Statistical Study On Dynamic Characteristics Of Long-period Comets

Long period comet(LPC)preserves the original material of the early solar system.The study of their dynamics is the frontier of current research on small bodies in the solar system.Through the study of LPC,we can deepen the understanding of the evolution of LPC orbit,deeply understand the early history of the solar system,further explore the structure of the oort cloud,and provide relevant research data for spacecraft to detect LPC.In this paper,we investigate the dynamic characteristics of LPC based on the latest and most complete LPC observations recorded by JPL(Jet Propulsion Laboratory)and MPC(Minor Planet Center)from 1800 to April 2021.It includes three aspects:(1)The orbital characteristics are analyzed statistically based on the observed data.After the definition of all kinds of comets is clarified,a reasonable SAMPLE set of LPC is obtained,and the original orbit of LPC is obtained by backward integration.The distribution difference between observation orbit and original orbit 1/a and q is compared and analyzed,and the difference between Oort Cloud Comet and other LPC is compared;(2)The orbit characteristics of LPC are studied based on numerical simulation.LPC test particles were obtained by using a simplified numerical model,and the simulation results were compared with the observed data;(3)Explore the feasibility of LPC insitu detection.According to the LPC observation data,the distribution characteristics of comets at perihelion,perigee and true perigee angles are obtained,and the favorable conditions for LPC in-situ detection are analyzed.The main conclusions we draw are:(1)There is a significant difference in the distribution of the reciprocal of the semi-major axis between the LPC observation orbit and the original orbit,with the peak position at(1/a)obs～2×10-5 au-1 and(1/a)ori～6×10-5 au-1,respectively;(2)If LPC are divided into large perihelion(q>3.1 au)and small perihelion(q ≤3.1 au)by 3.1 au,the peak position on the reciprocal of the semi-major axis of the comet’s original orbit is the same;(3)There is no significant difference between JPL and MPC data,but JPL provides more comprehensive information;(4)When comparing oort cloud comet with other LPC,it is found that oort cloud comet generally have large perihelion distances(more than 50%oort cloud comets with q>3.1 au);(5)After comparing the LPC test particles with the observed data,it is found that the observed LPC only account for a small part of the total number of LPC due to the selective effect of observation;(6)When using spacecraft to detect LPC,the best encounter conditions are that the close distance of LPC is less than 2 au,the true anomaly is smaller,and they are located near the perihelion.These results provide important information for us to understand the dynamic characteristics of LPC and oort cloud comet,and will also provide a research basis for the selection of LPC as the target of future space missions.