High-drag Interstellar Objects and Galactic Dynamical Streams

Abstract

The nature of 1I/'Oumuamua (henceforth, 1I), the first interstellar object known to pass through the solar system, remains mysterious. Feng & Jones noted that the incoming 1I velocity vector "at infinity" (v ∞ ) is close to the motion of the Pleiades dynamical stream (or Local Association), and suggested that 1I is a young object ejected from a star in that stream. Micheli et al. subsequently detected non-gravitational acceleration in the 1I trajectory; this acceleration would not be unusual in an active comet, but 1I observations failed to reveal any signs of activity. Bialy & Loeb hypothesized that the anomalous 1I acceleration was instead due to radiation pressure, which would require an extremely low mass-to-area ratio (or area density). Here I show that a low area density can also explain the very close kinematic association of 1I and the Pleiades stream, as it renders 1I subject to drag capture by interstellar gas clouds. This supports the radiation pressure hypothesis and suggests that there is a significant population of low area density ISOs in the Galaxy, leading, through gas drag, to enhanced ISO concentrations in the galactic dynamical streams. Any interstellar object entrained in a dynamical stream will have a predictable incoming v ∞ ; targeted deep surveys using this information should be able to find dynamical stream objects months to as much as a year before their perihelion, providing the lead time needed for fast-response missions for the future in situ exploration of such objects.

Interstellar objects follow the collapse of molecular clouds

“…As MCs form and dissolve throughout the Milky Way, this could result in a rather inhomogeneous ISO concentration in the ISM, on timescales of several tens of Myr. This mechanism is independent of requiring substantial populations of low-area-density ISOs, in contrast to the process to concentrate ISOs in stellar streams proposed by Eubanks (2019). With inhomogeneity in play, the question arises of how typical the local ISO concentration that we measure with surveys in the Solar System is for the entire Galaxy (see also Pfalzner et al (2020)).…”

The NAROO digitization center

“…The scientific interest of these anterior discoveries are mainly to contribute to the statistics of ISOs and to assess their frequency in time. Indeed, galactic tides may change their apparition frequency in the Solar System (Eubanks 2019). For instance, Siraj & Loeb (2020) showed that they may present a directional asymmetry leading a better understanding of planetary system origin and nature.…”

Exobodies in Our Back Yard: Science from Missions to Nearby Interstellar Objects

“…The stream velocity estimates are from [Kushniruk et al, 2017], supplemented by [Chereul et al, 1998, Liang et al, 2017, Gaia Collaboration et al, 2018. The 1I and LSR velocites are as shown in [Eubanks, 2019b], and the 2I velocity estimate is from the ephemeris of Bill Grey / Project Pluto.…”

“…(1) indicating these objects may pass through the inner solar system more or less continuously and that targeted searches [Eubanks, 2019b] or more sensitive survey instruments such as the VRT [Trilling et al, 2017] may be able to find numerous targets for future missions.…”