Secular orbital evolution of Jupiter family comets

¹ P.A.S. Space Research Centre, Bartycka 18A, 00-716 Warszawa, Poland
e-mail: wajer@cbk.waw.pl
² Dept. of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
³ IAPS-INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁴ IFAC-CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy
⁵ Département Lagrange, University of Nice – Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France

Received: 22 July 2016
Accepted: 16 November 2016

Abstract

Context. The issue of the long term dynamics of Jupiter family comets (JFCs) involves uncertain assumptions about the physical evolution and lifetimes of these comets. Contrary to what is often assumed, real effects of secular dynamics cannot be excluded and therefore merit investigation.

Aims. We use a random sample of late heavy bombardment cometary projectiles to study the long-term dynamics of JFCs by a Monte Carlo approach. In a steady-state picture of the Jupiter family, we investigate the orbital distribution of JFCs, including rarely visited domains like retrograde orbits or orbits within the outer parts of the asteroid main belt.

Methods. We integrate 100 000 objects over a maximum of 100 000 orbital revolutions including the Sun, a comet, and four giant planets. Considering the steady-state number of JFCs to be proportional to the total time spent in the respective orbital domain, we derive the capture rate based on observed JFCs with small perihelia and large nuclei. We consider a purely dynamical model and one where the nuclei are eroded by ice sublimation.

Results. The JFC inclination distribution is incompatible with our erosional model. This may imply that a new type of comet evolution model is necessary. Considering that comets may live for a long time, we show that JFCs can evolve into retrograde orbits as well as asteroidal orbits in the outer main belt or Cybele regions. The steady-state capture rate into the Jupiter family is consistent with ~1 × 10⁹ scattered disk objects with diameters D > 2 km.

Conclusions. Our excited scattered disk makes it difficult to explain the JFC inclination distribution, unless the physical evolution of JFCs is more intricate than assumed in standard, erosional models. Independent of this, the population size of the Jupiter family is consistent with a relatively low-mass scattered disk.