Two teams of scientists have found faint but clear signatures of water in the atmospheres of five distant exoplanets. Although atmospheric water has been detected before on a few distant planets, these studies are the first to conclusively determine its presence.
Using NASA’s powerful Hubble Space Telescope, the scientists were able for the first time to measure and compare the chemical profiles and intensities of water signatures on multiple worlds.
“To actually detect the atmosphere of an exoplanet is extraordinarily difficult,” Prof. L. Drake Deming, an astronomer at the University of Maryland, said in a statement. “But we were able to pull out a very clear signal, and it is water.”
Deming, an expert at using data from space and ground-based telescopes, led a census of exoplanet atmospheres that produced the new findings. Deming and colleagues described two of the five planets in a study published Sept. 10 in the Astrophysical Journal.
Avi Mandel, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of a paper reporting on the three other exoplanets, said his team was “confident that we see a water signature for multiple planets.” Mandel’s study was published today (Dec. 3) in the Astrophysical Journal.
“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,” Mandel added.
In both studies, astronomers used Hubble’s Wide Field Camera 3 to study how light was absorbed through the planets’ atmospheres. The observations were made in a range of infrared wavelengths where a signature pattern appears when water is present. When the teams compared the shapes and intensities of absorption profiles, the consistency of the signatures made them confident they were seeing water.
The five planets–WASP-17b, HD209458b, WASP-12b, WASP-19b, and XO-1b–are massive hot Jupiters that orbit close to their host stars. The strengths of the water signals coming from the planets varied, with WASP-17b and HD209458b being the strongest.
The scientists were surprised by how hazy all five exoplanets appeared. But both Mandel and Deming pointed out that other researchers are finding evidence of haze around exoplanets.
“These studies, combined with other Hubble observations, are showing us that there are a surprisingly large number of systems for which the signal of water is either attenuated or completely absent,” said Deming’s co-author Heather Knutsen of the California Institute of Technology. “This suggests that cloudy or hazy atmospheres may in fact be rather common for hot Jupiters.”