Sol May Have Swallowed One of Its Planets

[Recusant]

Our sun shows symptoms of minor indigestion, to put it a bit facetiously. There may even be the remnant of a relatively sizeable planet (about five times the mass of Earth) still inside.

"The Sun May Have Swallowed a Planet" | Universe Today

New research suggests that some unusual characteristics of the Sun may be explained if it swallowed a large planet sometime during the Solar System's formation.

Astrophysicists know quite a lot about the behaviour of stars, after centuries of observing and modelling them. We know how they form, what they're made of, even how they change as they evolve.

In recent decades, however, scientists have begun to notice a few things about our own star that are unusual. For one thing, the Sun's surface appears to be lithium-poor: excessively so. The proto-solar nebula from which the Sun formed billions of years ago is believed to have had two orders of magnitude more lithium than is currently seen in the Sun's outer shell. So where did all the lithium go?

A second oddity has to do with the speed of sound near the bottom of our star's convection zone. The convection zone is in the Sun's interior, just beneath the outermost layer. Here, heat is transported around via roiling plasma (as opposed to being transferred via radiation, which happens even deeper within). Astronomers are able to measure pressure waves rising up through the convection zone as they approach the surface. These 'helioseismic' measurements tell us about the Sun's bowels, just as seismic measurements on Earth tell us about the Earth's own interior indigestion. One bit of information scientists have gathered using these techniques is the speed of sound in different parts of the Sun's interior.

And here's the weird thing. The measured speed of sound near the bottom of the convection zone does not match our best models of what it should be. Something is off.

That's where this new paper, written by Mutlu Yildiz, Professor at Ege University in Turkey, comes in. He wondered whether both the lithium problem and the speed of sound problem might be solved by the presence of an engulfed planet stirring up the Sun's guts – the leftovers of a meal eaten eons ago.

"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," he told the Royal Astronomical Society.

[Continues . . .]

The paper is open access:

"Planetary engulfment as a solution to solar-model discrepancies and its implications for planetary systems" | Monthly Notices of the Royal Astronomical Society

Abstract:

Thousands of close-in exoplanets suggest that planetary engulfment may be common during stellar evolution. We investigate whether early accretion of planetary material can resolve discrepancies between standard solar models and observations, including helioseismic sound-speed anomalies, the convection-zone depth, and surface abundances.

Using MESA, we model pre-main-sequence accretion of metal-rich material representing planetary engulfment, followed by metal-poor disc accretion associated with planet formation. Model DD1020, combining planetary engulfment and turbulent mixing, provides the best agreement with helioseismic constraints. It favours a super-Earth of mass ~ 5.6 M_⊕ (0.33 M_N), while related best-fitting models favour ~ 5-10 M_⊕.

The dissolved planetary material settles below the convection zone (m = 0.96-0.973 M_⊙), producing a localized heavy-element enhancement that modifies opacity and internal stratification. Optimized control models with variable mixing-length parameters and turbulent mixing but without engulfment improve the agreement only partially. Bayesian Information Criterion analysis shows that the improvement cannot be explained solely by increased model flexibility. The observed solar lithium depletion can be reproduced if the accreted material is lithium-poor and the engulfed planet has a mass of 4.6–5.8 M_⊕.

We also assess the physical feasibility of engulfment using Roche lobe stability, pressure-dependent planetary structure models, and classical aerodynamic drag and ablation. A compact rocky planet can traverse the solar convective envelope with negligible mass-loss, providing independent support for the proposed scenario.

[Dark Lightning]

I saw that at Science Daily. The more we learn, the weirder the universe gets. Who would have thought of something like this? Though in all fairness we know that black holes will eat anything.