Enlargement of depressions on comet 81P/Wild 2: Constraints based on 30-year cometary activity in the inner Solar System

¹ Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
² SNU Astronomy Research Center, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

^★ Corresponding authors; bumhoo7@snu.ac.kr; ishiguro@snu.ac.kr

Received: 5 June 2024
Accepted: 9 December 2024

Abstract

Context. The Stardust flyby mission to Jupiter-family comet (JFC) 81P/Wild 2 (hereafter, 81P) captured its dense quasicircular depressions. The formation mechanism behind these depressions remains a subject of debate.

Aims. We aim to study how cometary activity contributed to the formation and enlargement of these depressions by analyzing Stardust flyby images and ground-based observation data.

Methods. We calculated the time-dependent water production rate of 81P inside the snow line (<3 au) and compared it with the observational data. In addition, we estimated the fallback debris mass using an observation-based model, where a dust ejection from 81P was considered to reproduce ground-based observations of the dust tail. We compared the total excavated volume of water and dust with the total depression volume derived, using the 81P shape model.

Results. We find that the total excavated volume after 81P was injected into the inner Solar System accounts for up to only 30% of the depression volume. This suggests that a large portion (>70%) of the depressions had already existed before the comet was injected into the current orbit. In addition, we estimated the dust-to-ice mass ratio for 81P to be 2–14.

Conclusions. We suggest that most depressions observed for 81P were formed in their source regions.