The interstellar traveller, 2I/Borisov, is the first clearly active extrasolar comet ever detected in our Solar System. We obtained high-resolution interferometric observations of 2I/Borisov with the Atacama Large Millimeter/submillimeter Array (ALMA) and multi-colour optical observations with the Very Large Telescope (VLT) to gain a comprehensive understanding of the dust properties of this comet. We found that the dust coma of 2I/Borisov consists of compact ‘pebbles’ of radii exceeding ~1 mm, suggesting that the dust particles have experienced compaction through mutual impacts during the bouncing collision phase in the protoplanetary disk. We derived a dust mass-loss rate of ≳200 kg s⁻¹ and a dust-to-gas ratio ≳3. Our long-term monitoring of 2I/Borisov with the VLT indicates a steady dust mass-loss with no significant dust fragmentation and/or sublimation occurring in the coma. We also detected emissions from carbon monoxide (CO) gas with ALMA and derived the gas production rate of Q(CO) = (3.3 ± 0.8) × 10²⁶ s⁻¹. We found that the CO/H₂O mixing ratio of 2I/Borisov changed drastically before and after perihelion, indicating the heterogeneity of the cometary nucleus, with components formed at different locations beyond the volatile snow-line with different chemical abundances. Our observations suggest that 2I/Borisov’s home system, much like our own system, experienced efficient radial mixing from the innermost parts of its protoplanetary disk to beyond the frost line of CO.

星际旅行者 2I/Borisov 是我们太阳系中发现的第一颗明显活跃的太阳系外彗星。我们使用阿塔卡马大毫米/亚毫米阵列 (ALMA) 获得了 2I/Borisov 的高分辨率干涉观测，并使用甚大望远镜 (VLT) 获得了多色光学观测，以全面了解这颗彗星的尘埃特性。我们发现 2I/Borisov 的尘埃彗发由半径超过约 1 毫米的致密“卵石”组成，这表明尘埃颗粒在原行星盘的弹跳碰撞阶段通过相互撞击而经历了压实。我们得出了≳ 200 kg s ^-1的粉尘质量损失率和粉尘气体比 ≳3. 我们用 VLT 对 2I/Borisov 的长期监测表明，尘埃质量稳定下降，在昏迷中没有发生明显的尘埃碎裂和/或升华。我们还用 ALMA 检测了一氧化碳 (CO) 气体的排放，并得出气体产率Q (CO) = (3.3 ± 0.8) × 10 ²⁶  s ^-1。我们发现 CO/H ₂2I/Borisov的O混合比在近日点前后发生了剧烈变化，表明彗核的异质性，组分形成于挥发性雪线以外的不同位置，具有不同的化学丰度。我们的观察表明，2I/鲍里索夫的主系统，就像我们自己的系统一样，从其原行星盘的最内部部分到二氧化碳的霜线以外都经历了有效的径向混合。