The Short Rotation Period of Hi'iaka, Haumea's Largest Satellite
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 hr (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 (currently unclear) formation of the Haumea system and family based on this unexpectedly rapid rotation rate. We explore the importance of the initial semimajor axis and rotation period in tidal evolution theory and find that 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.
Additional Information© 2016 The American Astronomical Society. Received 2016 August 12; revised 2016 September 28; accepted 2016 September 29; published 2016 November 29. We thank Marc Buie for sharing his IDL library, including the PDM2 code that was used in this work. D.R. acknowledges discussions with Matija Ćuk and others concerning possible explanations for Hi'iaka's unexpectedly rapid spin rate. We wish to thank the anonymous reviewers for their comments and suggestions, which improved the quality of this paper. Support was provided by NASA through grant HST-GO-13873 from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Published - Hastings_2016_AJ_152_195.pdf
Submitted - 1610.04305v1.pdf