Free Astronomy Magazine July-August 2026

23 ASTRO PUBLISHING the magnesium and silicon content of the exoplanet’s atmosphere. This is the first time such a measurement has been made, and the data reveal that WASP-189 b shares the same magnesium-to-silicon ratio as its host star. This finding provides the first observational evidence of a widely adopted assumption about planet formation, and opens a new route to understand how exoplan- ets form and evolve. “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.” Hot giant planets like WASP-189 b are thought to have an outer layer of gas that has a chemical composi- tion influenced by the disk of mate- rial in which they formed, known as protoplanetary disks. And re- searchers assume that the ratio of rock-forming elements in a proto- planetary disk matches that of the host star, since the two were born from the same primordial cloud of material. This inferred chemical link between a star and the planets that form around it is commonly used to model the composition of rocky ex- oplanets. This link was previously based on measurements within our Solar System, and it had not been directly observed on planets else- where, until now. “WASP-189 b gives us a much- needed observational anchor in our understanding of terrestrial planet formation since it offers a meas- urable quantity that validates the presumed resemblance of stellar composition and the proportion of rocky material around host stars used to form planets,” says Sanchez. This assumption is not only useful for understanding planet forma- tion, but it is also foundational to the field of astrobiology, which in- cludes the study of habitable envi- ronments in the Solar System. By measuring the chemical composi- tion of a star, scientists can infer the abundances of rock-forming ele- ments in the star’s exoplanets, which can dictate the geochemical conditions that make a planet hab- itable. For instance, the rock-form- ing elements in Earth are in-part responsible for our protective mag- netic field, plate tectonics, and driv- ing the release of life-sustaining chemicals into our atmosphere, oceans, and soil. As the exoplanet field looks to- wards the characterization of ter- restrial planets, and seeks to eluci- date the habitable conditions of rocky worlds, empirical evidence validating the relationship between stellar and planetary compositions represents a fundamental step for- ward. And the level of spectral res- olution necessary for these types of studies is currently only available on ground-based telescopes. “Our study demonstrates the capa- bility of ground-based, high-resolu- tion spectrographs to constrain critical species like magnesium and silicon, which are two elemental building blocks from which rocky planets form,” says study co-author Michael Line, Associate Professor at ASU. “This advancing capability opens an entirely new dimension in our study of exoplanet atmos- pheres.” Further multi-wavelength, high-res- olution observations to study exo- planet atmospheres like that of WASP-189 b will help reveal the larger chemical inventory that exists within distant worlds. Such studies will enable deeper insights into the conditions that govern planetary origins, evolution, and potential habitability. JULY-AUGUST 2026 !