Record-breaking: Astronomers detect heaviest element ever found on exoplanet 556 light years from Earth

How was Samarium found on the ultra-hot gas giant?

The element was discovered on MASCARA-4b, an "ultra-hot Jupiter" exoplanet located nearly 556 light years away from Earth. The exoplanet has a temperature of 2,250 K and orbits a bright A-type young star. These types of stars are noted to be only a few hundred million years old and emit infrared radiation. 

“Ultra-hot Jupiters (UHJs) possess the most extreme environments among various types of exoplanets, making them ideal laboratories to study the chemical composition and kinetics properties of exoplanet atmosphere with high-resolution spectroscopy (HRS),” the authors stated in their research paper. 

This gas giant completes one orbit every 2.82 days, and the estimated distance between them is 0.047 AU.

The team observed two MASCARA-4 b transits on February 13, 2020, and March 1, 2020. This helped them measure the starlight and detect the elements in the atmosphere. They used the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) to do so. This high-resolution spectrograph is installed on the European Southern Observatory's (ESO) Very Large Telescope (VLT) in Cerro Paranal, Chile.

The observations led to the detection of several heavier elements in the atmosphere of MASCARA-4 b, including rubidium (Rb) and ions of titanium (Ti+) and barium (Ba+). 

According to the study, this is the first time Rb and Sm have been discovered in the atmosphere of a distant exoplanet, whereas Ti+ and Ba+ have previously been found in extrasolar planets.

The study is led by a team of astronomers from Beijing's Chinese Academy of Sciences (CAS), and the paper has been accepted for publication in The Astronomical Journal. The results are available on the arXiv pre-print server. 

Following that, the researchers plan to conduct additional observations to quantify and confirm the presence of these new elements in the exoplanet's atmosphere. 

Study Abstract:

Ultra-hot Jupiters (UHJs) possess the most extreme environments among various types of exoplanets, making them ideal laboratories to study the chemical composition and kinetics properties of exoplanet atmosphere with high-resolution spectroscopy (HRS). It has the advantage of resolving the tiny Doppler shift and weak signal from exoplanet atmosphere and has helped to detect dozens of heavy elements in UHJs including KELT-9b, WASP-76b, WASP-121b. MASCARA-4b is a 2.8-day UHJ with an equilibrium temperature of ∼2250 K, which is expected to contain heavy elements detectable with VLT. In this letter, we present a survey of atoms/ions in the atmosphere of the MASCARA-4b, using the two VLT/ESPRESSO transits data. Cross-correlation analyses are performed on the obtained transmission spectra at each exposure with the template spectra generated by petitRADTRANS for atoms/ions from element Li to U. We confirm the previous detection of Mg, Ca, Cr and Fe and report the detection of Rb, Sm, Ti+ and Ba+ with peak signal-to-noise ratios (SNRs) > 5. We report a tentative detection of Sc+, with peak SNRs ∼6 but deviating from the estimated position. The most interesting discovery is the first-time detection of elements Rb and Sm in an exoplanet. Rb is an alkaline element like Na and K, while Sm is the first lanthanide series element and is by far the heaviest one detected in exoplanets. Detailed modeling and acquiring more data are required to yield abundance ratios of the heavy elements and to understand better the common presence of them in UHJ's atmospheres.