Exoplanets' Missing Water Mystery Solved

A team of astronomers have used NASA/ESA's Hubble and Spitzer Space Telescopes to study the atmosphere on ten extremely hot, Jupiter-sized exoplanets, according to a study. This is the largest number of such planets that has ever been studied, and interestingly, some of these exoplanets had less water than what the researchers had originally expected.

Astronomers have discovered almost 2,000 planets that orbit other stars. Many of these planets are referred to as "hot Jupiters," due to their hot and gaseous features, which are almost identical to Jupiter's atmosphere. Their surfaces are hot since they orbit quite close to their stars.

In previous observations, only three of these exoplanets were studied in detail. The astronomers used Hubble and Spitzer to study and compare the temperatures, mass and sizes of the ten exoplanets.

"I'm really excited to finally 'see' this wide group of planets together, as this is the first time we've had sufficient wavelength coverage to be able to compare multiple features from one planet to another," David Sing, lead author of the study the University of Exeter, said in a news release. "We found the planetary atmospheres to be much more diverse than we expected."

When an exoplanet passes in front of its host star, some of the starlight travels through the planet's outer atmosphere, which leaves a unique fingerprint on the starlight. These fingerprints enabled the researchers to extract varying elements, including water, so that they can differentiate cloudy and cloud-free exoplanets, which could solve the missing water mystery.

The models revealed that cloud-free exoplanets show strong signs of water and the atmospheres of hot Jupiters with faint water signals contain clouds and haze, which tends to hide water from view.  

"The alternative to this is that planets form in an environment deprived of water - but this would require us to completely rethink our current theories of how planets are born," said Jonathan Fortney, coauthor of the study. "Our results have ruled out the dry scenario, and strongly suggest that it's simply clouds hiding the water from prying eyes."

The findings of this study were published in Nature.

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