The interstellar object 'Oumuamua as a fractal dust aggregate

Abstract

The first known interstellar object 'Oumuamua exhibited a nongravitational acceleration that appeared inconsistent with cometary outgassing, leaving radiation pressure as the most likely force. Bar the alien lightsail hypothesis, an ultra-low density due to a fractal structure might also explain the acceleration of 'Oumuamua by radiation pressure (Moro-Martin 2019). In this paper we report a decrease in 'Oumuamua's rotation period based on ground-based observations, and show that this spin-down can be explained by the YORP effect if 'Oumuamua is indeed a fractal body with the ultra-low density of $10^{-2}$ kg m${}^{-3}$. We also investigate the mechanical consequences of 'Oumuamua as a fractal body subjected to rotational and tidal forces, and show that a fractal structure can survive these mechanical forces.

arXiv comment8 pages, 3 figures

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• The Nucleus of Interstellar Comet 2I/Borisov
• 1I/'Oumuamua as an N2 ice fragment of an exo-Pluto surface: I. size and compositional constraints
• Outburst and Splitting of Interstellar Comet 2I/Borisov
• Constraints on the Occurrence of 'Oumuamua-Like Objects
• Evolution of porous dust grains in protoplanetary discs -- I. Growing grains
• Numerical Simulations of Tidal Deformation and Resulting Light Curves of Small Bodies: Material Constraints of 99942 Apophis and 1I/`Oumuamua
• Project Lyra: A Mission to 1I/'Oumuamua without Solar Oberth Manoeuvre
• Observable tests for the light-sail scenario of interstellar objects
• Constraining the orientation of the spin axes of extrasolar minor bodies 1I/2017 U1 (`Oumuamua) and 2I/Borisov
• The New Astronomical Frontier of Interstellar Objects
• Fitting the Light Curve of 1I/`Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques
• Project Lyra: Catching 1I/'Oumuamua -- Using Laser Sailcraft in 2030
• Discerning between different 'Oumuamua models by optical and infrared observations
• Machine Learning Methods for Automated Interstellar Object Classification with LSST