发表机构
Southwest Research Institute; University of Maryland, College Park; NASA Goddard Space Flight Center; Catholic University of America; Auburn University; Universität Bern（西南研究院; 马里兰大学帕克分校; 美国宇航局戈达德太空飞行中心; 美利坚天主教大学; 奥本大学; 伯尔尼大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
JWST观测星际彗星3I/ATLAS，发现其富含耐火材料的水冰聚集体，连接了太阳系彗发与海王星外天体，表明原行星盘冰颗粒性质存在连续谱。
AI 中文摘要
我们展示了2025年8月6日（第1历元）、2025年12月22日（第2历元）和2026年4月1日（第3历元）获得的星际彗星3I/ATLAS的JWST/NIRSpec PRISM观测结果，这些观测跨越了近日点前后八个月，对应的日心距离分别为3.3、2.4和5.7天文单位。光谱揭示了宽的3微米吸收带以及H$_2$O、CO$_2$和CO气体发射。与先前报道的富含水冰的太阳系彗发不同，强的3微米吸收伴随着微弱或缺失的1.5和2.0微米水冰带。光谱建模表明，观测结果最好由包含耐火材料的亚微米至微米大小的含水冰聚集体再现。与第1历元相比，第3历元的光谱倾向于存在第二类更大的、微米大小的、富含冰的聚集体，并在3.1微米附近表现出微妙的类似菲涅耳的结构，与结晶水冰一致。这些观测可以通过两种方式解释：两个历元均为结晶水冰，光谱演化主要源于颗粒大小和耐火材料混合的变化；或者从类似无定形状态向结晶状态的演化。3I的光谱特性介于含冰的太阳系彗发和几类中等大小的海王星外天体之间，表明在不同原行星盘中形成的星子冰构建块可能在水冰的物理状态上呈现连续谱，范围从纯冰颗粒到在亚微米至微米尺度上具有不同耐火材料含量的含水冰聚集体，而3I延伸至该连续谱的富含耐火材料端。
英文摘要
We present JWST/NIRSpec PRISM observations of the interstellar comet 3I/ATLAS obtained on 2025 August 6 (Epoch 1), 2025 December 22 (Epoch 2), and 2026 April 1 (Epoch 3), spanning eight months around perihelion at heliocentric distances of 3.3, 2.4, and 5.7 au, respectively. The spectra reveal a broad 3 $μ$m absorption band together with H$_2$O, CO$_2$, and CO gas emission. Unlike previously reported water-ice-rich Solar System comae, the strong 3 $μ$m absorption is accompanied by weak or absent 1.5 and 2.0 $μ$m water-ice bands. Spectral modeling indicates that the observations are best reproduced by submicron- to micron-sized water-ice-bearing aggregates containing refractory material. Compared with Epoch 1, the Epoch 3 spectrum favors the presence of a second population of larger, micron-sized, ice-rich aggregates and exhibits a subtle Fresnel-like structure near 3.1 $μ$m, consistent with crystalline water ice. The observations can be explained by either crystalline water ice at both epochs, with the spectral evolution arising primarily from changes in grain size and refractory mixing, or an evolution from an amorphous-like to crystalline state. The spectral properties of 3I bridge those of water-ice-bearing Solar System comae and several spectral classes of mid-sized trans-Neptunian objects, suggesting that the icy building blocks of planetesimals formed in different protoplanetary disks may span a continuum in the physical state of water ice, ranging from pure ice grains to water-ice-bearing aggregates with varying refractory content at submicron-to-micron scales, with 3I extending toward the refractory-rich end of this continuum.
Comments22 pages, 10 figures, 2 tables. Accepted for publication in The Astrophysical Journal Letters
