Constraints on the Occurrence of 'Oumuamua-Like Objects

Abstract

At present, there exists no consensus in the astronomical community regarding either the bulk composition or the formation mechanism for the interstellar object 1I/2017 U1 ('Oumuamua). With the goal of assessing the merits of the various scenarios that have been suggested to explain 'Oumuamua's appearance and observed properties, we report a number of new analyses and provide an up-to-date review of the current hypotheses. We consider the interpretations that can reconcile 'Oumuamua's observed non-Keplerian trajectory with the non-detection of traditional cometary volatiles. We examine the ability of these proposed formation pathways to populate the galaxy with sufficient interstellar objects such that the detection of 'Oumuamua by Pan-STARRS would be statistically-favored. We consider two exotic ices, hydrogen and nitrogen, showing that the frigid temperature requirement for the former and the necessary formation efficiency of the latter pose serious difficulties for these interpretations. Via order-of-magnitude arguments and hydrodynamical cratering simulations, we show that impacts on extrasolar Kuiper Belt analogues are not expected to generate N 2 ice fragments as large as 'Oumuamua. In addition, we discuss observational tests to confirm the presence of these ices in future interstellar objects. Next, we examine the explanations that attribute 'Oumuamua's properties to other compositions: ultra-porous dust aggregates and thin membranes powered by solar radiation pressure, among others. While none of these hypotheses are perfectly satisfactory, we make predictions that will be testable by the Vera Rubin Observatory to resolve the tension introduced by 'Oumuamua.

Interstellar planetesimals

“…Yet, only two objects have been identified so far and they are remarkably different, the unusual properties of 1I/'Oumuamua contrasting sharply with the unquestionably extrasolar cometary nature of 2I/Borisov. Starting in 2023, the Vera Rubin Observatory will systematically survey the sky more deeply than has ever been attempted and it will do it repeatedly, revolutionizing this field with the detection of dozens to a hundred of new interstellar objects (Levine et al 2021), in addition to a tenfold increase in the number of solar system object detections (Ivezić et al 2019). These observations will constrain the number density, size, and velocity distributions of interstellar objects and will allow their early monitoring with follow-up observations, including with JWST, allowing to study their nature and origin.…”

Predicting the water content of interstellar objects from galactic star formation histories

“…Each stellar system contributes to a progressively accumulated background population of ISOs that builds up through Galactic history (Moro-Martín et al 2009;Moro-Martín 2018;Pfalzner & Bannister 2019), and which is then sampled as the Solar System moves through the Milky Way. While more exotic processes may also contribute to the ISO population (see Levine et al (2021) for an overview of current hypotheses), we address only planetesimal contributions in this initial study.…”