Gemini South Telescope Reveals Exoplanet's Composition Matches Host Star

Astronomers discover first direct evidence of a foundational concept in astrobiology

Apr. 2, 2026 at 5:34am

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Astronomers have discovered that the giant exoplanet WASP-189b has a composition that directly matches its host star, providing the first observational evidence of a widely adopted assumption about planet formation. This breakthrough was achieved using the Gemini South telescope's high-resolution spectrograph to simultaneously measure the magnesium and silicon content in the planet's atmosphere.

Why it matters

This finding validates the assumption that the ratio of rock-forming elements in a protoplanetary disk matches that of the host star, which is a foundational concept in astrobiology and the study of habitable exoplanets. By measuring a star's chemical composition, scientists can now more accurately infer the abundances of key elements in its orbiting planets, which is crucial for understanding planetary formation, evolution, and potential habitability.

The details

The team of astronomers, led by graduate student Jorge Antonio Sanchez from Arizona State University, observed the ultra-hot Jupiter exoplanet WASP-189b using the high-resolution Immersion GRating INfrared Spectrograph (IGRINS) mounted on the Gemini South telescope in Chile. This powerful instrument allowed them to simultaneously measure the magnesium and silicon content in the planet's atmosphere, a first-of-its-kind observation. The data revealed that WASP-189b shares the same magnesium-to-silicon ratio as its host star, providing the first direct evidence of the assumed chemical link between a star and the planets that form around it.

  • The observations of WASP-189b were conducted in 2022 and 2023 when IGRINS was a visiting instrument at the Gemini South telescope in Chile.
  • IGRINS-2, a new iteration of the instrument, has since been commissioned as a facility instrument for the Gemini North telescope in Hawaii.

The players

Jorge Antonio Sanchez

A graduate student at Arizona State University who led the research team.

Gemini South Telescope

One half of the International Gemini Observatory, a facility funded by the U.S. National Science Foundation and operated by NSF NOIRLab.

IGRINS

The high-resolution Immersion GRating INfrared Spectrograph instrument that was used to make the observations of WASP-189b.

Chris Davis

NSF Program Director for NOIRLab.

Michael Line

Associate Professor at Arizona State University and a co-author of the study.

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What they’re saying

“These discoveries show Gemini's ability to help us understand the characteristics of the remarkable zoo of exoplanets in our solar neighborhood. Such discoveries are only possible because of Gemini's cutting-edge instruments.”

— Chris Davis, NSF Program Director for NOIRLab

“WASP-189b gives us a much-needed observational anchor in our understanding of terrestrial planet formation since it offers a measurable quantity that validates the presumed resemblance of stellar composition and the proportion of rocky material around host stars used to form planets.”

— Jorge Antonio Sanchez, Graduate student, Arizona State University

“Our study demonstrates the capability of ground-based, high-resolution spectrographs to constrain critical species like magnesium and silicon, which are two elemental building blocks from which rocky planets form. This advancing capability opens an entirely new dimension in our study of exoplanet atmospheres.”

— Michael Line, Associate Professor, Arizona State University

What’s next

Further multi-wavelength, high-resolution observations of exoplanet atmospheres like that of WASP-189b will help reveal the larger chemical inventory that exists within distant worlds, enabling deeper insights into the conditions that govern planetary origins, evolution, and potential habitability.

The takeaway

This discovery provides the first direct observational evidence validating the foundational assumption that the chemical composition of a star is reflected in the planets that form around it. This represents a significant step forward in our understanding of exoplanet formation and the search for habitable worlds beyond our solar system.