Astronomers using NASA's Hubble Space Telescope say they've found faint signatures of water in the atmospheres of five distant planets.

Although the probable existence of atmospheric water has been detected previously on a few exoplanets orbiting stars beyond our solar system, the new study is the first to conclusively measure and compare the profiles and intensities of these signatures on multiple worlds, NASA reported Tuesday.

"We're very confident that we see a water signature for multiple planets," Avi Mandell, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., said. "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."

The five planets studied are hot Jupiters, massive worlds that orbit close to their host stars.

"To actually detect the atmosphere of an exoplanet is extraordinarily difficult," study researcher L. Drake Deming of the University of Maryland said. "But we were able to pull out a very clear signal, and it is water."