Free Astronomy Magazine July-August 2018

31 amount of an element present in the atmosphere, the easier the detection becomes. “The strong signal from helium we measured demonstrates a new technique to study up- per layers of exoplanet atmospheres in a wider range of planets,” said Spake. “Cur- rent methods, which use ultraviolet light, are limited to the closest exoplan- ets. We know there is helium in the Earth’s upper atmosphere and this new technique may help us to detect atmospheres around Earth-sized exoplanets — which is very diffi- cult with current technology.” WASP-107b is one of the lowest density planets known: While the planet is about the same size as Jupiter, it has only 12 percent of Jupiter’s mass. The exoplanet is about 200 light-years from Earth and takes less than six days to orbit its host star. The amount of helium detected in the atmosphere of WASP- 107b is so large that its upper atmosphere must extend tens of thousands of miles out into space. This also makes it the first time that an extended atmos- phere has been discovered at in- frared wavelengths. Since its atmosphere is so ex- tended, the planet is losing a signif- icant amount of its atmospheric gases into space — between about 0.1 percent to 4 percent of its atmos- phere’s total mass every billion years. Stellar radiation has a significant effect on the rate at which a planet’s atmos- phere escapes. The star WASP-107 is highly active, supporting the atmospheric loss. As the atmosphere absorbs radiation it heats up, so the gas rapidly expands and escapes more quickly into space. As far back as the year 2000, it was predicted that helium would be one of the most readily-detectable gases on giant exoplanets, but until now, searches were unsuccessful. David Sing, co-author of the study also from the University of Exeter, concluded: “Our new method, along with future telescopes such as NASA’s James Webb Space Telescope, will allow us to analyze atmospheres of exoplanets in far greater detail than ever before.” ! JULY-AUGUST 2018 SPACE CHRONICLES E xoplanet WASP-107b is one of the lowest density planets known. While the planet is about the same size as Jupiter, it has only 12 percent of Jupiter’s mass. The exoplanet is about 200 light- years from Earth and takes less than six days to orbit its host star. Using in- frared spectroscopy, scientists using NASA’s Hubble Space Telescope were able to find helium in the escaping atmosphere of the planet — the first detection of this ele- ment in the atmosphere of an exoplanet. [ESA/Hubble, NASA, and M. Kornmesser]