5th Largest Asteroid, 704 Interamnia

Interamnia is probably the fifth-most-massive asteroid after Ceres, Vesta, Pallas, and Hygiea. Interamnia is easily the largest of the F-type asteroids.

Discovery

Interamnia was discovered on October 2, 1910 by Vincenzo Cerulli. Despite its size, due to its very dark surface and relatively large distance from the Sun, it appears very dim when observed from Earth. For this reason, although it is the 5th largest asteroid, it was discovered only in 1910.

Naming

Interamnia was named after the Latin name for Teramo, Italy, where Cerulli worked.

Stats

Diameter (mean): 317 km
Semi-major axis: 3.059 AU
Orbital Period: 5.35 years
Rotation period: 8.727 hrs
Date discovered: 1910.10.2
Class: F
Type: Main-belt Asteroid
(data from JPL Small-Body Database)

Orbit

Interamnia's orbit is slightly more eccentric that that of Hygiea (15% versus 12%) but differs from Hygiea's in its much greater inclination and slightly shorter period. Another difference is that Interamnia's perihelion is located on the opposite side from the perihelia of the "big four", so that Interamnia at perihelion is actually closer to the Sun than Ceres and Pallas are at the same longitude.

Physical characteristics

Although Interamnia is the largest asteroid after the "big four", it is a very little-studied body. There exist very few details of its internal composition or shape, and no lightcurve analysis has yet been done to Interamnia.

Its apparently high bulk density (though subject to much error) suggests an extremely solid body entirely without internal porosity or traces of water.

This also strongly suggests that Interamnia is large enough to have fully withstood all the collisions that have occurred in the asteroid belt since the Solar System was formed.