Scientists studying red dwarf stars—the smallest, coolest, and most common type in the universe—have discovered strong evidence that these stellar bodies can swallow entire planets during their early lives. A new study published in Monthly Notices of the Royal Astronomical Society reveals that six different red dwarfs across three separate star clusters show chemical signatures proving they have engulfed Earth-like rocky planets, overturning a long-held theory into observable fact.
The smoking gun was lithium, a chemical element that should not exist in red dwarfs. Researchers from Keele University and the University of Exeter, led by Professor Robin Jeffries, analyzed spectroscopic data from the Gaia-ESO Spectroscopic survey, examining thousands of stars across young clusters. The team found that six red dwarfs contained unusually high amounts of lithium—far more than their stellar siblings of similar types. "Red dwarfs are smaller and cooler than our sun but inside they are extremely hot," Jeffries explained. "This heat should destroy all of their fragile lithium in nuclear reactions shortly after they form." When lithium persists, it acts like a beacon of planetary consumption.
The reason is elegant. Young red dwarfs should burn away their lithium almost immediately through nuclear reactions at their cores. Yet these six stars retained detectable amounts. The only logical explanation: they had recently swallowed planetary material still rich in lithium from their surrounding systems. The analysis suggests each of these red dwarfs had engulfed between 3 to 10 Earth-masses of material—equivalent to consuming multiple Earth-like worlds in one gulp.
What makes this discovery particularly significant is how astronomers could confirm it. Studying isolated stars makes small chemical differences nearly impossible to detect. But stars born in clusters share a crucial advantage: they have well-understood ages and masses, born from the same cosmic material. This means even subtle chemical variations stand out clearly. "It's a bit like throwing paint onto a blank canvas," Jeffries said of the telltale lithium signature. Against the lithium-depleted backdrop of typical red dwarfs, the chemical fingerprints of these planet-eating stars become unmistakable.
Planetary engulfment during system formation has long been predicted by theory. Scientists have speculated that it may have happened even in our own solar system's early history, when gravitational interactions might have sent planets spiraling into the sun. But observational evidence has been scarce. This study changes that landscape, providing the first concrete detection of the phenomenon across multiple stars.
The discovery opens a new window into how planetary systems form and evolve during their most violent, chaotic youth. By studying the quantity and timing of planetary engulfment in different clusters, researchers can now trace the early biographies of stellar systems and understand which worlds survive to maturity and which are consumed. For a universe where billions of planetary systems have formed and evolved over billions of years, this finding suggests that planetary cannibalism is not a cosmic exception—it may be a normal part of how stars and their worlds are born.