Haze on ‘hot Jupiters’ hides atmospheric water, study finds

Hot Jupiters are Jupiter-sized planets that orbit very close to their host star, and we’ve discovered some of these planets have water in their atmospheres, while others have none.

According to a new study in the Astrophysical Journal, NASA researchers have found that a layer of haze could be preventing us from seeing water in the atmospheres of some hot Jupiters.

Using Hubble to examine hot Jupiters

To reach their conclusion, the study team examined a collection of hot Jupiters discovered with the Hubble Space Telescope.

“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,” Aishwarya Iyer, a graduate student at California State University, Northridge, said in a NASA press release.

The scientists learned that the atmospheres of approximately one half the planets in the study were obstructed by clouds or haze. The clouds are probably not made of water, the study said, because the planets in this collection are too hot for water clouds to persist.

“Clouds or haze seem to be on almost every planet we studied,” Iyer noted. “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.”

The researchers examined a set of 19 hot Jupiters detected by Hubble. The telescope’s Wide Field Camera 3 had found water vapor in the atmospheres of 10 of the 19 planets. However, that data was spread across over a dozen research studies. The procedures of examining and interpretation varied across these studies as the analyses were executed separately. There had not been one overarching investigation of all these planets, the researchers said.

For the study, the researchers first had to standardize the information across all the previous studies. They blended the datasets for all 19 hot Jupiters to produce an average overall light spectrum for the group of planets. They then evaluated this information to simulate clear, cloud-free atmospheres and those with assorted cloud thicknesses.

The researchers established that, for nearly every planet they studied, haze or clouds were blocking an average of half of the atmosphere.

“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.

The study team said they do not know what these clouds are made of and what they might look like.

Study author Robert Zellem, a postdoctoral fellow at NASA, said the results of his team’s work have implications for future research on planet formation.

“Clouds or haze being on almost all these planets is pretty surprising,” Zellem said.”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.”

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Image credit: NASA

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