A new study suggests the young Sun may have engulfed a super- Earth (roughly 5- 10 times Earth’s mass) early in its history, potentially leaving lasting chemical and structural “fingerprints” deep inside that could still be detectable today.

The research, by Professor Mutlu Yildiz of Ege University in Türkiye and published in Monthly Notices of the Royal Astronomical Society (DOI: 10.1093/mnras/stag1527), uses stellar- evolution modeling (with the MESA code) to explore whether planetary engulfment could resolve long-standing mismatches between standard solar models and observations.

Key points from the work and related coverage:

Standard solar models struggle to simultaneously match helioseismic data (especially the sound- speed structure just below the convection zone and the convection zone’s depth) and the Sun’s strongly depleted surface lithium abundance.

The models that best fit multiple independent constraints involve the young Sun accreting a dense, rocky super- Earth. Preferred masses cluster around 5- 10 Earth masses (one standout model near ~5.6 Earth masses). The planet’s material, rich in heavy elements relative to the surrounding disk gas, could create a localized compositional gradient that alters opacity, temperature, density, and sound speeds.

Such a planet could largely survive passage through the outer layers while losing little mass, allowing its material to settle deeper and leave a lasting imprint.

This scenario also helps address why the Solar System lacks the super- Earths that are common around many other stars. Earlier theoretical work (Martin & Livio, 2016) had already suggested super- Earths could have formed inside Mercury’s orbit and migrated inward; the new study focuses on whether observable traces of engulfment could remain inside the Sun.

Yildiz notes that the calculations unexpectedly converged on a specific mass range and that the engulfment idea improves agreement with several observables at once. However, the study does not claim definitive proof, only that the scenario is physically plausible and that independent detection of the predicted structural/chemical signatures (via improved helioseismology or other methods) would provide strong supporting evidence.

The idea remains a hypothesis grounded in modeling rather than direct observation of residual planetary material.

Super- Earths are planets with masses between roughly 1 and 10 Earth masses (and radii typically ~1- 2 Earth radii). They are the most common type of planet detected around other stars (especially in close- in orbits), yet the Solar System has none. Their formation remains an active area of research, with several competing but complementary mechanisms.

Planet formation begins in a protoplanetary disk of gas and dust around a young star. Dust grains grow into pebbles, then planetesimals (~1- 100 km), and eventually planetary embryos. Super- Earth cores form primarily via core accretion:

• Solids accrete onto a rocky/icy core.
• Once the core reaches a few Earth masses, it can begin accreting a gaseous envelope (H/He) from the disk.
• Growth is limited by the local solid surface density (isolation mass) unless material is continuously supplied by radial drift or migration.

Many observed super- Earths are predominantly rocky (with thin or residual H/He atmospheres), though some may retain substantial water or gas envelopes (often called mini- Neptunes when radii are larger).

Main Formation Pathways

1. In Situ Formation (Close to the Star)
Planets grow near their final orbits (typically <1 AU) from a local reservoir of solids.

• Challenges: Standard minimum- mass solar nebula (MMSN) models lack enough solid material inside ~1 AU to build multiple super- Earths.
• Solutions: Enhanced solid surface densities (e.g., via pebble drift or a “dead zone” of low turbulence that allows material to pile up), or late assembly during disk dispersal when gas dynamical friction weakens, allowing embryos to collide and merge.
• Advantage: Explains compact, multi- planet systems with similar sizes within a system. Variations in the total solid mass available can produce the observed diversity across systems.

2. Formation Farther Out and Migration
Cores form beyond the snow line (where water ice is stable, typically several AU), grow more massive due to higher solid abundance, then migrate inward via Type- I disk torques.

• Embryos often pile up at the disk’s inner edge or in resonant chains.
• After the gas disk dissipates, dynamical instabilities can break the resonances, producing the non-resonant compact systems commonly observed.
• This pathway naturally produces a range of compositions (rocky if growth occurs mostly inside the snow line; water- rich if outside).

3. Ring/Planetesimal Concentration Models (Recent Emphasis)
Solids concentrate in narrow rings at sublimation lines (e.g., the silicate sublimation line near ~1 AU).

• Planetesimals form rapidly in these rings.
• Pairwise collisions grow planets until isolation or migration removes them from the ring.
• High- mass rings produce systems of similar- sized super- Earths; low- mass rings produce Solar-System- like terrestrial planets. This helps explain both the abundance of super- Earths and the intra-system similarity in sizes.

4. Pebble Accretion
Pebbles (cm- to- meter sized) drift inward and are efficiently accreted by embryos. Combined with migration, this can rapidly build multiple super- Earth- mass planets that end up near the star after resonant chains form and later destabilize.

Why No Super- Earths in the Solar System?

Several ideas address the Solar System’s uniqueness:

• Jupiter’s early formation may have acted as a barrier, blocking inward migration of outer material or preventing close- in super- Earth growth.
• Super- Earths could have formed inside Mercury’s orbit (especially in a low turbulence “dead zone” disk) and later migrated into the Sun, clearing the region of solids. This is the scenario explored by Martin & Livio (2016) and linked to the recent Yıldız (2026) solar- model work suggesting the young Sun may have engulfed a ~5- 10 Earth- mass body.
• Disk properties (turbulence level, solid mass, lifetime) simply differed from those of typical exoplanet-hosting disks.

Atmospheric Evolution

Even rocky- looking super- Earths often formed with primordial H/He envelopes. These can later be lost via:

• Photoevaporation (stellar XUV radiation)
• Core- powered mass loss
• Giant impacts

This produces the observed radius “valley” separating rocky super- Earths from gas- rich mini- Neptunes.

No single pathway explains everything. The leading picture combines elements of solid concentration (rings or pebble drift), core growth, limited gas accretion, and Type- I migration, followed by late dynamical sculpting. Key remaining puzzles include the exact fraction of water- rich vs. dry worlds, the role of disk turbulence/dead zones, and why the Solar System appears atypical.

Observations from Kepler, TESS, JWST atmospheric characterization, and future missions (e.g., PLATO, ARIEL) continue to refine these models by providing bulk densities, atmospheric compositions, and system architectures.

Planetary engulfment as a solution to solar-model discrepancies and its implications for planetary systems 

This is the full scientific paper behind the news coverage: “Planetary engulfment as a solution to solar-model discrepancies and its implications for planetary systems” by Mutlu Yıldız (Ege University, Türkiye).

Thousands of close-in exoplanets suggest planetary engulfment may be common. The author investigates whether early accretion of planetary material can resolve long- standing discrepancies between standard solar models and observations, specifically:

• Helioseismic sound-speed anomalies
• Convection-zone depth
• Surface abundances (including lithium)

Using the MESA stellar- evolution code, the models include pre- main- sequence accretion of metal- rich material (representing planetary engulfment) followed by metal-poor disc accretion (associated with planet formation).

Best- fitting model (DD1020) combines planetary engulfment with turbulent mixing and provides the strongest agreement with helioseismic constraints. It favors a super-Earth of mass ~5.6 Earth masses (≈0.33 Neptune masses), informally named “Dev Dilek.” Related best- fitting models prefer ~5- 10 Earth masses.

The dissolved planetary material settles below the convection zone (at mass coordinates m ≈ 0.96- 0.973 M⊙), creating a localized heavy- element enhancement (“Z-bump”). This modifies opacity and the internal stratification, improving the sound- speed profile.

Optimized control models that include variable mixing- length parameters and turbulent mixing without engulfment improve agreement only partially. Bayesian Information Criterion analysis indicates the improvement is not simply due to extra model flexibility.

Solar lithium depletion can be reproduced if the accreted material is lithium- poor and the planet mass is in the range 4.6- 5.8 Earth masses.

The paper also assesses physical feasibility via Roche- lobe stability, pressure- dependent planetary structure models, and classical aerodynamic drag/ablation. A compact rocky planet can traverse the solar convective envelope with negligible mass loss, supporting the scenario.

Main findings and conclusions

• Standard solar models systematically underpredict sound speed just below the convection zone and overpredict the convection- zone base radius. Surface metallicity and helium abundances are also difficult to match simultaneously.
• Planetary engulfment offers a unified physical mechanism that simultaneously improves multiple independent constraints.
• The heavy- element enhancement lies in a narrow layer beneath the convection zone (roughly r ≈ 0.67–0.7 R⊙ in the best models).
• Engulfment plus limited additional mixing beneath the convection zone can also account for the observed lithium depletion.
• The results strengthen the physical plausibility of early planetary engulfment in the Solar System and suggest it should be considered more broadly in models of planet- hosting stars, especially when precise asteroseismic data are available.

The paper does not claim definitive proof that the Sun swallowed a planet, only that the scenario is consistent with current data and provides a better match than standard models or alternative mixing prescriptions alone. Future independent detection of the predicted structural/chemical signature (via improved helioseismology or other probes) would strengthen the case.

This is the primary source that the RAS press release and subsequent popular- science articles (including the MSN piece) were based on. The full text is available via Oxford Academic (subscription or institutional access may be required for the complete PDF).

Published: Monthly Notices of the Royal Astronomical Society, Volume 551, Issue 4, October 2026,

DOI: 10.1093/mnras/stag1527

Author: Mutlu Yıldız

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   (0.33 ⁠) (Dev Dilek), while related best-fitting models favour –10 ⁠. The dissolved planetary material settles below the convection zone (⁠–0.973 ⁠), 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 ⁠. 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.