Many "hot Jupiters" — exoplanets with masses similar to that of Jupiter — have been detected with atmospheric water, but others appear to be without it. How come?

Hot Jupiters, which can reach a sweltering temperature of 1,100 degrees Celsius (2,000 degrees Fahrenheit), are closer to their parent stars than Jupiter is to the sun.

Because of the scorching heat, any water that these exoplanets possess will transform into water vapor.

In order to find out why some exoplanets seem to lack water vapor, scientists from NASA's Jet Propulsion Laboratory embarked on a study to compare the atmospheres of several exoplanets. Their findings could prove to be groundbreaking or not at all.

Investigating Exoplanets

JPL scientists examined a set of 19 hot Jupiters that were previously observed by the Hubble Space Telescope. Hubble's Wide Field Camera 3 detected atmospheric water vapor in 10 of 19 exoplanets, while there was no water detected on the remaining nine.

However, Hubble's data were spread across more than nine studies, which were conducted separately. The method of interpretation and analysis varied significantly, so there was no conclusive analysis of all the exoplanets.

The JPL team decided to even out the data in order to better compare the exoplanets and look for a pattern. They combined sets of data for all 19 exoplanets to produce a standard light spectrum for the group.

The datasets were then compared to scientific models of cloud-free atmospheres and planets with several thicknesses of clouds.

Implications Of The Study

For every planet that the researchers studied, they found that clouds or haze were blocking 50 percent of the atmosphere.

JPL Intern Aishwarya Iyer of California State University, Northridge says in some of the planets, there is water "peeking" up above the clouds.

"There could still be more water below," says Iyer.

Indeed, the findings suggest that clouds or haze could be preventing a considerable amount of water vapor from being spotted by space telescopes.

Robert Zellem, a co-author of the study, says it is surprising that there are clouds or haze on almost all the planets.

Scientists have yet to identify the real nature of the clouds, but they do know that the clouds are not made of water. Exoplanets are simply too hot for water-based clouds to form.

Iyer says scientists have to be cautious in taking into account the presence of clouds or haze because they could underestimate the amount of atmospheric water.

The new study, which is published in the Astrophysical Journal, is important, as it could help scientists figure out how exoplanets form. The findings corroborate the study published in December last year, which explained that there might be undetected water under the clouds or haze found among hot Jupiters.