The Sun may have swallowed a large rocky planet billions of years ago – and the traces of the lost world may still be hidden deep within it. This is shown by a new study.
Scientists have previously suggested that a “super-Earth” – a rocky planet several times more massive than Earth – may have fallen into the young Sun.
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The new research investigates whether such an event may have changed the Sun’s chemical composition and internal structure in ways that scientists can still detect today.
The findings have been published in the journal Monthly Notices of the Royal Astronomical Society.
“Our new study suggests that a planet several times more massive than Earth may have fallen into the young Sun, leaving a lasting chemical imprint deep within it,” says lead researcher Mutlu Yildiz, a professor at Ege University in Turkey.
The idea may help explain two long-standing mysteries about the sun.
Two unsolved puzzles
Scientists are using computer models to understand how stars form and change. But the standard models of the Sun don’t quite match their observations of the interior. In particular, they have trouble explaining the speed at which sound travels through an area just below the Sun’s outer convection zone. They also struggle to reproduce the exact depth of this zone, where hot material rises and cooler material sinks down.
The second mystery is about lithium. The sun’s surface contains much less lithium than scientists would normally expect. Because lithium is easily destroyed at high temperatures, its unusually low levels may reveal something important about the sun’s early history.
Yildiz and his colleagues wondered if these two riddles could have the same cause.
The planet may have changed the sun
Young stars are surrounded by discs of gas, dust, and rocky material from which planets form. Material can move between these discs and their stars. Because rocky planets have a different chemical composition than the surrounding gas, devouring a planet can change the composition of a young star.
The researchers used a computer program called MESA to simulate the sun’s evolution under different conditions. They tested what would happen if the young sun absorbed different amounts and types of material. Then, they compared the results with measurements of the sun’s internal and surface chemistry.
The models pointed to a scenario in which the Sun devoured a super-Earth with a mass of about five to ten times that of the Earth. This scenario helped explain both the Sun’s internal structure and its low lithium levels.
The calculations also suggested that a large rocky planet may have passed through the Sun’s outer layers while losing relatively little mass before reaching deeper areas. The material may therefore have left a lasting chemical and structural imprint.
Why do we lack super soils?
Astronomers have long wondered why many other planetary systems contain super-Earths, while our own Solar System has none. Previous research has suggested that such planets may have formed closer to the Sun than Mercury, before moving inward and disappearing into our star.
The new study does not prove that this has happened. But it does point to possible clues that the researchers can look for using measurements of vibrations moving through the sun.
If these predicted imprints are independently proven, they could provide strong evidence that our solar system once contained a large planet that disappeared inside the sun.
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