Clouds or haze layers in the atmosphere of 'hot Jupiters' could be preventing a substantial amount of water from being detected by space telescopes, a new study led by an Indian-origin researcher has found.
Water is a hot topic in the study of exoplanets, including "hot Jupiters," whose masses are similar to that of Jupiter, but which are much closer to their parent star than Jupiter is to the Sun.
They can reach a scorching 1,100 degrees Celsius, meaning any water they host would take the form of water vapour.
Astronomers have found many hot Jupiters with water in their atmospheres, but others appear to have none.
Scientists at NASA's Jet Propulsion Laboratory (JPL) in California wanted to find out what the atmospheres of these giant worlds have in common.
Researchers focused on a collection of hot Jupiters studied by NASA's Hubble Space Telescope. They found that the atmospheres of about half of the planets were blocked by clouds or haze.
"The motivation of our study was to see what these planets would be like if they were grouped together, and to see whether they share any atmospheric properties," said Aishwarya Iyer, a JPL intern and master's degree candidate at California State University, who led the study.
The study suggests that clouds or haze layers could be preventing a substantial amount of atmospheric water from being detected by space telescopes.
The clouds themselves are likely not made of water, as the planets in this sample are too hot for water-based clouds.
"Clouds or haze seem to be on almost every planet we studied," Iyer said.
"You have to be careful to take clouds or haze into account, or else you could underestimate the amount of water in an exoplanet's atmosphere by a factor of two," said Iyer.
In the study, scientists looked at a set of 19 hot Jupiters previously observed by Hubble. The telescope's Wide Field Camera 3 had detected water vapour in the atmospheres of 10 of these planets, and no water on the other nine.
But that information was spread across more than a dozen studies. The methods of analysing and interpretation varied because the studies were conducted separately. There had not been one overarching analysis of all these planets.
Researchers combined the datasets for all 19 hot Jupiters to create an average overall light spectrum for the group of planets.
They then compared these data to models of clear, cloud-free atmospheres and those with various cloud thicknesses.
The scientists determined that, for almost every planet they studied, haze or clouds were blocking half of the atmosphere, on average.
"In some of these planets, you can see water peeking its head up above the clouds or haze, and there could still be more water below," Iyer said.
The study was published in the Astrophysical Journal.
