本研究通过 Hubble Space Telescope 和 Swan Hill Observatory 观测证实长周期彗星 C/2021 A1 彗核已完全解体，排除了多种解体模型，指出由排气力矩驱动的旋转不稳定性是导致其灾难性破坏的最合理机制。
摘要：
我们呈现了解体中的长周期彗星 C/2021 A1 (Leonard) 的成像观测。Hubble Space Telescope 的高分辨率观测未显示存在残存碎片的证据，并将其可能的半径设定了 3 sigma 上限约为 60 m（假设反照率为 0.1）。相比之下，来自澳大利亚 Swan Hill Observatory 的宽视场观测显示了一片广阔的碎片云，其横截面和估计质量与 2021 年 12 月中旬（约 0.8 au 处）彗核完全解体相一致。两种方法得出解体前彗核半径为 r = 0.6+/-0.2 km。潮汐、碰撞、升华和压力约束爆炸模型对解体提供了不合理的解释。然而，由排气力矩驱动的旋转不稳定性在 C/2021 A1 彗核的轨道和尺寸下具有非常短的时间尺度（约 0.1 年），并为解体提供了最合理的机制。先前埋藏的挥发物的暴露和强烈升华加速了最初的旋转碎裂，导致彗核发生灾难性破坏。
英文摘要：
We present imaging observations of the disintegrating long-period comet C/2021 A1 (Leonard). High resolution observations with Hubble Space Telescope show no evidence for surviving fragments, and place a 3 sigma upper limit to their possible radius about 60 m (albedo 0.1 assumed). In contrast, wide field observations from the Swan Hill Observatory, Australia, show an extensive debris cloud, the cross-section and estimated mass of which are consistent with complete disintegration of the nucleus near mid- December 2021 (at about 0.8 au). Two methods give the pre-disruption nucleus radius, r = 0.6+/-0.2 km. Tidal, collisional, sublimation and pressure-confined explosion models provide implausible explanations of the disintegration. However, rotational instability driven by outgassing torques has a very short timescale (of order 0.1 year) given the orbit and size of the C/2021 A1 nucleus, and offers the most plausible mechanism for the disruption. Initial rotational breakup is accelerated by the exposure and strong sublimation of previously buried volatiles, leading to catastrophic destruction of the nucleus.
Long period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au on 2021 December 18 and may subsequently graze the planet with its dust trail less than two days later. We observed C/2021 A1 with the Lowell Discovery Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale Telescope on 2021 March 20, while the comet was inbound at heliocentric distances of r=4.97 au, 4.46 au, and 4.28 au, respectively. Tail morphology suggests that the dust is optically dominated by ~0.1-1 mm radius grains produced in the prior year. Neither narrowband imaging photometry nor spect…
Near-Sun Comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a 3-day {\it Hubble Space Telescope} (\hst) campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness, but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/…
Preperihelion Outbursts and Disintegration of Comet C/2017 S3 (Pan-STARRS)
一系列的事件，占主导地位的两个爆发和结束的近日点前解体的彗星C/2017 S3，检查。爆发的开始时间是由第二次爆发后核凝聚消失前的光变曲线确定的。虽然凝结的亮度急剧下降，但在STEREO-A的HI 1图像中，总亮度继续增长，直到近日点前两天。这些图像中测量到的红色星等是指投影面积为2200平方公里的均匀核碎片云，在第二次爆发时，它开始以76 m s^（-1）的速率膨胀。在一些STEREO-A图像中探测到的尾部延伸，由远离太阳释放的尘埃组成。对地面观测的轨道分析表明，这颗彗星是从奥尔特云沿引力轨道抵达的。治疗位置的残差作为一个分裂的彗星的同伴的偏移，我们确认存在的云的辐射压力驱动的毫米大小的尘埃颗粒从核在第二次爆发。我们探测到一个类似的，但紧凑和更微弱的云（或相当大的蓬松尘埃聚集碎片）在第一次爆发时释放。- -碎片将形成一个直径140米的球体，其动能相当于100吨无定形水冰释放的结晶热。对分裂彗星和1 I `Oumuamua的短命伴星的分支进行了讨论。
Comet C/2011 W3 (Lovejoy): Orbit Determination, Outbursts, Disintegration of Nucleus, Dust-Tail Morphology, and Relationship to New Cluster of Bright Sungrazers
Monitoring Volatile Evolution in Disrupting Comet D/2021 A1 (Leonard) with NOEMA and APEX
California Institute of Technology（加州理工学院）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Virginia Tech（弗吉尼亚理工大学）；American University（美国大学）；Institut de Radioastronomie Millimétrique（毫米波射电天文学研究所）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台、巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎西岱大学）
Dust and Volatiles in the Disintegrating Comet C/2019 Y4 (ATLAS)
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；University of Missouri（密苏里大学）；Universidad Diego Portales（迭戈帕托莱斯大学）；Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences（中国科学院南京天文光学技术研究所）
We identify a sample of 27 long-period comets for which both non-gravitational accelerations and Lyman-alpha based gas production rates are available. Seven of the 27 comets (i.e. 25 percent) did not survive perihelion because of nucleus fragmentation or complete disintegration. Empirically, the latter nuclei have the smallest gas production rates and the largest non-gravitational accelerations, which are both indicators of small size. Specifically, the disintegrating nuclei have a median radius of only 0.41 km, one quarter of the 1.60 km median radius of those surviving perihelion. The disint…
We present a study of C/2019 Y4 (ATLAS) using Sloan $gri$ observations from mid-January to early April 2020. During this timespan, the comet brightened with a growth in the effective cross-section of $\left(2.0 \pm 0.1 \right) \times 10^{2}$ m$^{2}$ s$^{-1}$ from the beginning to $\sim$70 d preperihelion in late March 2020, followed by a brightness fade and the comet gradually losing the central condensation. Meanwhile, the comet became progressively bluer, and was even bluer than the Sun ($g - r \approx 0.2$) when the brightness peaked, likely due to activation of subterranean fresh volatiles…
Major Outburst and Splitting of Long-Period Comet C/2015 ER61 (Pan-STARRS)
2017年4月初，在经过近日点的五周前，观测到缺乏尘埃的彗星C/2015 ER 61经历了一次大爆发，在此期间，其内在亮度短暂增加了约2 mag.本文提出的证据表明，耀斑很可能是产生伴核的核碎裂事件的产物，9个多星期后的6月11日，首次发现了这种病毒，并对其进行了19天的观察。发现伴星以小于1 m/s的速度从母核分离;随后它受到了14个单位的太阳引力加速度的非引力减速度。根据这个值，可以估计出伴星的总尺寸小于100米。与主核不同的是，伴星在时间尺度上表现出相当大的亮度波动，跨度至少有三个数量级，从一小时到几周不等。伴星的诞生和第一次探测之间的长时间间隔似乎是亮度变化的必然结果。来自光变曲线的证据表明，伴星之所以能够被探测到，只是因为它开始脱落大量的碎片，以及由于逐渐碎裂而新暴露的区域的活动增加，这一过程也导致伴星在6月底或7月初即将解体。
Meteor physics can provide new clues about the size, structure, and density of cometary disintegration products, establishing a bridge between different research fields. From meteor magnitude data we have estimated the mass distribution of meteoroids from different cometary streams by using the relation between the luminosity and the mass obtained by Verniani (1973). These mass distributions are in the range observed for dust particles released from comets 1P/Halley and 81P/Wild 2 as measured from spacecraft. From the derived mass distributions, we have integrated the incoming mass for the mos…
