Retrograde orbits excess among observable interstellar objects

Abstract

In this work we investigate the orbital distribution of interstellar objects (ISOs), observable by the future wide-field National Science Foundation Vera C. Rubin Observatory (VRO). We generate synthetic population of ISOs and simulate their ephemerides over a period of 10 years, in order to select those which may be observed by the VRO, based on the nominal characteristics of this survey. We find that the population of the observable ISOs should be significantly biased in favor of retrograde objects. The intensity of this bias is correlated with the slope of the size-frequency distribution (SFD) of the population, as well as with the perihelion distances. Steeper SFD slopes lead to an increased fraction of the retrograde orbits, and also of the median orbital inclination. On the other hand, larger perihelion distances result in more symmetric distribution of orbital inclinations. We believe that this is a result of Holetschek’s effects, which is already suggested to cause observational bias in orbital distribution of long period comets. The most important implication of our findings is that an excess of retrograde orbits depends on the sizes and the perihelion distances. Therefore, the prograde/retrograde orbits ratio and the median inclination of the discovered population could, in turn, be used to estimate the SFD of the underlying true population of ISOs.

Synthetic Population of Interstellar Objects in the Solar System

“…Previous analyzes involving synthetic populations of ISOs (e.g. Engelhardt et al, 2017;Marčeta and Novaković, 2020) used a technique developed by Grav et al (2011). This technique is based on propagating an initially homogeneous and isotropic population over a sufficiently long time so that the resulting population represents a steady-state population altered by the effect of gravitational focusing in some predefined sphere surrounding the Sun.…”

“…thetic populations within such large heliocentric spheres. For example, Engelhardt et al (2017) and Marčeta and Novaković (2020) analysed synthetic populations inside model spheres with radii 50 au and 100 au, respectively. The reason for this was that objects within these spheres are capable of reaching heliocentric distances at which they could be detected by the LSST survey during the defined nominal duration of this survey of 10 years (LSST Science Collaboration et al, 2017).…”

“…Such a model can be very useful for developing algorithms for determining their orbits (e.g. Gronchi et al, 2021) and analysing their detection rates (Marčeta and Novaković, 2020;Hoover et al, 2022) by the future sky surveys. On the other hand, it is also related to the exploration of dynamical mechanisms for their permanent capture by the planetary systems and the Solar System in particular (Napier et al, 2021a,b).…”

Impact of non-gravitational effects on chaotic properties of retrograde orbits

“…The particular example shown in this work showed that the probability of such an event is significant. Moreover, the latest simulations of Marčeta & Novaković (2020) indicate that there are a very large number of retrograde orbits among interstellar objects. This is a serious clue to further exploration in this area.…”