An international team of astrophysicists at Aegean University in Turkey has proposed that the young Sun swallowed a super-Earth, a rocky planet five to ten times the mass of Earth, and that the chemical fingerprint of that event can still be detected deep inside the Sun today.
The researchers say the hypothesis could resolve three long-standing puzzles in solar physics at once, according to their study. For decades, standard models of the Sun built on stellar evolution physics have failed to reproduce several observed properties simultaneously.
The first problem is a mismatch between modeled and measured sound speed just below the Sun's convective zone, detected through helioseismology, the most precise tool available for probing a star's internal structure. The second is a discrepancy between the modeled and actual depth of that convective zone. The third is a severe shortage of lithium at the Sun's surface, roughly 140 times less than models predict it should contain. The team traced all three anomalies to a single event they say occurred 4.6 billion years ago, around the time the Solar System was forming.
How the model works
The researchers modeled two accretion episodes happening one after another. The first was the absorption of planetary material rich in heavy elements, the super-Earth itself. The second was the later infall of metal-poor gas from the leftover protoplanetary disk, the ring of material surrounding the young Sun after its planets had already formed.
The team said this sequence was not fitted by hand to produce the desired result. Instead, it reflects a genuine physical process: as planets form, they strip heavy elements out of the surrounding gas, so a star that later accretes disk material is pulling in gas that has already been depleted.
The DD1020 model
The team's central result is a model designated DD1020, with the absorbed planet nicknamed Dev Dilek, which satisfied all the observational constraints at once. The swallowed planet, with a mass of about 5.6 Earth masses (with broader versions of the model allowing five to ten Earth masses), left a local enrichment of heavy elements just below the convective zone, at a depth corresponding to 0.96 to 0.973 of the Sun's total mass.
That enrichment altered the composition and internal layering of the material there in a way that matches what would be needed to resolve the sound-speed and convective-zone-depth discrepancies, the researchers said.
The same model also accounted for the lithium shortfall. The team found that if the absorbed material was itself poor in lithium, and any additional turbulent mixing beneath the convective zone stayed shallow, the resulting lithium concentration at the surface matches what is actually observed. The mixing depth required for this to work is consistent with independent estimates for the tachocline, a transition region located in the upper third of the Sun.
Could a planet survive the plunge?
The authors did not stop at chemical modeling; they also tested whether the scenario was physically plausible. Their calculations show that a dense, rocky planet could pass through the convective envelope of the young Sun while losing almost none of its mass, since ordinary aerodynamic destruction and ablation would strip away only a negligible fraction of material.
That survival is helped by compression: as external pressure builds, the planet's radius shrinks to as little as 29 percent of its original size, reducing its effective cross-section and further limiting erosion. A separate stability analysis confirmed the planet would not be torn apart by tidal forces before reaching the stellar envelope.
Ruling out coincidence
A statistical test indicated the improved fit could not simply be explained by adding more tunable parameters to the model. Optimized control models that included turbulent mixing and a variable mixing parameter but no planet absorption produced only a partial match to observations and fell well short of the model that included the swallowed planet.
The next step, the researchers said, is to look for independent confirmation through further helioseismic or spectroscopic observations. If the chemical fingerprint of a super-Earth inside the Sun is confirmed, it would mean the star has been quietly preserving evidence of events from the era the Solar System formed, waiting to be uncovered.
