Аңдатпа
Thermal stresses in small bodies approaching the SunModern agglomeration models describe cometary nuclei as porous bodies with lowdensities ( 0.1 g/cm³), yet observations of comets Halley and Shoemaker–Levy 9 indi-cate significantly higher densities ( 0.6 g/cm³), suggesting a need to revise these models.Thermal stress has emerged as a plausible mechanism for fragmentation, capable of op-erating far from the Sun and without requiring tidal forces. Studies (Tauber and Kuhrt,1987; Shestakova and Tambovtseva, 1997; Tambovtseva and Shestakova, 1999; ˇCapekand Vokrouhlick´y, 2010) show that thermal stresses can exceed the tensile strength ofterrestrial materials.This mechanism is also relevant to the origin of meteorites and near-Earth ob-jects (NEOs). Research (Broˇz, M. et al., 2024) highlights the role of asteroid familieslike Karin, Koronis, and Massalia in generating NEOs and ordinary chondrites. Car-bonaceous chondrites are linked to bodies such as 3200 Phaethon, which may undergothermal disruption near the Sun.We apply both analytical and numerical solutions of the heat diffusion equationwith one initial and two boundary conditions (Shestakova and Tambovtseva, 1997).The analytical approach assumes constant thermal diffusivity and is restricted to ide-alized parabolic orbits with zero perihelion, whereas the numerical model accountsfor temperature-dependent thermal diffusivity and realistic orbital configurations withnon-zero perihelion distance.Spherical bodies made of crystalline ice, basalt, and chondrites are modeled alongparabolic orbits. Initial uniform temperatures are set at Tbb ≈ 150 K (3.45 AU) forsilicates and Tbb ≈ 30 K (86 AU) for ice, with final distances of 0.0345 AU (Tbb ≈1500 K) and 4.95 AU (Tbb ≈ 125 K), respectively. Results show rapid internal heatingfor small bodies, while larger ones retain cold interiors (see Fig. 1).Comparison with strength lines (see Fig. 2) suggests that bodies with radii of 30 mto 5 km may undergo fragmentation, even at distances from 10 AU to 40 AU.Smallerfragments (with radii less than 30 meters) are unlikely to undergo thermal destruc-tion, as they experience nearly uniform heating throughout their volume, resulting innegligible internal temperature gradients and stress accumulation. Nevertheless, suchbodies are subject to active sublimation(Shestakova and Serebryanskiy, 2023) as theyapproach the Sun. In contrast, larger nuclei (more than 1 km) retain a cooler interior and exhibit critical thermal stresses in the near-surface layers, which is consistent withthe observed onset of coma formation during solar approach. The breakup of cometShoemaker–Levy 9 was likely initiated by this mechanism, with thermal fracturingpossibly preceding the tidal disruption (Shestakova et al., 2025).According to Fig. 3, destructive internal stresses arise in basaltic, carbonaceous, andordinary chondritic bodies at heliocentric distances of approximately 2.5 AU, 2 AU,and 1 AU, respectively. These stresses affect bodies with radii not exceeding 10 meters,whose fragmentation is unlikely to produce observable dust clouds unless they passclose to Earth such as ordinary chondrites with radii around 10 m. Near Earth’sorbit, carbonaceous chondrites (40 m) and basaltic bodies (80 m) may also undergofragmentation ( ˇCapek and Vokrouhlick´y, 2010).Larger objects tend to break up closerto the Sun, initiating a cascade of fragmentation. The resulting smaller fragmentscontinue to disintegrate, forming clouds of fine dust that may reach the sublimationzone and become detectable via optical or infrared observations.Figure 1: Temperature profiles from the center (x/r = 0) to the surface (x/r = 1) insidebodies of various sizes at the final heliocentric distances of 0.0345 AU (7.42 R⊙) and 4.95 AU,for chondritic material (left) and crystalline ice (right), respectively.Figure 2: Thermal stresses at the center (x/r → 0, left) for the radial component and at thesurface (x/r = 1, right) for the tangential component, computed analytical and numerical atvarious heliocentric distances from the initial position at 86 AU to the final point at 4.95 AUfor ice bodies.Figure 3: Thermal stresses at the center (x/r → 0, left) for the radial component andat the surface (x/r = 1, right) for the tangential component, computed analytically andnumerically at various heliocentric distances from the initial position at 3.45 AU to the finalpoint at 0.0345 AU (≈ 7.42 R⊙) for chondritic and basalt bodies.ReferencesBroˇz, M., Vernazza, P., Marsset, M., Binzel, R. 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