Astronomers have long been puzzled as to why a type of planet that is common in the cosmos is missing from our solar system: a super-Earth. Such rocky planets weigh between two and ten Earth masses and thus close the gap between smaller, Earth-like planets and large gas and ice giants. At the same time, our sun also shows some unusual features that are difficult to reconcile with astrophysical models: the lithium content on its surface is too low and the convection zone, characterized by plasma circulation, extends deeper than it should.

Planetary catastrophe as an explanation?

But what is the reason for this? Astronomers led by Mutlu Yildiz from Ege University in Izmir have now examined a possible explanation in more detail. Since 2016, some astronomers have suspected that there could have been another planet within Mercury’s orbit in the early days of the solar system. However, the Sun’s powerful tidal forces knocked this young super-Earth out of its orbit and sent it crashing into the Sun, similar to what has been observed with some exoplanets on a “death course.”

However, until now there has been a lack of evidence of such a planetary catastrophe in the young solar system. “We therefore wanted to know whether the sun itself could still contain traces of this devouring,” explains Yildiz. “Because the material of planets is different from that of the stellar gas disk, such an event could have left a chemical signature inside the Sun.” Using an astrophysical model, the astronomers reconstructed different versions of an entangled super-Earth and the possible consequences. They then checked whether this could explain the sun’s peculiarities.

Fall below the convection zone

The result: Both the lack of lithium on the sun’s surface and the unusual thickness of the solar convection zone could be explained by the early fall of a super-Earth into the sun. “Our study suggests that a planet weighing several Earth masses could have crashed into the sun and then left lasting chemical traces,” says Yildiz. According to the models, this super-Earth would have been 5.6 times as heavy as Earth and rather low in lithium.

The simulations show that such a planet, as it spirals into the sun, remains intact long enough to sink below the sun’s convection zone. “As the planet sinks, some of its outer layers erode, but its core can survive,” the researcher explains. The planet’s core first stops in the denser layer of the sun below the convection zone and then gradually dissolves there. “There it creates an enrichment of heavy elements that changes the opacity and internal stratification of the sun,” says Yildiz.

Explanation for the discrepancies

“We did not expect that the model simulations for the different discrepancies would all point to a planet in the same mass range,” says Yildiz. “This was one of the most exciting results of our study.” The models showed that the lack of lithium on the sun’s surface could also be explained by the fall of a super-earth that weighs almost six Earth masses and is low in lithium into the sun.

According to Yildiz, these results support the idea that there was once a super-Earth near the Sun in the solar system that was swallowed up by our star. “Devouring such a super-Earth could help explain the differences between solar models and observations, including the solar internal structure and lithium deficiency,” says the astronomer.

Was there a super-Earth in the solar system?

Previous studies have already shown that a super-Earth may have formed in the Sun’s protoplanetary disk. This originated further out in the system, but then migrated further inwards due to gravitational turbulence. There it got into an unstable orbit that was too close to the sun and therefore crashed into our star.

However, Yildiz admits that his model study is not yet sufficient to prove the existence and end of such a super-Earth. However, future helioseismic analyzes of the Sun may reveal further evidence of such an event.

Source: Royal Astronomical Society; Mutlu Yildiz (Ege University, Izmir, Türkiye, Monthly Notices of the Royal Astronomical Society, 2026; doi: 10.1093/mnras/stag1527