Free Astronomy Magazine May-June 2018

30 MAY-JUNE 2018 SPACE CHRONICLES WASP-39b : a lot of water in its atmosphere by NASA/ESA S cientists used NASA’s Hubble and Spitzer space telescopes to find a large amount of water in the atmosphere of WASP- 39b, a hot, bloated, Sat- urn-mass exoplanet that resides about 700 light- years from Earth. This “hot Saturn” actually has three times as much water as Saturn does. WASP-39b whips around a quiet, Sun- like star, called WASP-39, once every four days. The exoplanet is currently po- sitioned more than 20 times closer to its star than Earth is to the Sun. It is tidally locked, meaning it always shows the same face to its star. [NASA, ESA, and G. Bacon (STScI)] M uch like detectives study fingerprints to identify the culprit, scientists used NASA’s Hubble and Spitzer space telescopes to identify the “finger- prints” of water in the atmosphere of a hot, bloated, Saturn-mass exo- planet some 700 light-years away. And, they found a lot of water. In fact, the planet, known as WASP- 39b, has three times as much water as Saturn does. Though no planet like this resides in our solar system, WASP-39b can pro- vide new insights into how and where planets form around a star, say researchers. This exoplanet is so unique, it underscores the fact that the more astronomers learn about the complexity of other worlds, the more there is to learn about their origins. This latest observation is a significant step toward characteriz- ing these worlds. Although the researchers predicted they’d see water, they were sur- prised by how much water they found in this “hot Saturn.” Because WASP-39b has so much more water than our famously ringed neighbor, it must have formed differently. The amount of water suggests that the planet actually developed far away from the star, where it was bombarded by a lot of icy material. WASP-39b likely had an interesting evolutionary history as it migrated in, taking an epic journey across its planetary system and perhaps oblit- erating planetary objects in its path. “We need to look outward so we can understand our own solar sys- U sing 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 re- searchers 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. [NASA, ESA, G. Bacon and A. Feild (STScI), and H. Wakeford (STScI/Univ. of Exeter)]