Exoplanets’ water hidden by clouds?

Astronomers have found many hot Jupiters with water in their atmospheres, but others appear to have none. Scientists at NASA’s Jet Propulsion Laboratory, Pasadena, 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. Aishwarya Iyer, a JPL intern and master’s degree candidate at California State University, Northridge, who led the study, said:

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.

The new study, published in the June 1, 2016 issue of the Astrophysical Journal, 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. Iyer said:

Clouds or haze seem to be on almost every planet we studied. 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.

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 vapor 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 analyzing and interpretation varied because the studies were conducted separately. There had not been one overarching analysis of all these planets.