Alien Planet Eater: The Superheated Exoplanet That Possibly Ingested Its Lesser Companion

An incredibly hot behemoth exoplanet, WASP-76 b, studied in this report, orbits perilously close to its parent star. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani

A multinational team of researchers, armed with the MAROON-X device, has successfully identified and quantified 11 different chemical elements in the superheated atmosphere of WASP-76 b. Unexpectedly high levels of these elements hint that this exoplanet might have engulfed a smaller, Mercury-esque planet. The team’s research further illustrates the significant impact temperature has on the chemical composition of giant planet atmospheres.

Research Scientist Mohamad Ali-Dib from the Center for Astro, Particle, and Planetary Physics at NYU Abu Dhabi, along with a global team led by Université de Montréal, recently unveiled an in-depth analysis of the superhot giant exoplanet WASP-76 b in the prestigious Nature journal.

Utilizing the MAROON-X instrument attached to the Gemini-North Telescope, the team succeeded in identifying and gauging the abundance of 11 chemical elements in the planet’s atmosphere, including elements associated with rock formation, the abundances of which are unknown even for our Solar System’s giant planets, such as Jupiter or Saturn. The concentrations of these chemicals provide clues about the planets’ formation and evolution. They reveal the original building materials of the planet and any substantial pollutants that were later accreted or ingested. The team proposed, based on irregularities in these chemical levels, that WASP-76 b may have swallowed a Mercury-like planet.

Ali-Dib, who spearheaded the data modelling, remarked, “This is the inaugural study to ascertain the abundances of elements like nickel, magnesium, and chromium with high precision in any giant planet. The variations we noted in their values led us to speculate that WASP-76 b might have consumed a significantly smaller planet with a similar chemical make-up to Mercury.”

WASP-76 b orbits an enormous star 634 light-years away in the Pisces constellation. Being approximately 12 times closer to its star than Mercury is to the Sun, the planet endures blistering temperatures well over 2000°C.

At these high temperatures, elements that would typically form rocks on Earth, such as magnesium and iron, are vaporized and exist in gaseous state in the upper atmosphere. The study of this unique planet offers unmatched insight into the presence and quantity of rock-forming elements in giant planets. In cooler giants like Jupiter, these elements are found lower in the atmosphere and are thus undetectable.

The discovery team also observed that the observed composition of giant planets’ upper atmospheres can be highly temperature-sensitive, even in extremely hot planets. Depending on an element’s condensation temperature, it will either be in gaseous form in the upper atmospheric layers or condense into liquid form and descend to deeper regions. As a gas, it significantly contributes to light absorption and can be observed by astronomers. However, when it condenses, it becomes invisible to observers and completely absent from their observations. This could clarify why certain elements like titanium and aluminium were not detected.

For more information on this study:

Examining a Blistering-Hot Exoplanet
Revealing the Vaporized Rock Atmosphere of a Hot Jupiter

Reference: “Vanadium oxide and a sharp onset of cold-trapping on a giant exoplanet” by Stefan Pelletier, Björn Benneke, Mohamad Ali-Dib, Bibiana Prinoth, David Kasper, Andreas Seifahrt, Jacob L. Bean, Florian Debras, Baptiste Klein, Luc Bazinet, H. Jens Hoeijmakers, Aurora Y. Kesseli, Olivia Lim, Andres Carmona, Lorenzo Pino, Núria Casasayas-Barris, Thea Hood and Julian Stürmer, 14 June 2023, Nature.
DOI: 10.1038/s41586-023-06134-0

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• Vanadium oxide and a sharp onset of cold-trapping on a giant exoplanet
• Exoplanet WASP-76 b
• MAROON-X Instrument
• Center for Astro, Particle, and Planetary Physics at NYU Abu Dhabi