The Short Rotation Period of Hi'iaka, Haumea's Largest Satellite

TL;DR

This paper reports the discovery of Hi'iaka's unusually rapid 9.8-hour rotation period, which challenges existing tidal evolution models and provides new insights into the formation and dynamical history of the Haumea system.

Contribution

The study presents the first measurement of Hi'iaka's rotation period and analyzes its implications for tidal evolution and formation scenarios of the Haumea system.

Findings

Hi'iaka's rotation period is approximately 9.8 hours.

Rapid rotation suggests significant obliquity and potential spin precession.

Despinning tides may not lead to synchronous rotation, even near the Roche limit.

Abstract

Hi'iaka is the larger outer satellite of the dwarf planet Haumea. Using relative photometry from the Hubble Space Telescope and Magellan and a phase dispersion minimization analysis, we have identified the rotation period of Hi'iaka to be ~9.8 hrs (double-peaked). This is ~120 times faster than its orbital period, creating new questions about the formation of this system and possible tidal evolution. The rapid rotation suggests that Hi'iaka could have a significant obliquity and spin precession that could be visible in light curves within a few years. We then turn to an investigation of what we learn about the (presently unclear) formation of the Haumea system and family based on this unexpectedly rapid rotation rate. We explore the importance of the initial semi-major axis and rotation period in tidal evolution theory and find they strongly influence the time required to despin to synchronous rotation, relevant to understanding a wide variety of satellite and binary systems. We find that despinning tides do not necessarily lead to synchronous spin periods for Hi'iaka, even if it formed near the Roche limit. Therefore the short rotation period of Hi'iaka does not rule out significant tidal evolution. Hi'iaka's spin period is also consistent with formation near its current location and spin up due to Haumea-centric impactors.