文章基本信息

标题：Cometary Activity Begins at Kuiper Belt Distances: Evidence from C/2017 K2
本地全文：下载
作者：David Jewitt ; Yoonyoung Kim ; Max Mutchler 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2021
卷号：161
期号：4
页码：1-11
DOI：10.3847/1538-3881/abe4cf
语种：English
出版社：American Institute of Physics
摘要：We study the development of activity in the incoming long-period comet C/2017 K2 over the heliocentric distance range 9 ≲ rH ≲ 16 au. The comet continues to be characterized by a coma of submillimeter-sized and larger particles ejected at low velocity. In a fixed co-moving volume around the nucleus we find that the scattering cross section of the coma, C, is related to the heliocentric distance by a power law, , with heliocentric index s = 1.14 ± 0.05. This dependence is significantly weaker than the rH−2 variation of the insolation as a result of two effects. These are, first, the heliocentric dependence of the dust velocity and, second, a lag effect due to very slow-moving particles ejected long before the observations were taken. A Monte Carlo model of the photometry shows that dust production beginning at rH ∼ 35 au is needed to match the measured heliocentric index, with only a slight dependence on the particle size distribution. Mass-loss rates in dust at 10 au are of order 103 kg s−1, while loss rates in gas may be much smaller, depending on the unknown dust to gas ratio. Consequently, the ratio of the nongravitational acceleration to the local solar gravity, α', may, depending on the nucleus size, attain values of ∼10−7 ≲ α' ≲ 10−5, comparable to values found in short-period comets at much smaller distances. Nongravitational acceleration in C/2017 K2 and similarly distant comets, while presently unmeasured, may limit the accuracy with which we can infer the properties of the Oort cloud from the orbits of long-period comets.