Perihelion evolution of observed new comets implies the dominance of the galactic tide in making Oort cloud comets discernable

Abstract

For an Oort cloud comet to be seen as a new comet, its perihelion must be moved from a point exterior to the loss cylinder boundary to a point interior to observable limits in a single orbit. The galactic tide can do this continuously, in a non-impulsive manner.Near-parabolic comets, with specific angular momentum H ∝ √ q, will most easily be made observable. Therefore, to reduce the perihelion distance, H must decrease. Since weakly perturbed comets are, in general, more numerous than strongly perturbed comets, we can anticipate that new comets made observable by a weak tidal torque will more likely be first observed when their slowly changing perihelion distances are approaching their minimum osculating values under the action of the tide, rather than receding from their minimum values.That is, defining ∆H tide as the vector change due to the galactic tidal torque during the prior orbit, and H obs as the observed vector, the sign S ≡ Sign(H obs · ∆H tide ) will more likely be −1 than +1 if a weak galactic tidal perturbation indeed dominates in making comets observable.Using comet data of the highest quality class (1A) for new comets (a > 10,000 AU), we find that 49 comets have S = −1 and 22 have S = +1. The binomial probability that as many or more would exhibit this characteristic if in fact S = ∓1 were equally likely is only 0.0009.This characteristic also persists in other long-period comet populations, lending support to the notion that they are dominated by comets recently arrived from the outer Oort Cloud. The preponderance of S = −1 also correlates with weakly perturbed (i.e., smaller semimajor axis) new comets in a statistically significant manner. This is strong evidence that the data are of sufficiently high quality and sufficiently free of observational selection effects to detect this unique imprint of the tide.

Long-term effects of the Galactic tide on cometary dynamics

“…Thus, the values of the local density ρ of the Galactic disk used in the Oort cloud literature span from 0.08 (Matese and Lissauer, 2004) to 0.18 M pc −3 (Matese and Whitman 1992), with two values being used more often: 0.1 M pc −3 (Levison et al 2001;Fouchard 2004;Fouchard et al 2005) and 0.15 M pc −3 (Wiegert and Tremaine 1999;Neslušan and Jakubík 2005).…”

“…Many studies have been devoted to the qualitative characteristics of the Galactic tide (Heisler and Tremaine 1986;Whitman 1989, 1992;Breiter et al 1996;Brasser 2001;Breiter and Ratajczak 2005), while quantitative studies have been performed mostly through integrations over short-time spans (most recently, Lissauer 2004 andDybczyński 2005). Long-term simulations of Oort cloud dynamics have either treated a small number of comets or made use of simplifications in the dynamical models (Wiegert and Tremaine 1999;Levison et al 2001;Neslušan and Jakubík 2005).…”

Galactic planar tides on the comets of Oort Cloud and analogs in different reference systems. I.

“…The inner Oort cloud comets have aphelion Q < 20 000 AU, while the outer ones have Q > 20 000 AU. At large distances from the Sun, the Galactic tidal force (Masi et al 2009;Matese & Lissauer 2004;Heisler & Tremaine 1986) is one of the dominant perturbers of comet orbits with stellar perturbations (Hills 1981;Matese & Lissauer 2002) and giant molecular clouds (GMCs; Bailey 1983). We will focus our attention to the first one neglecting, in this context, the other two.…”

Where do long-period comets come from? Moving through the Jupiter-Saturn barrier

“…Analysing the Galactic evolution of cometary perihelion distances, Matese & Lissauer (2004) introduced the so‐called tidal characteristic ‘ S ’, which describes whether the perihelion distance of a particular comet decreases ( S =−1) or increases ( S =+1) during the observed perihelion passage. In a dynamical model restricted to the Galactic‐disc tide, S =−sign[sin(2ω)].…”