Sun May Have Swallowed a Super-Earth, Study Suggests

The Sun has a couple of problems that astronomers can't quite explain. For decades, scientists have known that our star contains far less lithium than it should—roughly a hundredth of what the primordial cloud from which it formed billions of years ago ought to have left behind. And then there's the matter of sound. By listening to pressure waves that ripple through the Sun's interior, researchers can map its structure much the way seismologists map the Earth. But when they measure the speed of sound near the bottom of the convection zone—the churning layer just beneath the Sun's surface where heat moves through roiling plasma—the numbers don't match what their best models predict. Something is wrong, or at least something is missing from the picture.

Mutlu Yildiz, an astrophysicist at Ege University in Turkey, wondered whether a single explanation might account for both oddities. What if, he asked, the young Sun had swallowed a planet? Not a small one, but something substantial enough to leave a mark on the star's interior structure and chemistry even now, billions of years later. It's not an outlandish idea. Planetary migration is common in the universe—astronomers studying exoplanets around distant stars have found that planets routinely spiral inward or outward from their birth orbits. A rocky world forming close to the infant Sun, perhaps within Mercury's current orbit, could easily have been pulled into the star's gravitational embrace.

Yildiz built computer models of the Sun's evolution, testing different scenarios: planets of various sizes, different compositions, different orbital histories. He was looking for a configuration that could simultaneously reproduce the observed lithium depletion, the anomalous sound speeds, and other known features of the Sun like the depth of its convection zone. One model stood out. A super-Earth—a rocky planet roughly 5.6 times the mass of Earth—could do the job. Crucially, this hypothetical engulfed world would itself have been poor in lithium, which means its incorporation into the Sun wouldn't have added the missing element back. Instead, the planet's presence would have stirred the Sun's interior in ways that altered how heat and material moved through the star, changing the sound wave patterns we observe today.

The paper does not prove that such a planet exists, or ever existed, buried in the Sun's core. Yildiz is careful about that distinction. But the elegance of the model is striking: a single event—the consumption of one super-Earth during the Solar System's violent infancy—could resolve multiple long-standing puzzles about our star's current state. The model matches observations of the Sun's chemical composition, its internal structure, and the behavior of waves traveling through it. It's a coherent story, even if it remains unproven.

What comes next is observation. Yildiz and his colleagues believe that if such a planet was indeed swallowed, it may have left fingerprints in the Sun's interior that future helioseismic measurements could detect. The technology for mapping the Sun's insides has grown steadily more precise. Whether those fingerprints are actually there—whether the Sun really did consume a world—remains an open question. But for the first time, researchers have a testable hypothesis that could explain why our star seems, in several subtle ways, not quite like the models say it should be.