(10) Hygiene

(10) Hygiea or Higía is an asteroid belonging to the asteroid belt that orbits between the planets Mars and Jupiter, discovered on April 12, 1849 by the Italian astronomer Annibale de Gasparis (1819-1892) from the Capodimonte observatory in Naples, Italy. It is named after Hygieia, a goddess from Greek mythology. The name was suggested by Ernesto Capocci (1798-1864). Although they added the adjective "Borbonica" to the name, in honor of the royal house of Naples, it soon fell into disuse.

It is the fourth largest, with a mean diameter of 400 km, and an estimated mass of 3% of the total asteroid belt. However, it was the tenth to be identified because its dark surface makes the asteroid less visible than it would be for its size. In fact, it reaches on average magnitude 10.2 in opposition.

Orbital characteristics

Hygiea is located at an average distance from the Sun of 3,139 AU, being able to move away up to 3,501 AU and approach up to 2,778 AU. It has an eccentricity of 0.1153 and an orbital inclination of 3.841°. It takes 2032 days to complete an orbit around the Sun. It gives its name to the asteroidal family of Hygieia.

Physical characteristics

Based on spectral evidence, the surface of Hygiea is thought to consist of primitive carbonaceous materials similar to those found in meteoritic carbonaceous chondrites. Residues of aqueous alteration have been detected on the surface, which could indicate the presence in the past of water ice that got hot enough to melt. The presence of such a primitive surface composition would indicate that (10) Hygiea did not melt. would have differentiated during the formation of the solar system  in contrast to other large planetesimals such as Vesta.

Hygieia is the main member of the Hygieia family (contains more than 90% of the mass) and the largest of the dark C-type asteroids dominant in the outer asteroid belt, which extends beyond 2, 82 au. Due to its shape, it is a spheroid visibly flattened at the poles, with a mean diameter of 444 ± 35 km and a semi-axis ratio of 1.11—the largest among the four largest objects in the belt. Like Ceres, its density it is relatively low, more similar to that of the moons of Jupiter and Saturn than to rocky planets and asteroids.

Due to its dark surface and great distance from the Sun, it appears very faint when viewed from Earth despite being the largest body in its region. In fact, it is the third faintest of the first twenty-three asteroids discovered: only Egeria and Tethys have lower brightnesses at opposition. At most oppositions, Hygieia has a magnitude of 10.2—four orders lower than Vesta's. —, so a telescope of at least four inches is needed to see it. However, in a perihelion opposition it can be seen with 10×50 binoculars, since it can reach a magnitude of 9.1. In contrast, the next two largest asteroids, Interamnia and Davida, are always beyond the visibility of binoculars or binoculars.

At least five stellar occultations of Hygieia have been tracked from Earth, but with so few independent observers that its shape has not been deduced. The Hubble Space Telescope has resolved the asteroid and ruled out the presence of an orbital companion larger than 16 km in diameter.

Rotation

Its rotation is unusually slow. It takes 27 hours and 37 minutes to rotate on its axis, while most large asteroids have rotations of between 6 and 12 hours. Its direction of spin is thought to be retrograde, although there is ambiguity in the light curve data exacerbated by its long rotation period which makes telescopic viewing periods only a fraction of the rotation at best. light curve analysis indicates that the poles of Hygieia point towards the ecliptic coordinates (β, λ) = (30°, 115°) or (30°, 300°) with 10° uncertainty. This gives an axial inclination of approximately 60° in both cases.