Orbit and rotation::10 Hygiea


Hygiea::title    Author::journal    Asteroid::category    Jpldata::surface    Which::ceres    First::barucci

Orbit and rotation

A rotating frame depiction of asteroid Hygeia's orbital motion relative to Jupiter; the latter (purple loop at upper right) is held nearly stationary.
Animated orbit of Hygiea relative to the orbits of the terrestrial planets and Jupiter.

Generally, Hygiea's properties are the most poorly known out of the "big four" objects in the asteroid belt. Its orbit is much closer to the plane of the ecliptic than those of Ceres, Pallas or Interamnia,<ref name=Barucci/> but is less circular than Ceres or Vesta with an eccentricity of around 12%.<ref name=jpldata /> Its perihelion is at a quite similar longitude to those of Vesta and Ceres, though its ascending and descending nodes are opposite to the corresponding ones for those objects. Although its perihelion is extremely close to the mean distance of Ceres and Pallas, a collision between Hygiea and its larger companions is impossible because at that distance they are always on opposite sides of the ecliptic. In 2056, Hygiea will pass 0.025AU from Ceres, and then in 2063, Hygiea will pass 0.020AU from Pallas.<ref name=jpl-close>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> At aphelion Hygiea reaches out to the extreme edge of the asteroid belt at the perihelia of the Hilda family which is in 3:2 resonance with Jupiter.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Hygiea is used by the Minor Planet Center to calculate perturbations.<ref name="Perturbing"/>

It is an unusually slow rotator, taking 27 hours and 37 minutes for a revolution,<ref name=jpldata/> whereas 6 to 12 hours are more typical for large asteroids. Its direction of rotation is not certain at present, due to a twofold ambiguity in lightcurve data that is exacerbated by its long rotation period—which makes single-night telescope observations span at best only a fraction of a full rotation—but it is believed to be retrograde.<ref name=Barucci/> Lightcurve analysis indicates that Hygiea's pole points towards either ecliptic coordinates (β, λ) = (30°, 115°) or (30°, 300°) with a 10° uncertainty.<ref name="Kaasalainen2002">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> This gives an axial tilt of about 60° in both cases.

10 Hygiea sections
Intro  Discovery and name  Physical characteristics  Orbit and rotation  See also   References    External links   

Orbit and rotation
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