[12] Although it is the largest body in its region, due to its dark surface and farther-than-average distance from the Sun, Hygiea appears very dim when observed from Earth.

[17] The Hubble Space Telescope has resolved the asteroid and ruled out the presence of any orbiting companions larger than about 16 kilometres (9.9 mi) in diameter.

He chose to call it Igea Borbonica ("Bourbon Hygieia"), after the Greek goddess of health, daughter of Asclepius, and in honor of the ruling family of the Kingdom of the Two Sicilies where Naples was located.

Observations taken with the Very Large Telescope's SPHERE imager in 2017 and 2018 revealed that Hygiea is nearly spherical and is close to a hydrostatic equilibrium shape and thus is a possible dwarf planet.

Aqueous alteration products have been detected on its surface, which could indicate the presence of water ice in the past which was heated sufficiently to melt.

[21] The primitive present surface composition indicates that Hygiea had not melted during the early period of Solar System formation.

[6] No deep basins are visible in VLT images, indicating that any large craters that formed after re-accretion must have flat floors, consistent with an icy C-type composition.

[7] In images taken with the VLT in 2017, a bright surface feature is visible, as well as at least two dark craters, which have been informally[b] named Serpens and Calix after the Latin words for 'snake' and 'cup', respectively.

[6] Aside from being the smallest of the "big four", Hygiea has a relatively low density of 2.06±0.20,[6] comparable to Ceres (2.16) and the larger icy satellites of the Solar System (Ganymede 1.94, Callisto 1.83, Titan 1.88, Triton 2.06) rather than to Pallas (2.9±0.1) or Vesta (3.45).

[27][failed verification] At aphelion Hygiea reaches out to the extreme edge of the asteroid belt at the perihelia of the Hilda family, which is in a 3:2 orbital resonance with Jupiter.

[citation needed] The family was formed when an object with a diameter of about 100 km collided with proto-Hygiea about 2 billion years ago.