Free Astronomy Magazine March-April 2024

46 MARCH-APRIL 2024 exist around other stars,” said team member Björn Benneke of the Uni- versité de Montréal. “This is an im- portant step toward determining the prevalence and diversity of at- mospheres on rocky planets.” However, it remains too early to tell whether Hubble spectroscopically measured a small amount of water vapour in a puffy hydrogen-rich at- mosphere, or if the planet’s atmos- phere is mostly made of water, left behind after a primaeval hydrogen/ helium atmosphere evapourated un- der stellar radiation. “Our observing programme was de- signed specifically with the goal of not only detecting the molecules in the planet’s atmosphere, but of ac- tually looking specifically for water vapour. Either result would be ex- citing, whether water vapour is dominant or just a tiny species in a hydrogen-dominant atmosphere,” said the science paper’s lead author, Pierre-Alexis Roy of the Université de Montréal. “Until now, we had not been able to directly detect the atmosphere of such a small planet. And we’re slowly getting into this regime now,” added Benneke. “At by NASA/ESA − Bethany Downer A stronomers using the NASA/ ESA Hubble Space Telescope observed the smallest exo- planet where water vapour has been detected in its atmosphere. At only approximately twice Earth’s di- ameter, the planet GJ 9827d could Water vapour in small exoplanet’s atmosphere be an example of potential planets with water-rich atmospheres else- where in our galaxy. “This would be the first time that we can directly show through an atmospheric de- tection that these planets with water-rich atmospheres can actually