On the rotation period and shape of the hyperbolic asteroid 1I/`Oumuamua (2017) U1 from its lightcurve

TL;DR

This study observed 'Oumuamua's lightcurve, constraining its rotation period to at least 5 hours and suggesting an elongated shape with an axial ratio of at least 3:1, with no evidence of a coma or tail.

Contribution

First detailed lightcurve analysis of 'Oumuamua providing constraints on its rotation period and shape from observational data.

Findings

Rotation period is at least 5 hours.

Axial ratio is at least 3:1.

No detectable coma or tail.

Abstract

We observed the newly discovered hyperbolic minor planet 1I/`Oumuamua (2017 U1) on 2017 October 30 with Lowell Observatory's 4.3-m Discovery Channel Telescope. From these observations, we derived a partial lightcurve with peak-to-trough amplitude of at least 1.2 mag. This lightcurve segment rules out rotation periods less than 3 hr and suggests that the period is at least 5 hr. On the assumption that the variability is due to a changing cross section, the axial ratio is at least 3:1. We saw no evidence for a coma or tail in either individual images or in a stacked image having an equivalent exposure time of 9000 s.