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Cloudy with a Chance of Sand.

THE PROBLEM: Clouds in the atmospheres of extremely large and warm exoplanets--known as "hot Jupiters"--can hinder measurements of gases that could help scientists understand how these planets formed. "We have found a lot of clouds: some kinds of particles--not molecules, but small droplets--that are hanging out in these atmospheres," explains Peter Gao of the University of California, Berkeley. "We don't really know what they are made of, but they are contaminating our observations, essentially making it more difficult for us to assess the composition and abundances of important molecules, like water and methane."

THE SOLUTION: Gao and colleagues developed a model that predicts what kind of clouds can be found on these exoplanets. The model was originally used for Earth's clouds, but now has been extended to environments with much higher temperatures--up to 2,500[degrees]C (4,600[degrees]F)--such as found on hot Jupiters, and indicates which elements could form clouds in such conditions. "The idea is that the same physical principles guide the formation of all types of clouds," says Gao.

While scientists have theorized a variety of possible components of these clouds--from molten salt to aluminum oxides--the model showed that silicates are the most common clouds in the exoplanet atmospheres--at a temperature range of about 600[degrees]-1,700[degrees]C. "The dominant cloud species is as common as sand--it is essentially sand," says the University of Bristol's Hannah Wakeford, a coauthor on the paper.

On some cooler exoplanets, long hydrocarbon chains can create a high-level haze similar to smog.

The model also pinpointed the temperature ranges of planets with the least amount of cloud cover--and therefore best viewing of atmospheric gases: between about 600[degrees] and 1,100[degrees]C, and more than 1,900[degrees]C.

The research was published in Nature Astronomy. [Source: University of California, Berkeley]

Caption: Predicted cloud altitudes and compositions for a range of temperatures common on hot Jupiter planets. The range, in Kelvin, corresponds to about 800-3,500[degrees]F or 427-1,927[degrees]C. [Credit: University of California, Berkeley image by Peter Gao]

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Title Annotation:NOWCAST: PARCELS
Publication:Bulletin of the American Meteorological Society
Geographic Code:1USA
Date:Sep 1, 2020
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