If GJ 9827d has a residual water-rich atmosphere, it may have initially formed farther from its host star, where temperatures are very low, and water exists as ice. Over time, the planet could have migrated closer to the star, receiving more radiation, which may have led to the heating and escape of hydrogen from its atmosphere due to weak gravity.
Alternatively, the exoplanet might have formed near the hot star with a trace of water in its atmosphere.
Björn Benneke, a researcher from the Université de Montréal and part of the research team, emphasized the importance of this finding, expressing, “For the first time, we can directly demonstrate through atmospheric detection that planets with water-rich atmospheres can indeed be present around other stars. This marks a crucial milestone in understanding the abundance and variety of atmospheres on rocky planets.”
