Hot Jupiters, exoplanets around the same size as Jupiter that orbit very closely to their stars, often have cloud or haze layers in their atmospheres. This may prevent space telescopes from detecting atmospheric water that lies beneath the clouds, according to a study in the Astrophysical Journal. Credit: NASA/JPL-Caltech
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 2,000F, meaning any water 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 JPL, Pasadena, CA , wanted to find out what the atmospheres of these giant worlds have in common.
They found that the atmospheres of about half of the planets studied by Hubble were blocked by clouds or haze suggesting 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. “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.”
They 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. 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 spectrum for the group of planets. They then compared these data to models of clear, cloud-free atmospheres and those with various cloud thicknesses.
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. Scientists do not yet know the nature of these clouds or hazes, including what they are they made of.
The new research could have implications for follow-up studies eg with James Webb Space Telescope. Exoplanets with thick cloud covers blocking the detection of water and other substances may be less desirable targets for more extensive study. These results are also important for figuring out how planets form. “Did these planets form in their current positions or migrate toward their host stars from farther out? http://www.jpl.nasa.gov/news/news.php?release=2016-144
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