Astronomers using the NASA/ESA Hubble Space Telescope have made a groundbreaking discovery, observing water vapor in the atmosphere of the smallest exoplanet ever detected with such a feature. The planet, named GJ 9827d, is approximately twice the size of Earth and orbits a red dwarf star located 97 light-years away in the constellation Pisces.

GJ 9827d was initially discovered by NASA’s Kepler Space Telescope in 2017 and completes an orbit around its host star every 6.2 days. This finding raises the possibility of the existence of other planets with water-rich atmospheres within our galaxy, marking a significant step in understanding the prevalence and diversity of atmospheres on rocky planets.

The study, published in The Astrophysical Journal Letters, highlights the importance of this discovery. However, it is still too early to determine whether the detected water vapor signifies a predominantly hydrogen-rich atmosphere with a small amount of water vapor, or if the planet’s atmosphere is primarily composed of water, possibly leftover from a previous hydrogen/helium atmosphere that evaporated under stellar radiation.

Pierre-Alexis Roy, the lead author of the study, emphasized the significance of the findings. He expressed excitement about the potential implications, regardless of whether water vapor dominates the atmosphere or exists as a minor component within a hydrogen-rich environment.

Given the planet’s scorching temperature of approximately 425°C, it would likely be an inhospitable, steamy world if the atmosphere were predominantly composed of water vapor. The team is currently considering two possibilities: the planet may retain a hydrogen-rich envelope with traces of water, resembling a mini-Neptune, or it could resemble a warmer version of Jupiter’s moon Europa, which harbors twice as much water as Earth beneath its icy surface.

These findings mark a significant milestone in the study of exoplanet atmospheres, providing valuable insights into the potential habitability and composition of distant worlds. As technology advances, astronomers anticipate further discoveries that will enhance our understanding of the universe and the possibility of finding Earth-like planets beyond our solar system.