Split Comets and the Circumstances of Splitting for Four Comets

Yu. A. Chernetenko

Transactions of IAA RAS, issue 51, 93—107 (2019)

DOI: 10.32876/ApplAstron.51.93-107

Keywords: comets, split comets, nongravitational acceleration, 101P comet, 213P comet, P/2013 R3 comet, P/2016 J1 comet

Abstract

The circumstances of splitting comets are mainly studied by the method proposed by Z. Sekanina. It is based on the positions of the fragment relative to the comet nucleus as obtained from positional observations of these bodies. Then, the date of separation, the relative velocity and the relative radial component of the fragment nongravitational acceleration are determined by the least squares method (LSM). There are also some other ways to study this phenomenon. The paper presents an other approach to studing split comets. In the obtained orbit of a comet, moments of separation are assigned at a certain interval. It is assumed that the coordinates of each of these points are also common for the fragment itself. Then, the components of the fragment velocity and the parameters of nongravitational acceleration due to Marsden’s model are determined by the LSM from the positional observations of the fragment. Errors of the comet orbit parameters are not taken into account. The smallest RMS value of the fragment observations, obtained as a result of the split time variation, determines the date of splitting. For this date, the components of the relative velocity of the fragment ($V_{rel}$), and the angle between the vector of this velocity and the direction to the Sun ($U_3$) are determined. The circumstances of splitting the 101P, 213P, P/2013 R3, P/2016 J1 comets are considered. The relative separation velocities in the range $0.4–4 m·s^{-1}$ were obtained. For the first three comets, the relative velocity vectors of the fragment form 2º to 40º angles with the direction to the Sun. These results can be interpre- ted to mean that the fragmentation can be caused by uneven heating of the comet’s nucleus (thermal stress). For P/2016 J1, relative velocities are less than $1 m·s^{-1}$, which may be due to rotational instability of the original cometary nucleus. For the fragments of the 101P and P/2016 J1 comets, the estimations obtained are consistent with the results of other authors. The method suggested for studying the circumstances of the separation of comets can be used along with other methods. This approach can be improved if we consider integration of the comet equations of motion together with those of the fragmens. In this case, coordinates at the time of separation can be evaluated using the observations of both bodies, and the velocities and nongravitational parameters – according to the observations of each of the bodies considered.

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