发表机构
Physical Research Laboratory; Indian Institute of Technology, Gandhinagar（物理研究实验室; 甘地纳加尔印度理工学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
研究星际彗星3I/ATLAS甲烷延迟探测，通过热物理模型结合银河宇宙射线加工，发现深层水冰捕获甲烷在近日点后释放，并约束其星际暴露年龄为0.87-3.1 Gyr。
AI 中文摘要
星际彗星 3I/ATLAS 表现出不寻常的挥发性活动，包括强烈的 H$_2$O、CO 和 CO$_2$ 产生，以及近日点后 CH$_4$ 的延迟探测。在本工作中，我们利用形状模型结合考虑了银河宇宙射线星际加工的热物理核模型，研究了 H$_2$O、CO$_2$ 和 CO 冰基质中 CH$_4$ 的延迟探测。我们追踪了这些挥发物随日心距离的升华、捕获、消耗和释放过程，并通过 12000 次模型运行探索了相关参数空间，以确定能够重现这些挥发物观测产生率的原始挥发物储库和有效银河宇宙射线暴露年龄的可行组合。可行的模型倾向于一个富含挥发物的原始储库，与在 CO 雪线之外超低温（$T < 20$ K）区域的形成一致，随后在星际穿越期间经历了 0.87--3.1 Gyr 的有效银河宇宙射线加工暴露。银河宇宙射线加工产生了连续的成分梯度，并将部分 CO 储库转化为次生 CO$_2$，同时通过辐射分解转化消耗了近表面 CH$_4$。CH$_4$ 的延迟探测可以通过更深层 H$_2$O 基质中捕获的 CH$_4$ 的存留，以及近日点后次表层加热推进时的后续释放来解释。CH$_4$ 升华的时间可用于估算 3I/ATLAS 的有效银河宇宙射线加工年龄。后验分布还揭示了原始尘埃含量与银河宇宙射线暴露之间的简并性，其中富尘埃、弱加工和富冰、强辐照的演化路径产生了具有相似热物理性质的加工次表层。
英文摘要
Interstellar comet 3I/ATLAS shows unusual volatile activity, including strong H$_2$O, CO, and CO$_2$ production and a delayed post-perihelion detection of CH$_4$. In this work, we investigate the delayed CH$_4$ detection in an H$_2$O, CO$_2$, and CO ice matrix using a shape model coupled with a thermophysical nucleus model that incorporates interstellar processing by Galactic Cosmic Rays. We track the sublimation, trapping, depletion, and release of these volatiles as a function of heliocentric distance and explore the relevant parameter space through 12000 model runs to identify viable combinations of primordial volatile inventory and effective GCR exposure age that reproduce the observed production rates of these volatiles. The viable models favour a volatile-rich primordial inventory consistent with formation in an ultra-cold ($T < 20$ K) region beyond the CO snowline, followed by an effective GCR processing exposure of 0.87--3.1 Gyr during interstellar passage. GCR processing produces a continuous compositional gradient and converts part of the CO reservoir into secondary CO$_2$ and depletes near-surface CH$_4$ through radiolytic conversion. The delayed CH$_4$ detection can be explained by the survival of CH$_4$ trapped within the deeper H$_2$O matrix and its subsequent release as subsurface heating progresses after perihelion. The timing of CH$_4$ sublimation can be used to estimate the effective GCR processing age of 3I/ATLAS. The posterior distributions also reveal a degeneracy between primordial dust content and GCR exposure, where dust-rich, weakly processed and ice-rich, strongly irradiated evolutionary pathways produce processed subsurface layers with similar thermophysical properties.
CommentsAccepted for publication in ApJ (total 22 pagesand 8 figures, including appendix)
