PALLAS

second largest known asteroid and the second such object to be discovered. It was detected in 1802 by the German astronomer and physician Wilhelm Olbers following the discovery of Ceres, the largest asteroid, the year before. It was named after Pallas Athena, the Greek goddess of wisdom. Pallas measures 608 kilometres (377 miles) in diameter. Its orbital inclination to the plane of the ecliptic (i.e., Earth's orbital plane) is rather large at nearly 35, but its semimajor axis and period are typical for asteroids, at 2.77 astronomical units (414,390,000 km) and 4.61 years, respectively. This places Pallas within the asteroid belt between Mars and Jupiter. Pallas is thought to be spheroidal in shape, because it seems massive enough for gravity to have pulled its constituent material into that shape during formation. Based on studies of its reflecting spectrum, the surface of Pallas appears to be essentially that of the early forming, dark, carbon-rich stony asteroids (carbonaceous chondrites). Pallas differs, however, in having water locked into its surface material (i.e., not in free ice or liquid form) and a higher proportion of magnesium in its stony inclusions. Pallas' albedo is 0.09, somewhat greater than typical carbonaceous chondrite asteroids.