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Published June 2009 | Accepted Version + Published
Journal Article Open

Orbits and Masses of the Satellites of the Dwarf Planet Haumea (2003 EL61)


Using precise relative astrometry from the Hubble Space Telescope and the W. M. Keck Telescope, we have determined the orbits and masses of the two dynamically interacting satellites of the dwarf planet (136108) Haumea, formerly 2003 EL61. The orbital parameters of Hi'iaka, the outer, brighter satellite, match well the previously derived orbit. On timescales longer than a few weeks, no Keplerian orbit is sufficient to describe the motion of the inner, fainter satellite Namaka. Using a fully interacting three-point-mass model, we have recovered the orbital parameters of both orbits and the mass of Haumea and Hi'iaka; Namaka's mass is marginally detected. The data are not sufficient to uniquely determine the gravitational quadrupole of the nonspherical primary (described by J_2). The nearly coplanar nature of the satellites, as well as an inferred density similar to water ice, strengthen the hypothesis that Haumea experienced a giant collision billions of years ago. The excited eccentricities and mutual inclination point to an intriguing tidal history of significant semimajor axis evolution through satellite mean-motion resonances. The orbital solution indicates that Namaka and Haumea are currently undergoing mutual events and that the mutual event season will last for next several years.

Additional Information

© 2009 The American Astronomical Society. Received 2009 February 13; accepted 2009 March 24; published 2009 April 27. We thank Meg Schwamb, Aaron Wolf, Matt Holman, and others for valuable discussions and Eugene Fahnestock for kindly providing his code for gravity around tri-axial bodies. We also acknowledge observational support from Emily Schaller and Chad Trujillo. We especially acknowledge the encouragement and discussions of Dan Fabrycky. D.R. is grateful for the support of the Moore Foundation. This work was also supported by NASA Headquarters under the Earth and Space Sciences Fellowship and the Planetary Astronomy programs. This work is based on NASA/ESA Hubble Space Telescope program 11518 using additional data from programs 10545, 10860, and 11169. Support for all these programs was provided by NASA through grants HST-GO-10545, HST-GO-10860, HST-G0-11518, and HST-GO-11169 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. Some data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations of Haumea, Hi'iaka, and Namaka, which were named after Hawaiian goddesses.

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Published - Ragozzine2009p4463Astron_J.pdf

Accepted Version - 0903.4213.pdf


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