2024-03-27 ブラウン大学
This image was taken by NASA’s New Horizons spacecraft on Jan. 1, 2019 during a flyby of Kuiper Belt object 2014 MU69. Photo by NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
＜関連情報＞
- https://www.brown.edu/news/2024-03-27/space-snowman
- https://www.sciencedirect.com/science/article/abs/pii/S0019103524000861
486958アロコス内のCO氷とガスの保持 Retention of CO ice and gas within 486958 Arrokoth
Samuel P.D. Birch, Orkan M. Umurhan
Icarus Available online:2 March 2024
DOI:https://doi.org/10.1016/j.icarus.2024.116027
Highlights
•We developed a model for sublimation losses in cold Kuiper Belt Objects.
•Gas stays near vapor pressure equilibrium with a downward moving sublimation front.
•Large volumes of CO gas and ice can be sustained within KBOs for billions of years.
•Our work is testable with numerical models, and can aid future KBO observations.
Abstract
Kuiper Belt Objects (KBOs) represent some of the most ancient remnants of our solar system, having evaded significant thermal or evolutionary processing. This makes them important targets for exploration as they offer a unique opportunity to scrutinize materials that are remnants of the epoch of planet formation. Moreover, with recent and upcoming observations of KBOs, there is a growing interest in understanding the extent to which these objects can preserve their most primitive, hypervolatile ices. Here, we present a theoretical framework that revisits this issue for small, cold classical KBOs like Arrokoth. Our analytical approach is consistent with prior studies but assumes an extreme cold end-member thermophysical regime for Arrokoth, enabling us to capture the essential physics without computationally expensive simulations. Under reasonable assumptions for interior temperatures, thermal conductivities, and permeabilities, we demonstrate that Arrokoth can retain its original CO stock for Gyrs if it was assembled long after the decay of radionuclides. The sublimation of CO ice generates an effective CO ‘atmosphere’ within Arrokoth’s porous matrix, which remains in near vapor-pressure equilibrium with the ice layer just below, thereby limiting CO loss. According to our findings, Arrokoth expels no more than ≈1022 particles s−1, in agreement with upper limits inferred from New Horizons’ 2019 flyby observations. While our framework challenges recent predictions, it can serve as a benchmark for existing numerical models and be applied to future KBO observations from next-generation telescopes.
