The latest observations by astronomers show that the elemental composition of a giant exoplanet named WASP-189b in its atmosphere is highly consistent with that of its parent star, providing the first direct evidence for a core hypothesis of how planets form and evolve. This achievement is considered an important milestone in the field of astrobiology.
For the first time, the research team simultaneously detected gaseous magnesium and silicon in the atmosphere of an exoplanet, and used this to compare the chemical abundance ratio of the planet and its parent star. The observations were made by the Gemini South Telescope in Chile, part of the International Gemini Observatory, funded in part by the U.S. National Science Foundation (NSF) and operated through NOIRLab.
The target planet WASP-189b is nearly 320 light-years away from the Earth and located in the constellation Libra. It is a type of exoplanet known as an "ultra-hot Jupiter". Such planets orbit very close to their stars, and their surface temperatures are high enough to vaporize rock-forming elements such as magnesium (Mg), silicon (Si), and iron (Fe). Therefore, they provide ideal conditions for analyzing the chemical composition of the atmosphere using high-resolution spectroscopy techniques.
The research was led by Arizona State University graduate student Jorge Antonio Sanchez. The team used the high-resolution infrared imaging grating spectrometer IGRINS installed on the Gemini South telescope to conduct precise measurements of the atmosphere of WASP-189b. Instrumental data show that the ratio of magnesium to silicon in the planet's atmosphere is highly consistent with that of its parent star.
This result provides the first direct observational support for a key inference that has long existed in planet formation theories: planets are born in protoplanetary disks around young stars. The gas and dust in the protoplanetary disk originate from the same collapsed interstellar cloud as the star, so the two should "mirror" each other in terms of overall chemical composition. Prior to this, this "star-planet composition correspondence" mainly came from indirect deductions between the inner planets and the sun, and has not yet been directly confirmed in the exoplanet system.
Sanchez pointed out that WASP-189b provides an important observational "anchor" for understanding the formation of Earth-like planets. By precisely determining the ratios of key rock-forming elements between a star and its planets, researchers can more confidently use information about a star's chemistry to infer the overall composition of the solid material that formed around the star, including potential Earth-like planets.
From an astrobiological perspective, this chemical correspondence between stars and planets is of great significance. The abundance of elements in a star affects the abundance and distribution of rocky material and volatiles in the protoplanetary disk, which further affects the planet's ability to maintain a magnetic field, drive plate tectonics, and continuously release the chemicals needed for life into the atmosphere, oceans, and soil through volcanoes and geological cycles. By analyzing a star's chemical fingerprint, scientists can hopefully provide a first estimate of the potential habitability of rocky planets in its planetary system.
Michael Line, co-author of the paper and associate professor at Arizona State University, said the study demonstrates the power of ground-based high-resolution spectrometers in constraining key rock-forming elements such as magnesium and silicon, which are the building blocks for building rocky Earth-like planets. He believes that this technological progress opens up a whole new dimension for studying exoplanet atmospheres.
Looking forward to the future, the scientific research team expects that by conducting high-resolution observations in a wider range of wavelengths, it can further draw a "component panorama" of exoplanet atmospheres, including WASP-189b. This will help scientists more systematically understand the entire process of planets' birth, migration and evolution from the protoplanetary disk, and evaluate whether different planets have the potential to support life in terms of physical and chemical conditions.
Relevant research was published in an academic journal in February 2026 under the title "A Stellar magnesium to silicon ratio in the atmosphere of an exoplanet", which further discussed the importance of stellar magnesium to silicon ratio in planet formation and internal structure inference from a theoretical and observational level.