Combi M R, Mäkinen T, Bertaux J-L, Quémerais E, Ferron S, Coronel R
Dept. of Climate and Space Sciences and Engineering, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143.
Finnish Meteorological Institute, Box 503, SF-00101 Helsinki, FINLAND.
Astrophys J Lett. 2019 Oct 20;884(2). doi: 10.3847/2041-8213/ab4887.
The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliospheric Observer (SOHO) satellite observed the hydrogen coma of comet C/2017 S3 (PanSTARRS) for the last month of its activity from 2018 July 4 to August 4 and what appears to have been its final disintegration just 11 days before its perihelion on August 15. The hydrogen coma indicated water production had a small outburst on July 8 at a heliocentric distance of 1.1AU and then a much larger one on July 20 at 0.8 AU. Over the following two weeks the water production dropped by more than a factor of ten after which it was no longer detectable. The behavior is reminiscent of comet C/1999 S4 (LINEAR) in 2000, which had a few small outbursts on its inbound orbit and a major outburst at a heliocentric distance of about 0.8 AU, which was close to its perihelion, followed by its complete disintegration that was documented by several sets of observations including SWAN. C/2017 S3 (PanSTARRS) however had a much larger water production rate than C/1999 S4 (LINEAR). Here we estimate the size of the nucleus of C/2017 S3 just before its final outburst and apparent disintegration was estimated using the total amount of water produced during its last weeks for a range of values of the refractory/ice ratio in the nucleus. We also determine the size distribution of the disintegrating particles as the comet faded.
太阳和日球层观测台（SOHO）卫星上的太阳风各向异性（SWAN）全天氢莱曼α相机，在2018年7月4日至8月4日这颗彗星活动的最后一个月，观测到了C/2017 S3（泛星彗星）的氢彗发，以及在其8月15日近日点前11天似乎发生的最终解体。氢彗发显示，在7月8日，日心距离为1.1天文单位时，水的产生有一次小爆发，然后在7月20日，日心距离为0.8天文单位时，有一次大得多的爆发。在接下来的两周里，水的产生量下降了十倍以上，之后就再也检测不到了。这种行为让人想起2000年的C/1999 S4（LINEAR）彗星，它在进入轨道时有几次小爆发，在日心距离约0.8天文单位（接近其近日点）时有一次大爆发，随后完全解体，包括SWAN在内的几组观测记录了这一过程。然而，C/2017 S3（泛星彗星）的水产生率比C/1999 S4（LINEAR）彗星大得多。在这里，我们根据彗星最后几周产生的水的总量，针对彗核中难熔物质/冰的一系列比值，估算了C/2017 S3在其最后一次爆发和明显解体前彗核的大小。我们还确定了随着彗星亮度减弱，解体颗粒的大小分布。
