Using data from Hubble and NASA's Spitzer telescopes, astronomers have revealed for the first time the diversity of atmosphere on exoplanets.
An international team of astronomers made the largest ever study of hot Jupiters, exploring and comparing 10 such planets in a bid to understand their atmospheres.
The team was able to discover why some of these worlds seem to have less water than expected -- a long-standing mystery.
To date, astronomers have discovered nearly 2000 planets orbiting other stars. Some of these planets are known as hot Jupiters -- hot, gaseous planets with characteristics similar to those of Jupiter.
They orbit very close to their stars, making their surface hot, and the planets tricky to study in detail without being overwhelmed by bright starlight.
Using the power of both telescopes allowed the team to study the planets, which are of various masses, sizes, and temperatures, across an unprecedented range of wavelengths.
"I am 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," said David Sing from University of Exeter.
"We found the planetary atmospheres to be much more diverse than we expected," he added.
The team's models revealed that while apparently cloud-free exoplanets showed strong signs of water, the atmospheres of those hot Jupiters with faint water signals also contained clouds and haze -- both of which are known 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," explained co-author Jonathan Fortney from University of California.
"Our results have ruled out the dry scenario, and strongly suggest that it's simply clouds hiding the water from prying eyes," he added.
The results were published in the journal Nature.
