The Dark Energy Spectroscopic Instrument (DESI), built primarily to map the large‑scale structure of the universe by measuring galaxy spectra, has also collected serendipitous data during intervals when its main targets were not observable. In those periods the instrument turned its gaze toward distant white dwarfs and recorded their spectra.
Within those spectra astronomers detected clear signatures of elements typical of rocky material – iron, magnesium, silicon and oxygen. The presence of these heavy elements in the otherwise pristine atmospheres of white dwarfs indicates that the stars are accreting debris from disintegrating exoplanets. This accretion happens when a planet ventures close enough to the compact star that tidal forces rip it apart, and the resulting dust and gas fall onto the stellar surface.
The measured abundances match remarkably well the composition of rocky bodies in the inner Solar System, such as Earth and the asteroid belt. This suggests that the building blocks of terrestrial planets in other planetary systems are similar to those in our own neighbourhood, bolstering the idea that Earth‑like worlds may be more common than previously thought.
The approach demonstrates that spectroscopy of white dwarfs can serve as a powerful probe of exoplanet geology. Future observations with DESI and comparable facilities could uncover many more such systems, enabling a statistical analysis of rocky exoplanet composition across the Galaxy.