Utilizing the Immersion Grating Infrared Spectrometer (IGRINS) aboard the Gemini South telescope, which is part of the International Gemini Observatory, scientists have achieved a direct measurement of the atmospheric constituents of WASP-189b. The findings reveal a composition that mirrors the elemental makeup of its parent star, providing the most compelling evidence to date that celestial bodies acquire their chemical signatures from the nascent disks from which they originate.
An artist’s impression of an ultrahot Jupiter. Image credit: Sci.News.
WASP-189, an A-type star situated 322 light-years distant within the constellation Libra, has an estimated age of 730 million years.
This star, also identified as HD 133112, surpasses the Sun in size and is over 2,000 degrees Celsius hotter.
First observed in 2018, WASP-189b is classified as a transiting gas giant, possessing a radius approximately 1.6 times that of Jupiter.
The exoplanet orbits its star at a proximity roughly 20 times closer than Earth’s distance from the Sun, completing a full revolution in a mere 2.7 days.
“The extreme temperatures experienced by ultra-hot Jupiters are sufficient to vaporize elements crucial for rock formation, such as magnesium, silicon, and iron. This presents a unique opportunity to detect these elements through spectroscopy, a method involving the dispersion of light into its constituent wavelengths to ascertain the presence of specific chemical substances,” explained Jorge Antonio Sanchez, a graduate student at Arizona State University, alongside his research collaborators.
The astronomers procured high-resolution thermal emission spectra of WASP-189b utilizing the IGRINS instrument.
Within the exoplanet’s atmosphere, they identified neutral iron, magnesium, silicon, water, carbon monoxide, and hydroxyl.
“The data acquired by IGRINS indicate that WASP-189b exhibits the identical magnesium-to-silicon ratio as its host star,” the researchers noted.
“This discovery offers the inaugural empirical validation of a widely accepted tenet of planet formation theory, thereby inaugurating a new avenue for comprehending the processes of exoplanet formation and evolution.”
It is postulated that hot giant planets like WASP-189b possess an outer gaseous envelope whose chemical composition is shaped by the protoplanetary disk—the disk of material from which they coalesced.
Researchers generally assume that the proportions of rock-forming elements within a protoplanetary disk closely match those of the parent star, given their shared origin from the same primordial cosmic material.
This presupposed chemical connection between a star and its orbiting planets is a standard practice in modeling the composition of rocky exoplanets.
Prior to these recent findings, this inference was predominantly based on observations within our own Solar System, and direct empirical verification on exoplanets had not been achieved until now.
“WASP-189b provides a crucial observational benchmark for our understanding of terrestrial planet formation. It offers a quantifiable metric that corroborates the assumed stoichiometric similarity between stellar material and the proportion of rocky constituents in the environment around host stars where planets form,” stated Sanchez.
“Our investigation demonstrates the efficacy of ground-based, high-resolution spectrographic instruments in constraining the abundance of vital elements like magnesium and silicon, which are fundamental building blocks for rocky planet development,” added Dr. Michael Line, an astronomer affiliated with Arizona State University.
“This evolving capability unlocks an entirely novel dimension in our exploration of exoplanetary atmospheres.”
A research article detailing these discoveries was published on February 18, 2026, in the esteemed journal Nature Communications.
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J.A. Sanchez et al. 2026. A Stellar magnesium to silicon ratio in the atmosphere of an exoplanet. Nat Commun 17, 2902; doi: 10.1038/s41467-026-69610-x
