Spinup and Disruption of Interstellar Asteroids by Mechanical Torques, and Implications for 1I/2017 U1 (`Oumuamua)

TL;DR

This paper investigates how mechanical torques from interstellar gas can spin up and disrupt interstellar asteroids, explaining `Oumuamua's shape and tumbling, and discussing their survival in galactic environments.

Contribution

It introduces a model for rotational dynamics of irregular interstellar asteroids under gas bombardment, linking mechanical torques to asteroid disruption and shape evolution.

Findings

Mechanical torques can spin up and break apart ISAs.

`Oumuamua's shape may result from binary reassembly after disruption.

Tumbling could be caused by rotational breakup due to mechanical torques.

Abstract

The discovery of the first interstellar asteroid, 1I/2017 U1 (`Oumuamua), has opened a new era for research on interstellar objects. In this paper, we study the rotational dynamics of interstellar asteroids (ISAs) of irregular shapes moving through the interstellar gas. We find that regular mechanical torques resulting from the bombardment of gas flow on the irregular body could be important for the dynamics and destruction of ISAs. Mechanical torques can spin up the ISA, resulting in the breakup of the original ISA into small binary asteroids when the rotation rate exceeds the critical frequency. We find that the breakup timescale is short for ISAs of highly irregular shapes and low tensile strength. We apply our results to the first observed ISA, `Oumuamua, and suggest that its extreme elongated shape may originate from a reassembly of the binary fragments due to gravity along its journey in the interstellar medium. The tumbling of `Oumuamua could have been induced by rotational disruption due to mechanical torques. Finally, we discuss the survival possibility of high-velocity asteroids presumably formed by tidal disruption of planetary systems by the black hole at the Galactic center.