Free Astronomy Magazine July-August 2016

SPACE CHRONICLES Cloudy days on exoplanets may hide atmospheric water W ater is a hot topic in the study of exoplanets, in- cluding “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 scorch- ing 2,000 degrees Fahrenheit (1,100 degrees Celsius), meaning any wa- ter they host would take the form of water vapor. 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 block- ed by clouds or haze. “The motiva- tion of our study was to see what these planets would be like if they were grouped together, and to see whether they share any atmospher- ic properties,” said Aishwarya Iyer, a JPL intern and master's degree candidate at California State Uni- versity, Northridge, who led the study. The new study, published in the June 1 issue of the Astrophysical Journal, suggests that clouds or by NASA H ot Jupiters, exo- planets around the same size as Jupiter that orbit very closely to their stars, often have clouds or haze lay- ers in their atmo- spheres. This may pre- vent space telescopes from detecting atmo- spheric water that lies beneath the clouds, ac- cording to a study in the Astrophysical Jour- nal. [NASA/JPL-Caltech] haze layers could be preventing a substan- tial amount of atmo- spheric 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 ac- count, or else you could underestimate the amount of water in an exoplanet's atmosphe- re by a factor of two.” In the study, scientists