4 Vesta - Physical Characteristics

Physical Characteristics

Vesta is the second-most-massive body in the asteroid belt, though only 28% as massive as Ceres. The surface area is approximately the same as that of Pakistan. Vesta orbits in the inner asteroid belt interior to the Kirkwood gap at 2.50 AU. It has a differentiated interior, and is similar to 2 Pallas in volume (to within uncertainty) but about 25% more massive.

Vesta's shape is close to a gravitationally relaxed oblate spheroid, but the large concavity and protrusion at the southern pole (see 'Surface features' below) combined with a mass less than 5×1020 kg precluded Vesta from automatically being considered a dwarf planet under International Astronomical Union (IAU) Resolution XXVI 5. Vesta may be listed as a dwarf planet in the future, if it is convincingly determined that its shape, other than the large impact basin at the southern pole, is due to hydrostatic equilibrium.

Its rotation is relatively fast for an asteroid (5.342 h) and prograde, with the north pole pointing in the direction of right ascension 20 h 32 min, declination +48° (in the constellation Cygnus) with an uncertainty of about 10°. This gives an axial tilt of 29°.

Temperatures on the surface have been estimated to lie between about −20 °C with the Sun overhead, dropping to about −190 °C at the winter pole. Typical daytime and nighttime temperatures are −60 °C and −130 °C, respectively. This estimate is for 6 May 1996, very close to perihelion, while details vary somewhat with the seasons.