Astronomers using the HARPS (High Accuracy Radial velocity Planet Searcher) spectrograph at ESO’s La Silla Observatory in Chile have detected gaseous magnesium (Mg), sodium (Na), calcium (Ca), chromium (Cr), iron (Fe), nickel (Ni) and vanadium (V) in the atmosphere of WASP-121b, a hot-Jupiter exoplanet approximately 881 light-years away in the constellation of Puppis.
The top of WASP-121b’s atmosphere is heated to a blazing 4,600 degrees Fahrenheit. Image credit: NASA / ESA / G. Bacon, STSci.
WASP-121b is a gas-giant planet 1.87 times bigger than Jupiter and 1.18 times more massive.
The planet is so close to WASP-121 that if it got any closer, the star’s gravity would start ripping it apart.
Astronomers estimate the planet’s temperature to be about 2,500 degrees Celsius (4,600 degrees Fahrenheit), hot enough to boil some metals.
“Earlier studies showed that there is a lot going on in its atmosphere,” said Dr. Jens Hoeijmakers, an astronomer in the National Centre of Competence in Research PlanetS at the Universities of Bern and Geneva.
“And this despite the fact that astronomers had assumed that ultrahot planets have rather simple atmospheres because not many complex chemical compounds can form in such blistering heat.”
“Previous studies tried to explain these complex observations with theories that did not seem plausible to me,” he said.
“Those studies had suspected that molecules containing the relatively rare metal vanadium were the main cause of WASP-121b’s complex atmosphere.”
“However, this would only make sense if a more common metal, titanium, were missing in the atmosphere. So we set out to find another explanation.”
Using data from the high-resolution HARPS spectrograph at ESO’s La Silla Observatory, Dr. Hoeijmakers and colleagues found magnesium, sodium, calcium, chromium, iron, nickel and vanadium in the atmosphere of WASP-121b.
“All metals evaporated as a result of the high temperatures prevailing on WASP-121b, thus ensuring that the air on the exoplanet consists of evaporated metals, among other things,” Dr. Hoeijmakers said.
“With the same techniques we use today, instead of just detecting signatures of gaseous iron or vanadium, we will be able to focus on biosignatures, signs of life such as the signatures of water, oxygen and methane.”
“The extensive knowledge about the atmosphere of WASP-121b not only confirms the ultrahot character of the exoplanet, but also underlines the fact that this field of research is entering a new era,” he said.
“After years of cataloguing what is out there, we are now no longer just taking measurements, but we are really beginning to understand what the data from the instruments show us.”
The team’s paper was published in the journal Astronomy & Astrophysics.
H.J. Hoeijmakers et al. 2020. Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS). IV. A spectral inventory of atoms and molecules in the high-resolution transmission spectrum of WASP-121b. A&A 641, A123; doi: 10.1051/0004-6361/202038365