Hygiea

Hygiea is the fourth-largest object in the asteroid belt with a diameter of 433 km, orbiting at 3.14 AU. It is the largest member of the carbonaceous C-type asteroids and the parent body of the Hygiea asteroid family — the most populous family in the outer main belt. Hygiea's surface is very dark (albedo 0.063) and composed of hydrated and ammoniated silicate minerals, carbonates, and water ice, making it one of the most primitive bodies in the solar system. Recent observations with the VLT's SPHERE instrument revealed that Hygiea is surprisingly spherical for its size, leading to discussions about whether it should be reclassified as a dwarf planet — which would make it the smallest in the solar system.

Hygiea is a faint target at magnitude 9.0 at best, requiring at least a 3-inch (75 mm) telescope to spot. It appears as a dim star-like point and is best identified by its motion over consecutive nights using a detailed finder chart. Because of its distance from the Sun (3.14 AU), Hygiea moves more slowly against the background stars than inner belt asteroids — patience is needed when tracking it. Oppositions occur roughly every 15 months. A computerized go-to mount is very helpful for locating this dim object, as it can easily be lost among similarly faint background stars.

Hygiea was discovered on April 12, 1849 by Italian astronomer Annibale de Gasparis at the Observatory of Capodimonte in Naples. It was named after Hygieia, the Greek goddess of health and hygiene — a fitting choice, as the modern words 'hygiene' and 'hygienic' derive from her name. Hygiea has never been visited by a spacecraft. In 2019, high-resolution images from the European Southern Observatory's Very Large Telescope revealed its nearly spherical shape, reigniting the debate about its potential dwarf planet status under the IAU definition.