Linking ephemeris-derived outgassing forces to surface activity on comet Churyumov/Gerasimenko 67P: A comparative analysis of three post-Rosetta ephemerides

¹ State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, 129 Luoyu Road, Wuhan 430070, PR China
² Geodesy Observatory of Tahiti, University of French Polynesia, BP 6570, 98702 Faa’a, Tahiti, French Polynesia, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 3 February 2026
Accepted: 8 April 2026

Abstract

Context. The non-gravitational acceleration (NGA) of comet 67P/Churyumov-Gerasimenko, primarily driven by outgassing, exhibits pronounced anisotropy due to the nucleus’s highly irregular and strongly asymmetric shape. In the post-Rosetta era, several independent ephemerides have been reconstructed leveraging diverse NGA models and observational constraints.

Aims. We extracted and compared the NGA profiles from three independent post-Rosetta ephemerides to evaluate their dynamical consistency. By characterising the magnitude and orientation of these forces over a ±350-day window centred on the 2015 perihelion, we sought to link the ephemeris-derived acceleration to the heterogeneous surface activity observed during the Rosetta mission.

Methods. We first assessed the theoretical formulations of historical NGA models and characterised the reconstruction strategies of the three selected ephemerides. The effective NGA vectors were extracted by differentiating the Chebyshev interpolation polynomials of the trajectories under a unified DE440 planetary baseline. The resulting accelerations were decomposed into heliocentric RTN and nucleus-aligned SQP frames. Furthermore, we defined the ‘effective latitude’ of the acceleration to correlate the NGA with seasonal insolation geometry and surface activity distributions.

Results. We find that while the overall NGA magnitude is globally consistent across the three reconstructions, systematic discrepancies exist in their directional geometry. Specifically, the analysis of effective latitude reveals differences in capturing the hemispherical dominance, particularly regarding the intense southern hemisphere activity that persists after perihelion.

Conclusions. The persistent northern alignment of the effective NGA vector post-perihelion is driven by sustained southern hemisphere activity, consistent with in situ data. This signature reflects a spatially stable southern source that persists despite the gradual post-perihelion shift from H₂O to CO₂ dominance. We conclude that the nucleus-aligned SQP reference frame and effective latitude provide a physically interpretable framework to discriminate between different orbital solutions and link cometary dynamics to specific surface processes.