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NASA telescopes discover water-rich exoplanet atmosphere

An artist's depiction of WASP-39b and its parent star. They are located some 700 light-years from Earth. Image Credit: NASA / ESA / G. Bacon and A. Feild / H. Wakeford

An artist’s depiction of WASP-39b and its parent star. They are located some 700 light-years from Earth. Image Credit: NASA / ESA / G. Bacon and A. Feild / H. Wakeford

Scientists using NASA’s Hubble and Spitzer space telescopes in concert have examined the elemental composition of a distant exoplanet’s atmosphere in the highest detail yet. The planet, designated WASP-39b, is about the same mass as Saturn, but has three times as much water, according to NASA.

The WASP-39 system is about 700 light-years away in the direction of the constellation Virgo. So far, WASP-39b is the only planet that has been detected orbiting this sunlike yellow dwarf star. It was discovered in 2011 as part of the Wide Angle Search for Planets (WASP) project when it was observed transiting in front of its parent star.

Using Hubble and Spitzer, astronomers analyzed the atmosphere of the "hot Saturn" exoplanet WASP-39b, and they captured the most complete spectrum of an exoplanet's atmosphere possible with present-day technology. By dissecting starlight filtering through the planet's atmosphere into its component colors, the team found clear evidence for water vapor. Although the researchers predicted they would see water, they were surprised by how much water they found - three times as much water as Saturn has. This suggests that the planet formed farther out from the star, where it was bombarded by icy material. Image and Caption Credit: NASA / ESA / G. Bacon and A. Feild / H. Wakeford

(Click to enlarge) Using Hubble and Spitzer, astronomers analyzed the atmosphere of the “hot Saturn” exoplanet WASP-39b, and they captured the most complete spectrum of an exoplanet’s atmosphere possible with present-day technology. By dissecting starlight filtering through the planet’s atmosphere into its component colors, the team found clear evidence for water vapor. Although the researchers predicted they would see water, they were surprised by how much water they found – three times as much water as Saturn has. This suggests that the planet formed farther out from the star, where it was bombarded by icy material. Image and Caption Credit: NASA / ESA / G. Bacon and A. Feild / H. Wakeford

While the mass of WASP-39b is only about 28 percent that of Jupiter’s, its radius is roughly 27 percent greater than the Solar System’s largest planet. For comparison, Saturn’s mass and radius is 29 percent and 83 percent of Jupiter’s, respectively.

The exoplanet, however, isn’t known to have any rings, NASA said. Moreover, while Saturn, orbits the Sun once every 29 years (nearly 11,000 days), WASP-39b circles its star every four days.

Because of its close proximity to its star, WASP-39b is tidally locked. As such, this “hot Saturn” has a dayside temperature of 1,430 degrees Fahrenheit (776.7 degrees Celsius), according to NASA, with powerful winds transporting heat from the dayside to the permanent nightside, keeping it almost as hot.

Scientists used the Hubble Space Telescope and Spitzer Space Telescope to examine starlight as WASP-39b passed in between the distant star and Earth, allowing them to observe the way certain bands of light were filtered out by the planet’s atmosphere. According to NASA, the team led by Hannah Wakeford of the Space Telescope Science Institute in Baltimore and the University of Exeter in Devon, United Kingdom, captured the most complete spectrum of an exoplanet’s atmosphere possible with present-day technology.

“This spectrum is thus far the most beautiful example we have of what a clear exoplanet atmosphere looks like,” Wakeford said in a NASA news release.

Scientists were able to determine that the upper atmosphere of the planet was fairly clear, as opposed to being cloudy or hazy. If the upper atmosphere was thick with clouds or haze, the starlight would have been blocked on more bands than were detected. 

NASA said Wakeford and her team were also also able to determine the approximate quantity of water in WASP-39b’s atmosphere could be as high as three times the amount in Saturn’s. To quantify how much that is, one paper published in The Astrophysical Journal estimated the total amount of water in the ringed world’s atmosphere was about 15 to 16 times the mass of Earth.

In a paper published in The Astrophysical Journal’s January 2018 edition and titled “The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint,” Wakeford and her team speculated that the high concentration of water and heavy elements might be explained if formation of the planet occurred in the outer part of its system. Then, over the course of its life, it may have migrated inward, absorbing other planetary bodies in its path.

According to NASA, Wakeford hopes to use the James Webb Space Telescope after it launches in 2019 to produce an even more complete spectrum of WASP-39b. 

“WASP-39b shows exoplanets can have much different compositions than those of our Solar System,” said the paper’s co-author, David Sing of the University of Exeter in Devon, United Kingdom. “Hopefully this diversity we see in exoplanets will give us clues in figuring out all the different ways a planet can form and evolve.”

 

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Christopher Paul has had a lifelong interest in spaceflight. He began writing about his interest in the Florida Tech Crimson. His primary areas of interest are in historical space systems and present and past planetary exploration missions. He lives in Kissimmee, Florida, and also enjoys cooking and photography. Paul saw his first Space Shuttle launch in 2005 when he moved to central Florida to attend classes at the Florida Institute of Technology, studying space science, and has closely followed the space program since. Paul is especially interested in the renewed effort to land crewed missions on the Moon and to establish a permanent human presence there. He has covered several launches from NASA's Kennedy Space Center and Cape Canaveral for space blogs before joining SpaceFlight Insider in mid-2017.

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