Sun May Have Swallowed a Super-Earth Planet in Its Infancy, Study Suggests

Our sun is a life-giving star, but it may also be a cosmic cannibal. New astronomical research indicates that our solar system’s primary energy source may have devoured a massive rocky world during its infancy according to findings published in Monthly Notices of the Royal Astronomical Society. While super-Earths are common occupants of other planetary systems, our solar system conspicuously lacks one. This violent planetary engulfment could explain why.

Mutlu Yildiz and Ege University Researchers Model the Early Solar System

The study was led by Mutlu Yildiz of Ege University, Turkey. Using advanced stellar evolution software and the MESA computer model for stellar evolution, Yildiz and his colleagues tested various scenarios of matter accretion by investigating different ways the sun could have swallowed a planet to see how the ingestion of a massive foreign body would alter a young star. Young stars like the sun during its infancy are surrounded by vast flattened clouds of gas and dust called protoplanetary discs, where substantial amounts of material can move between the disc and the star.

Since planets are made of material that is chemically different from the gas in the disc, we wondered whether the early engulfment of a planet could have left a chemical signature inside the young sun, Mutlu Yildiz said

The computer models converged on a very specific range. The calculations revealed that the best fit for the sun’s current characteristics involved the consumption of a planet between five and ten times the mass of the Earth, a type of planet called a super-Earth. 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, Professor Yildiz said. That was one of the most interesting outcomes of the study. This super-Earth managed to pierce the star’s outer layers, losing only a small portion of its mass before completely dissolving in the star’s interior.

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Solving Long-Standing Solar Anomalies and Missing Lithium

Standard physical models of stellar evolution have long struggled to account for observations. Astronomers explain that for many years, standard physical models of stellar evolution could not fully account for observations of seismic oscillations on the Sun. In particular, scientists recorded discrepancies in the speed of sound beneath the Sun’s convective zone and in the depth of the convective zone itself. At the same time, the mystery of the severe depletion of lithium on the star’s surface remained unresolved.

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Researchers suggested that both problems have a common origin in the Sun’s early chemical history. Since planets form from material that is chemically different from the gas in the protoplanetary disk, the absorption of a solid body should have left a noticeable trace.

“By modelling the sun’s evolution and comparing the results with precise observations of its interior, we find that the ingestion of a super-Earth could help explain long-standing differences between standard solar models and observations, including subtle changes in the sun’s internal structure and its depleted lithium abundance,” Yildiz said. We were interested in whether these problems might have a common origin in the early chemical history of the sun.

Migration Pathways and the Mystery of the Missing Super-Earths

The team’s research is supported by previous studies that suggest one or more super-Earth planets could have formed within the orbit of Mercury, the closest planet to the sun. These worlds would have then migrated through the protoplanetary disk surrounding the infant sun before crashing into the star. While earlier work proposed that a super-Earth could have formed and migrated into the young sun, the new paper asks whether the sun itself could still carry observable evidence that such an engulfment actually happened.

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Currently, this idea is based on computer modelling and unexplained solar features, but the researchers think that the predicted structural and chemical signature of a planetary engulfment could still exist within our star and could be detected. The next step is to see if these fingerprints can be independently detected, Yildiz concluded. At the same time, the new study leaves open the possibility that something else, other than this violent collision with the sun, may explain the discrepancies in measurements of the sun’s interior and its lithium content, as the team’s model doesn’t need a planet to have been totally engulfed by the sun.