WASHINGTON, Dec. 3 (Xinhua) -- Faint signatures of water have been spotted in the atmospheres of five distant planets, U.S. space agency NASA said Tuesday.
The planets are not the size of Earth, but rather massive worlds known as hot Jupiters because they orbit so close to their stars, NASA said in a statement.
The presence of atmospheric water was reported previously on a few exoplanets orbiting stars beyond our solar system, but researchers led by the University of Maryland in College Park was for the first time able to conclusively measure and compare the profiles and intensities of these signatures on multiple worlds, it said.
"We're very confident that we see a water signature for multiple planets," said Avi Mandell, a planetary scientist at NASA 's Goddard Space Flight Center, and lead author of an Astrophysical Journal paper. "This work really opens the door for comparing how much water is present in atmospheres on different kinds of exoplanets, for example hotter versus cooler ones."
All the five planets, named WASP-17b, HD209458b, WASP-12b, WASP- 19b and XO-1b, orbit nearby stars, however, the strengths of their water signatures varied, the U.S. space agency said.
WASP-17b, a planet with an especially puffed-up atmosphere, and HD209458b had the strongest signals. The signatures for the other three planets, WASP-12b, WASP-19b and XO-1b, also are consistent with water, it said.
The researchers used Hubble Space Telescope's Wide Field Camera 3 to explore the details of absorption of light through the planets' atmospheres. The observations were made in a range of infrared wavelengths where the water signature, if present, would appear. They compared the shapes and intensities of the absorption profiles, and the consistency of the signatures gave them confidence they saw water.
The researchers were surprised that the water signals were all less pronounced than expected, and they suspect this is because a layer of haze or dust blankets each of the five planets. This haze can reduce the intensity of all signals from the atmosphere in the same way fog can make colors in a photograph appear muted.
At the same time, haze alters the profiles of water signals and other important molecules in a distinctive way, NASA added.