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

• Published in: Astronomy and astrophysics (Berlin) Vol. 694; p. A122
• Main Authors: Lim, Bumhoo, Ishiguro, Masateru
• Format: Journal Article
• Language: English
• Published: 07.02.2025
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202451002

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.