2023/04/02 by Darryl Z. Seligman, Seligman, Darryl Z., Amaya Moro‐Martín +1 · 2 citations
Earth and Planetary Sciences · Physics and Astronomy · #Astro and Planetary Science #Astronomical and nuclear sciences #Astrophysics of Galaxies (astro-ph.GA) #Atmospheric Ozone and Climate #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences
paper · pdf · doi:10.48550/arxiv.2304.00568
openalex publication_date 2023/04/02 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Since 2017, two macroscopic interstellar objects have been discovered in the inner Solar System, both of which are distinct in nature. The first interstellar object, 1I/`Oumuamua, passed within ∼63 lunar distances of the Earth, appeared asteroidal lacking detectable levels of gas or dust loss, yet exhibited a nongravitational acceleration. 1I/`Oumuamua's brief visit left open questions regarding its provenance which has given rise to many theoretical hypotheses, including an icy comet lacking a dust coma, an elongated fragment of a planet or planetesimal that was tidally disrupted, and an ultra-porous fractal aggregate. The second interstellar object, 2I/Borisov, was distinct from 1I/`Oumuamua in terms of its bulk physical properties and displayed a definitive cometary tail. We review the discoveries of these objects, the subsequent observations and characterizations, and the theoretical hypotheses regarding their origins. We describe 1I/`Oumuamua and 2I/Borisov in the context of active asteroids and comets in the Solar System. The discovery of these two objects implies a galactic-wide population of ∼1026 similar bodies. Forthcoming observatories should detect many more interstellar planetesimals which may offer new insights into how planetary formation processes vary throughout the Galaxy.