A team of astronomers from the University of Groningen, the University of Edinburgh, and SRON Netherlands Institute for Space Research has detected chromium hydride (CrH) in the transmission spectra of the hot-Jupiter exoplanet WASP-31b.
An artist’s impression of a hot-Jupiter exoplanet. Image credit: ESA / ATG Medialab / CC BY-SA 3.0 IGO.
WASP-31b orbits the 1-billion-year-old F-type star WASP-31, which is located about 1,305 light-years away in the constellation of Crater.
Discovered by 2011, the planet has a mass of 0.5 times that of Jupiter and a radius of 1.5 Jupiter radii, making it one of the lowest density exoplanets known to date.
Orbiting at a distance of 0.047 AU from its host star, it has a temperature of 1,120 degrees Celsius (2,048 degrees Fahrenheit).
In a new study, Dr. Marrick Braam and his colleagues re-analyzed the publicly available transmission spectra of WASP-31b obtained by the NASA/ESA Hubble Space Telescope.
“From so-called transmission spectra we deduce which substances are in the atmosphere of an exoplanet,” they said.
“Those could one day give an indication of extraterrestrial life.”
“Or they can show that there is a condition for life, such as a weather system. For the time being, however, this type of research is limited to giant planets close to their stars, so-called hot Jupiters.”
“These planets are too hot to expect life, but they can already teach us a lot about how possible weather systems work.”
The astronomers found evidence for the spectroscopic signatures of chromium hydride as well as water and potassium in the atmosphere of WASP-31b.
“WASP-31b is a hot Jupiter with a temperature of about 1,120 degrees Celsius in the twilight zone between day and night — the place where starlight travels through the atmosphere towards Earth,” they said.
“And that happens to be around the temperature at which chromium hydride transitions from liquid to gas at the corresponding pressure in the outer layers of the planet, similar to the conditions for water on Earth.”
“Chromium hydride could play a role in a possible weather system on this planet, with clouds and rain,” Dr. Braam said.
“It is the first time that chromium hydride is found on a hot Jupiter and therefore at the right pressure and temperature.”
The results appear in the journal Astronomy & Astrophysics.
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Marrick Braam et al. 2021. Evidence for chromium hydride in the atmosphere of hot Jupiter WASP-31b. A&A 646, A17; doi: 10.1051/0004-6361/202039509
