Finding the imprints of stellar encounters in long-period comets

Abstract

The solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the solar system, where they may be observed as the long-period comets (periods longer than 200 years). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5% of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong -but as yet unidentified -stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8% and 6% to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.

The unseen planets of double belt debris disc systems

“…There is some theoretical basis to believe planet formation may be ∼ 50% efficient (Goldreich, Lithwick & Sari 2004a,b). There is some circumstantial observational evidence of this; the estimated mass of the Oort cloud (Francis 2005;Feng & Bailer-Jones 2015) and calculated fraction of small bodies that end up in the Oort cloud (e.g. Brasser & Morbidelli 2013; imply the mass of solids scattered by the planets was comparable to the mass of solids in the planets.…”

The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release

“…For the much rarer, very close approaches (on the order of the comet-Sun separation), the dependence on distance is more like 1/d ph (see Feng & Bailer-Jones 2015, for some empirical comparison). More sophisticated modelling of the effect of passing stars on the Oort cloud has been carried out by, for example, Scholl et al (1982), Weissman (1996), Dybczyński (2002), Fouchard et al (2011), Rickman et al (2012).…”

“…More sophisticated modelling of the effect of passing stars on the Oort cloud has been carried out by, for example, Scholl et al (1982), Weissman (1996), Dybczyński (2002), Fouchard et al (2011), Rickman et al (2012). Feng & Bailer-Jones (2015) looked specifically at the consequence of the closest encounters found in Paper I. Our ability to find and characterize close encounters has received a huge boost by the launch of the Gaia astrometric satellite in December 2013 (Gaia Collaboration 2016b).…”

Finding Planet Nine: apsidal anti-alignment Monte Carlo results

“…A number of plausible explanations have been suggested. These include the possible existence of one (Trujillo & Sheppard 2014;Gomes et al 2015;Malhotra et al 2016) or more (de la Fuente Marcos & de la Fuente Marcos 2014, 2016bde la Fuente Marcos et al 2015, 2016 trans-Plutonian planets, capture of ETNOs within the Sun's natal open cluster (Jílková et al 2015), stellar encounters (Brasser & Schwamb 2015;Feng & Bailer-Jones 2015), being a by-product of Neptune's migration (Brown & Firth 2016) or the result of the inclination instability (Madigan & McCourt 2016), and having been induced by Milgromian dynamics (Paučo & Klačka 2016).…”