Billions of years ago, the Sun may have consumed a planet, and scientists believe the proof is still hiding within it. Published in Monthly Notices of the Royal Astronomical Society, a new study suggests that a super-Earth-sized world plunged into the young Sun, leaving a permanent chemical signature beneath its surface. These traces are what the researchers refer to as “fingerprints.”.
The idea is simple: a planet several times more massive than Earth entered the Sun and broke apart, mixing its material into the star’s interior. That mixing changed the Sun’s composition in ways that can now be measured. The study was led by Professor Mutlu Yildiz of Ege University in Turkey.
“Our new study suggests that a planet several times more massive than Earth may have fallen into the young Sun and left a lasting chemical imprint deep inside it.”
What the Fingerprints Show
Yildiz and his team modelled the Sun’s entire history using the MESA stellar-evolution code. They then compared those models against precise observations of the Sun’s interior, including its sound-speed structure and its lithium abundance. The comparison revealed a pattern.
For decades, the accepted physics of how stars age has failed to account for certain readings of the Sun’s inner movements at once. Two particular measurements have proven especially difficult to reconcile with models: the rate at which sound moves through the material beneath the Sun’s outer layer of moving gas, and the depth of that very layer itself. Meanwhile, the Sun displays a marked reduction of lithium on its visible surface, something already widely recognized.
The researchers speculated that both puzzles may trace back to the same moment in the Sun’s chemical past. When young stars form, they gather protoplanetary discs around them, and large quantities of matter pass between those discs and the stars themselves. The material that makes up planets differs chemically from the gas found within the disc. The question then became whether the early swallowing of a planet could leave a chemical mark inside the young Sun.
The simulations pointed to a situation where the youthful Sun consumed a super-Earth weighing somewhere between 5 and 10 times the mass of Earth. The models produced that mass range as a result, not as an initial premise that had been entered into them.
The MESA Code and the Test
MESA is a simulation code built for studying how stars change over time, and the scientists employed it to examine various histories of mass added from outside, comparing the outcomes against measurements made by looking at the Sun’s interior and the makeup of its outer layer. They also put other possible causes to the test, including the way matter behaves under pressure, how light moves through the material, and different ways of describing how heat and gas move within the star.
Among the findings, the research pointed to a particular mass range for super-Earths, and that outcome stood out as one of the most intriguing parts of the work.
Several independent measurements of the Sun’s properties, including observations of its interior and its unusually low lithium abundance, are all matched at once by the modelling.
Why the Sun Has Low Lithium
A noticeable reduction in lithium can be seen on the Sun’s surface, and this has become widely recognized. Standard models have found it difficult to explain why this reduction occurs.
The team’s scenario is that a super-Earth migrated inward through the gas disc that surrounded the young Sun, eventually falling into the star. As it broke apart, its material mixed with the Sun’s interior. That mixing could have altered the Sun’s internal structure and reduced its lithium abundance.
The researchers discovered that a planet could pass through the Sun’s outer layers without losing much mass. This suggests that planets might leave lasting traces within their host stars long after they have vanished.
What Happens Next
While the team acknowledges that proof may be beyond reach, they say it might not be possible to definitively establish that the Sun swallowed a planet. Still, they argue that identifying the predicted structural and chemical signature independently, perhaps through helioseismic or other methods, would give strong support to the idea that such an event took place billions of years ago.
What follows is a test to determine whether these fingerprints can be detected on their own.
The Missing Super-Earths
Our own solar system lacks any super-Earths, even though many other star systems contain such planets. A new study refers back to prior work that indicates one or more super-Earths might have formed within the orbit of Mercury, then moved inward through the gas disc, possibly plunging into the young Sun along the way.
The prior research laid out a route for a planet to be consumed but made no demand that the star eventually took it in. This new investigation instead inquires whether the Sun might still bear signs that such an engulfment actually occurred, and the researchers believe it can.
The Image and the Credit
A picture of a star swallowing a planet appears within the paper, along with a blue line that shows how the planet moves closer to the star before crashing into it. The credit for the image belongs to NASA, ESA, CSA, and Ralf Crawford (STScI).
The Paper and the Publication
The Monthly Notices of the Royal Astronomical Society carries the full paper, titled “Planetary engulfment as a solution to solar-model discrepancies and its implications for planetary systems,” with the DOI 10.1093/mnras/stag1527.
Founded in 1820, the Royal Astronomical Society (RAS) works to encourage and promote the study of astronomy, solar-system science, geophysics and closely related fields of science. It has more than 4,000 Fellows, with a third of them living abroad, including scientific researchers in universities, observatories and laboratories alongside historians of astronomy and other members.
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| Stage | Detail |
|---|---|
| Early history | Young Sun surrounded by a protoplanetary disc |
| Migration | Super-Earth forms inside Mercury’s orbit, moves inward |
| Collision | Planet falls into the Sun |
| Mixing | Material mixes with the Sun’s interior |
| Observations | Helioseismic data and surface lithium abundance |
| Models | MESA code tests different accretion histories |
| Results | Converge on a 5–10 Earth-mass planet |
The researchers’ findings are limited in scope. They intend to put their working idea to the test again. It is still unknown whether the telltale signs can be detected.
The team’s hope is that future observations will confirm their prediction.
What is remarkable is the very notion: that our own familiar Sun could bear the trace of a world that once existed and then vanished. If such evidence does exist, it is sealed within the star itself, awaiting the proper instrument to reveal it.