Last week, astronomers detected the heaviest element, Samarium, on an exoplanet. The element was discovered on an ultra-hot Jupiter exoplanet located 556 light years from Earth.
On the heels of the previous discovery, scientists have detected another element, Terbium, in an exoplanet’s atmosphere for the first time. Known as KELT-9, the exoplanet is said to be the galaxy’s hottest, orbiting its distant star about 670 light years from Earth.
KELT-9, which has an average temperature of 4,000 degrees Celsius, has always been a subject of fascination with astronomers, ever since its discovery in 2016.
The finding was made possible thanks to a new method developed by researchers at Lund University in Sweden.
“We have developed a new method that makes it possible to obtain more detailed information. Using this, we have discovered seven elements, including the rare substance terbium, which has never before been found in any exoplanet’s atmosphere,” Nicholas Borsato, a Ph.D. student in astrophysics at Lund University, said in a statement.
What is Terbium?
The rare earth metal belongs to the lanthanoid group of chemical elements. Discovered in 1843 by the Swedish chemist Carl Gustaf Mosander in the Ytterby mine in the Stockholm archipelago, the metal is considered very rare – 99 percent of the world’s terbium production takes place in the Bayan Obo mining district in Inner Mongolia.
And so, naturally, the astronomers were taken aback when they detected the element in an exoplanet’s atmosphere.
Usually, exoplanets are discovered based on the measurements of how brightly stars shine. According to the release, when an exoplanet passes before its star, the star’s brightness decreases. Now, thanks to the researchers’ advanced methods, dominant signals in KELT-9 b’s atmosphere can be filtered out, thereby opening up the possibility of finding out more about the atmospheres of other planets.
“Learning more about the heavier elements helps us, among other things, to determine the age of the exoplanets and how they were formed,” said Borsato.
“Detecting heavy elements in the atmospheres of ultra-hot exoplanets is another step towards learning how the atmospheres of planets work. The better we get to know these planets, the greater chance we have of finding Earth 2.0 in the future,” he added.
The new study has been published in Astronomy & Astrophysics.
Study Abstract:
Cross-correlation spectroscopy is an invaluable tool in the study of exoplanets. However, aliasing between spectral lines makes it vulnerable to systematic biases. This work strives to constrain the aliases of the cross-correlation function to provide increased confidence in the detections of elements in the atmospheres of ultra-hot Jupiters (UHJs) observed with high-resolution spectrographs. We use a combination of archival transit observations of the UHJ KELT-9 b obtained with the HARPS-N and CARMENES spectrographs and show that it is possible to leverage each instrument’s strengths to produce robust detections at substantially reduced signal-to-noise. Aliases that become present at low signal-to-noise regimes are constrained through a linear regression model. We confirm previous detections of H I, Na I, Mg I, Ca II, Sc II, Ti II, Cr II, Fe I, and Fe II, and detect eight new species Ca I, Cr I, Ni I, Sr II, Tb II at the 5σ level and Ti I, V I, Ba II above the 3σ level. Ionised terbium (Tb II) has never before been seen in an exoplanet atmosphere. We further conclude that a 5σ threshold may not provide a reliable measure of confidence when used to claim detections, unless the systematics in the cross-correlation function caused by aliases are taken into account.
