Could Solar Radiation Pressure Explain ‘Oumuamua’s Peculiar Acceleration?

Abstract

Oumuamua (1I/2017 U1) is the first object of interstellar origin observed in the Solar System. Recently, Micheli et al. (2018) reported that 'Oumuamua showed deviations from a Keplerian orbit at a high statistical significance. The observed trajectory is best explained by an excess radial acceleration ∆a ∝ r −2 , where r is the distance of 'Oumuamua from the Sun. Such an acceleration is naturally expected for comets, driven by the evaporating material. However, recent observational and theoretical studies imply that 'Oumuamua is not an active comet. We explore the possibility that the excess acceleration results from Solar radiation pressure. The required mass-to-area ratio is (m/A) ≈ 0.1 g cm −2 . For a thin sheet this requires a thickness of ≈ 0.3 − 0.9 mm. We find that although extremely thin, such an object would survive an interstellar travel over Galactic distances of ∼ 5 kpc, withstanding collisions with gas and dust-grains as well as stresses from rotation and tidal forces. We discuss the possible origins of such an object. Our general results apply to any light probes designed for interstellar travel. Subject headings: ISM: individual objects (1I/2017 U1) -minor planets, asteroids: individual (1I/2017 U1) -General: extraterrestrial intelligence -Minor planets, asteroids: general

Modelling the light curve of ‘Oumuamua: evidence for torque and disc-like shape

“…As this is a self-consistent brightness ellipsoid model, the degeneracy is present for both kinematic and brightness ellipsoids. As a result, our SAIL model is consistent with the extremely low surface density requirement of the solar sail hypothesis of Bialy & Loeb (2018).…”

“…The first auxiliary model is identical to our fiducial model (LS ellipsoid brightness model + constant torque; subsection 4.3) in all aspects except for numerical values of some parameters -the thickness (parameter c), which now has the initial range (soft limits) between 10 −4 and 10 −2 (the range was [0.01, 1] in the fiducial model), and the length of the intermediate semi-axis b (new soft limits: [0.3, 1]). These numerical runs were an attempt to use our model's framework to explore the idea of Bialy & Loeb (2018) that 'Oumuamua is a solar sail -an extremely thin object, with very low surface density (∼ 0.1 g cm −2 ).…”

“…Let us assume 'Oumuamua is a flat disc-shaped sail of radius R with one of the sides consisting of a darker (albedo p 1 ) and brighter (albedo p 2 ) halves. Radiation pressure can be computed as P = (1 + p)C, where p is the albedo and C is a constant when the distance from the Sun is fixed (Bialy & Loeb 2018). An element with the surface area dS will experience force d f = P dS.…”

Project Lyra: Catching 1I/‘Oumuamua – Mission opportunities after 2024

“…Since its discovery in October 2017, 1I/'Oumuamua has generated considerable interest from both academia and the media. The academic debate is still ongoing and topics are as wide-ranging as the object's shape [4][5][6][7][8][9], its composition [4,5,[10][11][12][13][14], its origin [15][16][17][18][19][20][21], explanation for an observed acceleration [22,23], and estimates for the population of similar objects [2,5]. Given that 1I/'Oumuamua is the first confirmed interstellar object that has been discovered intercepting our Solar System, it might turn out to be the only opportunity to study interstellar material in-situ for decades or even centuries to come [2,5].…”

Effect of interstellar objects on metallicity of low-mass first stars formed in a cosmological model

“…The high number density can be explained by the amount of debris ejected during the formation process of planets (Portegies Zwart et al 2018). However, the situation that non-gravitational acceleration was observed despite no sign of a cometary tail (Meech et al 2017;Fitzsimmons et al 2018) is still puzzling (Bialy & Loeb 2018).…”