When some stars die, they leave behind a hot, dense core called a white dwarf. Scientists using the DESI telescope in the Arizona desert have caught these white dwarfs in the act of swallowing broken pieces of planets—and what they found is striking: the debris matches the same rocky materials that make up Earth and its neighbors.
Paula Izquierdo of the University of Warwick led the research. She says the team was able to study these rare objects because DESI—built to map distant galaxies—sometimes had to wait for better conditions. Rather than sitting idle, the telescope turned to look at closer targets. "We are lucky enough to get a lot of white dwarfs observed as a side project," Izquierdo said. "Among those, we found these ones which are super metal-enriched."
The study looked closely at 12 white dwarfs carrying unusually high amounts of heavy elements like oxygen, magnesium, silicon, calcium, and iron—the same materials that form rocks on Earth. Six of them had clear enough data for detailed analysis. Four showed compositions similar to dry, rocky planets. Two others showed signs of water-bearing materials, possibly similar to the young Earth before it dried out. "Most of the accreted bodies by white dwarfs show the major rock-forming elements that we see in our solar system, resembling the composition seen in primitive meteorites," Izquierdo explained.
The findings, published in the Monthly Notices of the Royal Astronomical Society, suggest our solar system's chemistry may not be unusual at all. Between 20 and 50 percent of white dwarfs carry traces of swallowed planets in their atmospheres. Scientists have identified about 1,750 that are actively feeding on planetary debris. Only a few dozen of these have clear enough spectra to study in detail, making DESI's contribution especially valuable.
The research offers a window into the chemistry of worlds we will never visit directly. By studying these destroyed planets, astronomers can compare rocky exoplanets across the galaxy to our own. DESI continues its work, and each new observation adds another piece to the puzzle of whether Earth-like worlds are common or rare.
The instrument was designed for a completely different purpose, but the team has shown it to be an excellent tracer of these metal-rich stars. Further analysis could reveal new clues about the thousands of rocky exoplanets already discovered—and what conditions are needed for a planet like ours to form.