A Collisional Origin for Ice-rich Iapetus and Titan's Anomalous Eccentricity
Abstract
We test whether collisions involving Titan can eject enough water-rich material onto sufficiently distant Saturn-bound orbits to form Iapetus, while also accounting for Titan's orbital eccentricity. Three-dimensional impact calculations and post-impact trajectories examine initially Saturn-unbound and bound impactors. In the oblique unbound case with a differentiated impactor roughly a tenth the mass of Titan at a speed of 10 km s−1, outgoing predominantly icy material from a selected population totaling about 3.5 times Iapetus's mass remains Saturn-bound for days after impact. We track an icy sample whose orbital apoapsis extends beyond Iapetus's distance. After impact, Titan's eccentricity increases to near 0.13, while the impactor's rocky core escapes Saturn. In another case, a bound companion one quarter Titan's mass collides at 45∘ and about 3.7 km s−1, ejecting 0.60 Iapetus masses of ice. The rocky impactor core initially skips past Titan; an orbital continuation reaches return contact after 6.9 yr. This run also retains 0.48 Iapetus masses of ice. Titan's eccentricity evolves due to the initial impact and debris scattering. The merger results in a Titan with an eccentricity of about 0.10. These results establish the collisional production of an icy debris reservoir, with some material on orbits of large semimajor axis; raising Iapetus's periapse would require gas drag or dynamical friction.
Related
- The geometric origin of the thermal eccentricity law
- The geometric origin of the thermal eccentricity law
- Evidence for orbital eccentricity supports a hierarchical origin for GW231123
- Planetesimal Delivery to Giant Planet Circumplanetary Disks: Bulk Ice Enrichment and an Ice-rich Iapetus
- Collisional excitation of H_2CO by He. Experimental validation of state-of-the-art scattering calculations
BibTeX
@misc{mosqueira2026collisional,
title = {{A Collisional Origin for Ice-rich Iapetus and Titan's Anomalous Eccentricity}},
author = {Ignacio Mosqueira},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28948},
eprint = {2609.28948},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28948},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A Collisional Origin for Ice-rich Iapetus and Titan's Anomalous Eccentricity
AU - Ignacio Mosqueira
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.28948
UR - https://arxiv.org/abs/2609.28948
AB - We test whether collisions involving Titan can eject enough water-rich material onto sufficiently distant Saturn-bound orbits to form Iapetus, while also accounting for Titan's orbital eccentricity. Three-dimensional impact calculations and post-impact trajectories examine initially Saturn-unbound and bound impactors. In the oblique unbound case with a differentiated impactor roughly a tenth the mass of Titan at a speed of 10 km s^−1, outgoing predominantly icy material from a selected population totaling about 3.5 times Iapetus's mass remains Saturn-bound for days after impact. We track an icy sample whose orbital apoapsis extends beyond Iapetus's distance. After impact, Titan's eccentricity increases to near 0.13, while the impactor's rocky core escapes Saturn. In another case, a bound companion one quarter Titan's mass collides at 45^∘ and about 3.7 km s^−1, ejecting 0.60 Iapetus masses of ice. The rocky impactor core initially skips past Titan; an orbital continuation reaches return contact after 6.9 yr. This run also retains 0.48 Iapetus masses of ice. Titan's eccentricity evolves due to the initial impact and debris scattering. The merger results in a Titan with an eccentricity of about 0.10. These results establish the collisional production of an icy debris reservoir, with some material on orbits of large semimajor axis; raising Iapetus's periapse would require gas drag or dynamical friction.
ER -