Study suggests sun may carry 'fingerprints' of engulfed super-Earth

The sun may have swallowed a planet billions of years ago, and the evidence might still be written into its interior. That is the argument of a new study published in Monthly Notices of the Royal Astronomical Society, which proposes that the young sun engulfed a super-Earth—a planet several times more massive than our own—and that this ancient collision left behind chemical and structural signatures that astronomers could potentially detect today.

Mutlu Yildiz, a professor at Ege University in Turkey, led the research. His team modeled the sun's evolution over time and compared those models against precise measurements of the sun's interior structure. What they found was intriguing: if the young sun had indeed consumed a super-Earth, it would help resolve two long-standing puzzles that have vexed solar physicists for years. The first involves the sound-speed structure just below the sun's convection zone and the depth of that zone itself—features that standard stellar models have struggled to reproduce accurately. The second is the sun's unusually depleted lithium abundance at its surface, a depletion that has never been fully explained.

Yieldiz and his colleagues wondered whether these two separate mysteries might share a common cause rooted in the sun's early chemical history. Young stars, they reasoned, are surrounded by disks of material where planets form and where material can flow between the disk and the star itself. If a planet made of different chemical material than the surrounding gas had fallen into the young sun, it could have left a lasting imprint—a fingerprint, as the researchers call it—deep within the star's interior.

To test this idea, the team used MESA, a sophisticated code for modeling stellar evolution. They ran simulations exploring different scenarios of planetary accretion and compared the results against helioseismic observations—measurements of vibrations in the sun that reveal its internal structure—as well as measurements of surface chemical abundances. They also tested alternative explanations involving the sun's equation of state, opacity, and the physics of convective mixing. What emerged from this analysis was a surprisingly narrow answer: the young sun most likely engulfed a super-Earth somewhere between five and ten times Earth's mass.

What struck Yieldiz most was that this single scenario did more than solve one problem. It simultaneously matched multiple independent observations of the sun—its interior structure, its lithium depletion, and other measurements. "We thought planetary engulfment might affect the solar structure but did not expect the calculations to converge on such a specific super-Earth mass range," he said. The modeling also revealed something unexpected about the physics of planetary destruction: a super-Earth could pass through the sun's outer layers while losing very little mass, meaning planets might leave detectable fingerprints inside their host stars long after they have been consumed.

This work builds on a theoretical foundation laid about a decade ago, when researchers proposed that one or more super-Earths could have formed inside Mercury's orbit and migrated inward through the protoplanetary disk, potentially falling into the young sun. That earlier study provided a plausible pathway for such an event but did not require that it actually happened. Yieldiz's new work takes the next step: it asks whether the sun itself could still carry observable evidence that such an engulfment actually occurred, and the answer appears to be yes.

The finding also touches on a broader astronomical puzzle. Many other star systems appear to harbor large super-Earths, yet our own solar system has none. One explanation for this absence is that our sun may have consumed its super-Earths early on, before the planetary system we know today took shape. If that is true, the chemical and structural signatures of those lost worlds might still be readable in the sun's interior.

Yieldiz acknowledged that definitively proving the sun swallowed a planet may not be possible. But he expressed confidence that if the predicted signatures could be independently identified through helioseismic observations or other means, it would provide strong evidence for an engulfment event that occurred billions of years ago. The next phase of research, he said, is to see whether these fingerprints can actually be detected.