1I/'Oumuamua: A sample of an exo-Pluto, and the nearest exoplanet

1I/'Oumuamua was the first confirmed interstellar object (ISO) [1,2] and an immediate mystery. It had no dust tail or observed emission from H₂O, CO, etc. (N₂ was be invisible) [1,3]. Its non-gravitational acceleration varied as 1/d², as comets do from sublimation of ices, but 10 times greater than typical [4]. From light curves, its shape was a disk with extreme axis ratios 6:6:1 [5]. We show [6] all these mysteries are resolved if 'Oumuamua was a ~45m × 44m × 7.5m fragment of N₂ ice as seen on Pluto. Such fragments were necessarily ejected during the Solar System's dynamical instability [7]. Pluto's surface ice would match all constraints on 'Oumuamua's composition. The albedo, etc., of N₂ ice exactly matches its observed non-gravitational acceleration. The predicted ~92% mass loss at perihelion exactly explains its extreme shape. Collisions among the thousands of "plutos" in the early Solar System [8] would have ejected ~0.001 M_E of fragments [9]. If most stellar systems were similar, and accounting for cosmic ray erosion, [9,10] predict an interstellar density of fragments n_ISO = 0.0005 AU^-3, 1/3 of observed being N₂ ice. This matches observations (n_ISO = 0.003 AU^-3, 90% C.I. 0.00015 AU^-3< n_ISO < 0.009 AU^-3 [1,10]). Specious claims about the mass budget of N₂ ice needed to match n_ISO [11] are thoroughly debunked [10]. We [6,9,10] suggest 'Oumuamua was ejected from an exo-Pluto in a young stellar system in the Perseus arm ~0.5 Gyr ago. Kuiper Belts with thousands of plutos, and dynamical instabilities, must be common features of exoplanetary system architecture. In October 2017, the surface material of an exoplanet was directly observed at 0.1 AU.

References: [1] Meech K.J., et al. (2017) Nat., 552, 378. [2] 'Oumuamua ISSI Team (2019) Nat. Astro., 3, 594. [3] Trilling D.E., et al. (2018) AJ, 156, 261. [4] Micheli M., et al. (2018) Nat., 559, 223. [5] Mashchenko S. (2019) MNRAS, 489, 3003. [6] Jackson, A.P. & Desch, S.J. (2021) JGR 126, e06706. [7] Tsiganis K., et al. (2005) Nat., 435, 459. [8] Nesvorný D. & Vokrouhlický D. (2016) Ap.J., 825, 94. [9] Desch, S.J. & Jackson, A.P. (2021) JGR 126, e06807. [10] Desch, S.J. & Jackson, A.P. (2022), subm. Astrobiology. [11] Siraj, A. & Loeb, A. (2022), New Astron. 92, 101730.