The origin of interstellar asteroidal objects like 1I/2017 U1 'Oumuamua (1711.03558v3)

Abstract: We study the origin of the interstellar object 1I/2017 U1 'Oumuamua by juxtaposing estimates based on the observations with simulations. We speculate that objects like 'Oumuamua are formed in the debris disc as left over from the star and planet formation process, and subsequently liberated. The liberation process is mediated either by interaction with other stars in the parental star-cluster, by resonant interactions within the planetesimal disc or by the relatively sudden mass loss when the host star becomes a compact object. Integrating backward in time in the Galactic potential together with stars from the Gaia-TGAS catalogue we find that about 1.3Myr ago 'Oumuamua passed the nearby star HIP 17288 within a mean distance of $1.3$pc. By comparing nearby observed L-dwarfs with simulations of the Galaxy we conclude that the kinematics of 'Oumuamua is consistent with relatively young objects of $1.1$--$1.7$Gyr. We just met 'Oumuamua by chance, and with a derived mean Galactic density of $\sim 3\times 10^{5}$ similarly sized objects within 100\,au from the Sun or $\sim 10^{14}$ per cubic parsec we expect about 2 to 12 such visitors per year within 1au from the Sun.

• The paper analyzes the origin of interstellar object 'Oumuamua using Galactic simulations and observational data, suggesting it likely originated from debris ejected during star and planet formation processes.
• The research estimates a substantial population of similar interstellar bodies exists in the galaxy, with potentially 2 to 12 objects per year entering within 1 au of the Sun.
• Understanding 'Oumuamua as a representative sample indicates a significant, previously underestimated component of the Galactic ecosystem, with future observations expected to reveal more such objects.

Insights into the Origin of Interstellar Object 1I/2017 U1 'Oumuamua

The paper under consideration, "The origin of interstellar asteroidal objects like 1I/2017 U1 'Oumuamua" by S. Portegies Zwart and collaborators, delivers a comprehensive analysis of the enigmatic interstellar object 'Oumuamua, examining its possible origins and implications for the presence of similar celestial bodies within our galaxy.

Origin and Characteristics of 'Oumuamua

'Oumuamua was distinguished by its hyperbolic orbit, implying an origin from outside our Solar System. Its discovery in 2017 prompted immediate reclassification from a comet to an unusual minor planet due to the absence of a visible cometary tail. The object exhibited a notable elongated shape and a rapid rotation period of roughly 8.1 hours, indicating it had experienced significant physical evolution possibly due to prolonged exposure to space environments.

This paper utilises observational data and Galactic simulations to hypothesize that 'Oumuamua-like objects might be debris liberated from the circumstellar disc formation processes, due to gravitational interactions within star clusters, or through star mass loss transitions. The possibility that 'Oumuamua might have travelled past the star HIP 17288 approximately 1.3 million years ago, within a distance of 1.3 parsecs, was a significant finding derived from backwards orbital integration against the Galactic potential and stellar data from the Gaia-TGAS catalogue.

Population Estimates and Detection

The estimated Galactic density of such interstellar bodies, derived in this paper, suggests a significant population with approximately $3 \times 10^5$ similar-sized objects expected within 100 astronomical units (au) from the Sun. This translates into the potential encounter of 2 to 12 similar objects per year entering within 1 au of the Sun. These figures are based on the derived volumes from the Pan-STARRS telescope observations with a magnitude limit of $m \sim 22$, and underline the significance of telescopic surveys for identifying such transient objects.

Implications and Theoretical Considerations

The hypothesis posited by the authors suggests that a significant population of these interstellar objects likely originate from the debris fields left over from the star and planet formation processes. This is inconsistent with the densities expected from ejected exo-Oort cloud or asteroid-like bodies, emphasizing the paper's stance on 'Oumuamua's probable disc ejecta origin.

The interstellar velocity trend measured aligns with characteristics expected from relatively young galactic entities (estimated at 1.1--1.7 Gyr), suggesting a commonality with the kinematic characteristics of L-dwarfs. The understanding of 'Oumuamua as a representative sample of a substantial population of similar bodies underscores the existence of a previously underestimated component of the Galactic ecosystem.

Conclusion and Future Outlook

The paper presents a compelling analysis of 'Oumuamua's origin, framed within the broader context of interstellar debris dynamics in the galaxy. It suggests a substantial population of similar bodies possibly originating during earlier phases of star formation. The upcoming advancements in observational technology, such as the Large Synoptic Survey Telescope (LSST), are anticipated to enhance the detection rate of these objects, allowing further investigation into their origins, composition, and implications for understanding planetary system evolution across the galaxy. The research thus not only sheds light on 'Oumuamua itself but also sets the stage for future explorations into the nature and movement of interstellar objects.