Analytical constraints on ejectable dust agglomerate sizes from cometary nuclei during quiet sublimation
Year: 2026
Type: article
Abstract: Dust ejection from cometary nuclei controls cometary activity, yet the physical processes governing agglomerate detachment remain incompletely understood. We present an analytical approach for evaluating agglomerate detachment and subsequent transport under quiet sublimation conditions. Building on previous force-balance treatments, the formulation explicitly distinguishes between the condition required for initial detachment from the nucleus surface and that required for subsequent transport by sublimation-driven gas drag. This allows the lower and upper bounds of the ejectable agglomerate-size interval to be evaluated consistently by considering sublimation-driven gas drag, gravity, centrifugal force due to nucleus rotation, and size-dependent interparticle cohesion. The balance between sublimation-driven gas drag and cohesion provides a size-dependent criterion for the onset of dust detachment. The unresolved particle--surface contact geometry is parametrised by an effective cohesive contact-area factor that scales the reference size-dependent cohesive coupling. The results indicate that the balance between sublimation-driven gas drag and size-dependent cohesion is the primary control on the onset of dust detachment. At a heliocentric distance of 1.5 au, H_2O sublimation can detach agglomerates only when the effective cohesive contact between the agglomerate and the surrounding surface material is sufficiently small, whereas CO_2 and especially CO broaden the range of contact conditions under which detachment becomes possible. The predicted minimum and maximum ejectable agglomerate sizes overlap with the broad range of particle sizes reported or inferred from Rosetta observations, including the small porous particles detected by MIDAS and COSIMA and the larger agglomerates identified in the coma. Our approach therefore provides a physically transparent means of relating sublimation conditions and the mechanical properties of cometary surface material to the range of agglomerate sizes that can be released under quiet sublimation conditions. Because attenuation of the gas flux through a finite dry dust layer is not explicitly modelled, the calculated sublimation flux at the ice interface represents an upper-limit gas flux available for surface dust mobilisation, and the corresponding dust-detachment conditions represent favourable limiting conditions.
Source: Astronomy and Astrophysics
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7223158097