On collisional capture rates of irregular satellites around the gas-giant planets and the minimum mass of the solar nebula

Abstract

We investigate the probability that an inelastic collision of planetesimals within the Hill sphere of the Jovian planets could explain the presence and orbits of observed irregular satellites. Capture of satellites via this mechanism is highly dependent on not only the mass of the protoplanetary disc, but also the shape of the planetesimal size distribution. We performed 2000 simulations for integrated time intervals ∼2 Myr and found that, given the currently accepted value for the minimum mass solar nebula and planetesimal number density based upon the Nesvorný et al. and Charnoz & Morbidelli size distribution dN∼D−3.5dD, the collision rates for the different Jovian planets range between ∼0.6 and ≳170 Myr−1 for objects with radii 1 km ≤r≤ 10 km. Additionally, we found that the probability that these collisions remove enough orbital energy to yield a bound orbit was ≲10−5 and had very little dependence on the relative size of the planetesimals. Of these collisions, the collision energy between two objects was ≳103 times the gravitational binding energy for objects with radii ∼100 km. We find that capturing irregular satellites via collisions between unbound objects can only account for ∼0.1 per cent of the observed population, hence this cannot be the sole method of producing irregular satellites.

2008 LC18: a potentially unstable Neptune Trojan

“…Horner & Evans 2006), and have also been proposed as a potential capture mechanism for the irregular satellites of the giant planets during the early stages of Solar system evolution (e.g. Koch & Hansen 2011). However, we note that the longevity of the unstable clones as Neptune Trojans (time‐scales of tens of millions of years) is far longer than those recorded for the temporary Trojan captures around the other giant planets detailed in Horner & Evans (2006).…”

FOMALHAUT b AS A CLOUD OF DUST: TESTING ASPECTS OF PLANET FORMATION THEORY

“…Continuous capture models combine aspects of both approaches (e.g., Ruskol 1972;Weidenschilling 2002;Estrada & Mosqueira 2006;Koch & Hansen 2011). In this picture, a massive planet lies embedded within a circumstellar disk.…”

“…The evolution of solids within a captured cloud or disk depends on the accumulation rate. Here, we distinguish between the relatively rapid capture of a massive swarm of satellites during the early evolution of the planetary system (e.g., Nesvorný et al 2007) from the slow capture of material throughout the evolution of the planetary system (e.g., Ruskol 1972;Weidenschilling 2002;Estrada & Mosqueira 2006;Koch & Hansen 2011). Prompt captures over a few Myr enable the immediate onset of a collisional cascade and formation of a massive dust cloud.…”

“…Originally envisioned as an explanation for the origin of the Moon (Ruskol 1961), the capture of circumstellar material onto circumplanetary orbits provides an interesting alternative to dust formation from a giant impact (for an application to satellite formation around Jupiter, see Estrada & Mosqueira 2006;Koch & Hansen 2011). In the simplest form of this model, an object enters the Hill sphere of a planet and collides with another object passing through the Hill sphere (Ruskol 1972), a satellite of the planet (Durda & Stern 2000;Stern 2009), or the planet (Wyatt & Dent 2002;.…”

2004 KV18: a visitor from the scattered disc to the Neptune Trojan population

“…A common theme of those studies is that the Neptunian Trojans simply cannot have been formed in situ – instead, it is thought that the Neptunian Trojans were captured during the outward migration of the giant planet after its formation, a process also invoked to explain a number of features of the various other populations of Solar system objects (e.g. Malhotra ; Morbidelli et al ; Lykawka & Mukai , , ; Minton & Malhotra ; Koch & Hansen ).…”