Terbium, a chemical element with the symbol Tb and atomic number 65, has never before been seen in an exoplanet atmosphere.
This illustration shows how the ultrahot Jupiter KELT-9b sees its host star. Image credit: NASA’s Goddard Space Flight Center / Chris Smith, USRA.
First discovered in 2016, KELT-9b is a gas giant approximately 2.8 times more massive than Jupiter but only half as dense.
This exoplanet orbits KELT-9 — the hottest, most massive and brightest star yet found to host a transiting giant planet — once every 36 hours.
At approximately 9,900 degrees Celsius (17,850 degrees Fahrenheit), the host star is at the dividing line between stars of type A and B.
Also known as HD 195689, the star is about 650 light-years away in the constellation of Cygnus.
KELT-9b is tidally locked to the star and its day side is perpetually bombarded by stellar radiation.
With a day-side temperature peaking at 4,327 degrees Celsius (7,820 degrees Fahrenheit), the planet is hotter than most stars.
“We have developed a new method that makes it possible to obtain more detailed information,” said Lund University Ph.D. student Nicholas Borsato.
“Using this, we have discovered seven elements, including the rare substance terbium, which has never before been found in any exoplanet’s atmosphere.”
Terbium is a silvery-white, rare earth metal that is malleable, and ductile.
Discovered in 1843 by the Swedish chemist Carl Gustaf Mosander, it belongs to the so-called lanthanides (lanthanoids).
The metal is very rare in nature, and 99% of the world’s terbium production today takes place in the Bayan Obo mining district in Inner Mongolia.
“Finding terbium in an exoplanet’s atmosphere is very surprising,” Borsato said.
Thanks to their method, Borsato and colleagues filtered out the dominant signals in KELT-9 b’s atmosphere.
This opens up the possibility of finding out more about the atmospheres of other exoplanets.
“Detecting heavy elements in the atmospheres of ultra-hot exoplanets is another step towards learning how the atmospheres of planets work,” Borsato said.
“The better we get to know these planets, the greater chance we have of finding Earth 2.0 in the future.”
The team’s paper will be published in the journal Astronomy & Astrophysics.
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N.W. Borsato et al. 2023. The Mantis Network III: Expanding the limits of chemical searches within ultra hot-Jupiters. New detections of Ca I, V I, Ti I, Cr I, Ni I, Sr II, Ba II, and Tb II in KELT-9 b. A&A, in press; arXiv: 2304.04285
