Oort cloud and Scattered Disc formation during a late dynamical instability in the Solar System

Abstract

One of the outstanding problems of the dynamical evolution of the outer solar system concerns the observed population ratio between the Oort Cloud (OC) and the Scattered Disc (SD): observations suggest that this ratio lies between 100 and 1 000 but simulations that produce these two reservoirs simultaneously consistently yield a value of the order of 10. Here we stress that the populations in the OC and SD are inferred from the observed fluxes of new Long Period Comets (LPCs) and Jupiter-family comets (JFCs), brighter than some reference total magnitude. However, the population ratio estimated in the simulations of formation of the SD and OC refers to objects bigger than a given size. There are multiple indications that LPCs are intrinsically brighter than JFCs, i.e. an LPC is smaller than a JFC with the same total absolute magnitude. When taking this into account we revise the SD/JFC population ratio from our simulations relative to Duncan and Levison (1997), and then deduce from the observations that the size-limited population ratio between the OC and the SD is 44 +54 −34 . This is roughly a factor of four higher than the value 12 ± 1 that we obtain in simulations where the OC and the SD form simultaneously while the planets evolve according to the so-called 'Nice model'. Thus, we still have a discrepancy between model and 'observations, but the agreement cannot be rejected by the null hypothesis.

An updated estimate of the number of Jupiter-family comets using a simple fading law

“…Their work was followed by who concluded that the scattered disc and not the Kuiper belt had to produce the JFCs, a conclusion that was confirmed in subsequent works by Emel'yanenko et al (2004), Volk & Malhotra (2008), and Brasser & Morbidelli (2013). also reported that the scattered disc had to contain 6×10 8 objects with diameter D > 2 km, confirmed by Volk & Malhotra (2008).…”

“…Since the JFCs originate in scattered disc Emel'yanenko et al 2004;Volk & Malhotra 2008;Di Sisto et al 2009;Brasser & Morbidelli 2013), we also update the inferred number of scattered disc objects (SDOs) by using the total number of active JFCs as a proxy. To compare our simulation with the observational data we need to have an observational catalogue of comets that is as complete as possible.…”

“…The third is the source of the so-called Jupiter-family comets (JFCs), a population of comets whose orbits stay close to the ecliptic Volk & Malhotra 2008;Brasser & Morbidelli 2013). In this study we adhere to the definition of Levison (1996) which states that a JFC has T J ∈ (2, 3) and a < 7.35 AU (period P < 20 yr).…”

“…Here Article published by EDP Sciences A102, page 1 of 7 we apply the same fading law and techniques to numerical simulations of JFC production, and determine whether this reproduces their orbital distribution and the increase in total absolute magnitude determined from observations. We use the results of the fading law to update the number of JFCs with a diameter larger than 2.3 km estimated in Brasser & Morbidelli (2013). This paper is organised as follows.…”

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

“…Based on this model, the D/H determined in all OCCs would be expected to show greater scatter from the average value of ∼ 3.00 × 10 −4 . Brasser and Morbidelli (2013) suggest, however, that JFCs and OCCs originated from the same extended outer region of the PSN. This would mean that comets like Hartley 2, which has a lower D/H, formed closer to the Sun and comets with a higher D/H, like 67P/Churyumov-Gerasimenko (hereafter 67P/CG) formed farther out (Altwegg et al 2015).…”