A scorching hot planet nearly 320 light-years from Earth has provided the first direct evidence for a fundamental assumption about how planets form. Astronomers discovered that WASP-189b shares an important chemical characteristic with its host star, supporting a long-standing idea that also helps scientists investigate potentially habitable worlds. The breakthrough came from the first simultaneous measurement of gaseous magnesium and silicon in an exoplanet's atmosphere, using the Gemini South telescope, part of the International Gemini Observatory, which is partially funded by the U.S.
National Science Foundation and operated by NSF NOIRLab. Located nearly 320 light-years away in the Libra constellation, WASP-189b belongs to an extreme category of planets called ultra-hot Jupiters (UHJ). These enormous worlds reach temperatures so intense that even materials normally found in solid rock can turn into gas.
Elements such as magnesium (Mg), silicon (Si), and iron (Fe) can therefore be detected in their atmospheres. Astronomers identify these substances through spectroscopy, a method that separates light into different wavelengths to reveal the chemicals present. An international research team led by Jorge Antonio Sanchez, a graduate student at Arizona State University (ASU), investigated WASP-189b with the high-resolution Immersion GRating INfrared Spectrograph (IGRINS).
At the time, the instrument was installed on the Gemini South telescope in Chile.[1] For the first time, researchers were able to measure magnesium and silicon together in the atmosphere of a planet beyond our Solar System. Their observations revealed that the proportion of magnesium to silicon on WASP-189b closely matches the ratio found in its parent star. This result provides the first direct observational support for a widely used assumption about the chemical relationship between stars and their planets, offering a valuable new way to investigate planetary origins and evolution.
"These discoveries show Gemini's ability to help us understand the characteristics of the remarkable zoo of exoplanets in our solar neighborhood," says Chris Davis, NSF Program Director for NOIRLab. "Such discoveries are only possible because of Gemini's cutting-edge instruments." A Long-Suspected Connection Between Stars and Planets Astronomers believe that giant planets such as WASP-189b formed within enormous disks of gas and dust surrounding young stars. These structures, called protoplanetary disks, provide the raw materials from which planets develop.
The chemical makeup of a giant planet's outer atmosphere is thought to retain clues about the environment where it originally formed. Because stars and their surrounding disks originate from the same cloud of material, scientists have long assumed that they contain similar proportions of rock-forming elements. In particular, the ratios of these elements in a disk are expected to resemble those measured in its central star.
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