An Etymological Dictionary of Astronomy and Astrophysics

The fourth largest → main belt asteroid and the only known → asteroid whose surface composition appears similar to that of the dwarf planet Ceres, suggesting a similar origin for these two objects. Hygiea suffered a giant impact more than 2 Gyr ago that is at the origin of one of the largest asteroid families. High angular resolution imaging observations of Hygiea with the VLT/SPHERE instrument (~20 mas at 600 nm) reveal a basin-free nearly spherical shape with semi-axes of 225 ± 5 km, 215 ± 5 km, and 212 ± 10 km and a volume equivalent radius of 217 ± 7 km.

The shape and the best estimate of Hygiea’s mass, (8.32 ± 0.80) × 10¹⁹ kg, yield a density of 1944 ± 250 kg m^-3.

Such density is compatible, within errors, with Ceres’ density (2161.6 ± 2.5 kg m^-3).

These observations moreover, yield a new rotation period of ~ 13.8h for Hygiea, that is half of the currently accepted value. Numerical simulations of the family forming event show that Hygiea’s spherical shape and family can be explained by a collision with a large projectile (Diameter ~ 75-150 km). By comparing Hygiea’s sphericity with that of other solar system objects, it appears that Hygiea is nearly as spherical as Ceres, opening a possibility for this object to be reclassified as a dwarf planet (Vernazza et al., 2019, Nature Astronomy, 28 October).

See also: in Greek mythology Hugieia / Hugeia was a daughter of the god of medicine, Asclepius, and Epione. She was the goddess, personification of health, cleanliness and sanitation. Her Roman name is Hygea/Hygia or Salus.