Long-term gravitational spreading of irregular satellite families
Abstract
All four giant planets have the so-called irregular satellites. Residing on wide, eccentric and inclined orbits, these moons did not form in-situ but were captured from heliocentric orbits in the early solar system. Jupiter has the largest irregular moon population of more than 60, among which several orbital families are identified. Members of the same family are fragments of the same parent bodies during collisions. Himalia, the largest irregular moon at Jupiter (with a mass 10^{-9} of that of Jupiter), leads a prograde-revolving family. This family features a velocity dispersion of several 100s of m/s, well beyond that expected for family-creating collisions. Here we test if gravitational scattering by Himalia over the age of the solar system could explain the dispersion. We generate a synthetic Himalia family with an initial dispersion < 100 m/s, consistent with a collisional formation. This family is numerically propagated for 1 Gyr under the gravitational perturbation of Himalia. We observe that Himalia induces significant orbital spreading in the family especially in a. Extrapolating the dispersion over 4 Gyr we find that, while appreciable, it is not large enough to explain the observed orbital distribution of the family. Therefore, one must seek other explanations such as the disturbing action of planetary encounters during a solar system dynamical instability (Li & Christou 2017). In addition to spreading out the family, Himalia creates its own network of secular resonances where 90% of family members are captured into at least once over the course of our 1 Gyr simulation. This implies that members of the real family have been captured into such resonances in the past. Additionally, we estimate that Himalia has collisionally removed more than 60% of the smaller family members over the past 4 Gyr. Hence, the family likely had more members upon its formation. Finally, we have performed a similar exercise for Saturn's satellite Phoebe, seeking to test that satellite's ability to spread out a hypothetical family, possibly beyond recognition. The results of this investigation will be reported at the meeting.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5040712L