2nd Largest Asteroid, 2 Pallas

An ultraviolet image of Pallas showing flattened shape taken by the Hubble Telescope.






Discovery

Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered (after Ceres), and one of the largest.

On March 28, 1802, astronomer Heinrich Wilhelm Matthäus Olbers was attempting to locate Ceres when he noticed another moving object in the vicinity. This was the asteroid Pallas, coincidentally passing near Ceres at the time.

When Pallas was discovered, it was counted as a planet. The discovery of many more asteroids after 1845 eventually led to their re-classification.

Naming

2 Pallas is named after Pallas Athena, an alternate name for the goddess Athena. In some mythologies Athena killed Pallas, then adopted her friend's name out of mourning. (There are several male characters of the same name in Greek mythology, but the first asteroids were invariably given female names).

Stats

Diameter: 545 km
Semi-major axis: 2.772 AU
Orbital Period: 4.62 years
Rotation period: 7.813 hrs
Date discovered: 1802.3.28
Class: B
Type: Main-belt Asteroid
(data from JPL Small-Body Database)

Orbit

Pallas's orbit is highly inclined and somewhat eccentric, despite being at the same distance from the Sun as the central part of the asteroid belt.

Pallas's axial tilt is very high, about 78±13°, based on data from the Hubble Space Telescope obtained in 2007, as well as the observations by the Keck telescope in 2003–2005. This means that, every Palladian summer and winter, large parts of the surface are in constant sunlight or constant darkness for a time of the order of an Earth year.

Surface Characteristics

Based on spectroscopic observations, the primary component of the Palladian surface material is a silicate that is low in iron and water.

Pallas is believed to have undergone at least some degree of thermal alteration and partial differentiation, which suggests that it was a protoplanet.

During the planetary formation stage of the Solar System, objects grew in size through an accretion process to approximately this size. Many of these objects were incorporated into larger bodies, which became the planets, while others were destroyed in collisions with other protoplanets. Pallas is likely one of the survivors from this early stage of planetary formation.