Heinrich Wilhelm Matthias Olbers
Heinrich Wilhelm Matthias Olbers was a German astronomer. He found a convenient method of calculating the orbit of comets, and in 1802 and 1807, discovered the second and the fourth asteroids Pallas and Vesta.
Lithograph by Rudolph Suhrlandt
Olbers monument in Bremen by Carl Johann Steinhäuser (1850)
Abhandlung über die leichteste und bequemste Methode die Bahn eines Cometen zu berechnen, 1797
Pallas is the third-largest asteroid in the Solar System by volume and mass. It is the second asteroid to have been discovered, after Ceres, and is a likely remnant protoplanet. Like Ceres, it is believed to have a mineral composition similar to carbonaceous chondrite meteorites, though significantly less hydrated than Ceres. It is 79% the mass of Vesta and 22% the mass of Ceres, constituting an estimated 7% of the mass of the asteroid belt. Its estimated volume is equivalent to a sphere 507 to 515 kilometers in diameter, 90–95% the volume of Vesta.
High-resolution images of the north (at left) and south (at right) hemispheres of Pallas, made possible by the Adaptive-Optics (AO)-fed SPHERE imager on the Very Large Telescope (VLT) in 2020. Two large impact basins could have been created by asteroid family–forming impacts. The bright spot in the southern hemisphere is reminiscent of the salt deposits on Ceres.
Relative sizes of the four largest asteroids. Pallas is second from right.
An ultraviolet image of Pallas showing its flattened shape, taken by the Hubble Space Telescope in 2007
Objects considered for dwarf planet status under the IAU's 2006 draft proposal on the definition of a planet. Pallas is second from the right, bottom row.
