Free Astronomy Magazine July-August 2016

SPACE CHRONICLES 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 atmo- spheres 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 inter- pretation varied because the studies were conducted separately. There had not been one overarching anal- ysis of all these planets. To compare the planets and look for patterns, the JPL team had to standardize the data. Researchers combined the datasets for all 19 hot Jupiters to create an average overall light spec- trum for the group of planets. They then compared these data to mod- els of clear, cloud-free atmospheres and those with various cloud thick- nesses. The scientists determined that, for almost every planet they studied, haze or clouds were block- ing half of the atmosphere, on aver- age. “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. Scientists do not yet know the na- ture of these clouds or hazes, includ- ing what they are they made of. “Clouds or haze being on almost all these planets is pretty surprising,” said Robert Zellem, a postdoctoral fellow at JPL and co-author of the study. The implications of this result agree with findings published in the Dec. 14, 2015, issue of the journal Na- ture. The Nature study used data from NASA's Hubble and Spitzer Space Telescopes to suggest that clouds or haze could be hiding un- detected water in hot Jupiters. This new study uses exoplanet data from a single instrument on Hubble to uniformly characterize a larger group of hot Jupiters, and is the first to quantify how much of the atmo- sphere would be shielded as a result of clouds or haze. The new research could have impli- cations for follow-up studies with future space observatories, such as NASA's James Webb Space Tele- scope. Exoplanets with thick cloud covers blocking the detection of water and other substances may be less desirable targets for more ex- tensive study. These results are also important for figuring out how planets form, scientists say. “Did these planets form in their current positions or migrate toward their host stars from farther out? Understanding the abundances of molecules such as water helps us answer those questions,” Zellem said. “This study is an exciting step forward for the study of exoplanets and comparing their properties,” said Mark Swain, study co-author and group supervi- sor for the exoplanet discovery and science group at JPL. n