2 Pallas

Pallas (minor-planet designation: 2 Pallas) is the second asteroid to have been discovered, after 1 Ceres. Like Ceres, it is believed to have a mineral composition similar to carbonaceous chondrite meteorites, though significantly less hydrated than Ceres. It is the third-largest asteroid in the Solar System by both volume and mass, and is a likely remnant protoplanet. It is 79% the mass of 4 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 (315 to 320 mi) in diameter, 90–95% the volume of Vesta.

2 Pallas
VLT-SPHERE image of Pallas[1]
Discovery[2]
Discovered byHeinrich Wilhelm Olbers
Discovery date28 March 1802
Designations
(2) Pallas
Pronunciation/ˈpæləs/[3]
Named after
Pallas Athena
(Greek goddess)[4]
asteroid belt · (central)
Pallas family[5]
AdjectivesPalladian /pæˈldiən/[6]
Orbital characteristics[7]
Epoch 21 January 21 2022 (JD 2459600.5)
Uncertainty parameter 0
Observation arc217 yr
Aphelion3.41 AU (510 Gm)
Perihelion2.13 AU (319 Gm)
2.77 AU (414 Gm)
Eccentricity0.23
4.613 yr (1,684.9 d)
229.5
0° 12m 46.8s / day
Inclination34.93°
(34.43° to invariable plane[8])
172.9°
310.7°
Proper orbital elements[9]
2.7709176 AU
0.2812580
33.1988686°
78.041654 deg / yr
4.61292 yr
(1684.869 d)
Precession of perihelion
−1.335344 arcsec / yr
Precession of the ascending node
−46.393342 arcsec / yr
Physical characteristics
Dimensionsc/a = 0.79±0.03[10]
568 ±12 km × 532 ±12 km × 448 ±12 km[11]
550 km × 516 km × 476 km[12]
Mean diameter
511±4[10]
513±6 km[11]
512±6 km[12]
(8.3±0.2)×105 km2 (2020)[lower-alpha 1][13]
Volume(7.1±0.3)×107 km3 (2020)[lower-alpha 1][14]
Mass(2.04±0.03)×1020 kg average est.[11]
(2.01±0.13)×1020 kg[lower-alpha 2][15]
Mean density
2.92±0.08 g/cm3[10]
2.89±0.08 g/cm3[11]
2.57±0.19 g/cm3[15]
Equatorial surface gravity
≈0.21 m/s2 (average)[lower-alpha 3]
0.022 g
Equatorial escape velocity
324 m/s[11]
7.8132 h[16]
Equatorial rotation velocity
65 m/s[lower-alpha 1]
84°±[12]
0.155[10]
0.159[17]
B[7][18]
6.49[19] to 10.65
4.13[17]
0.629″ to 0.171″[20]

During the planetary formation era of the Solar System, objects grew in size through an accretion process to approximately the size of Pallas. Most of these 'protoplanets' were incorporated into the growth of larger bodies, which became the planets, whereas others were ejected by the planets or destroyed in collisions with each other. Pallas, Vesta and Ceres appear to be the only intact bodies from this early stage of planetary formation to survive within the orbit of Neptune.[21]

When Pallas was discovered by the German astronomer Heinrich Wilhelm Matthäus Olbers on 28 March 1802, it was counted as a planet,[22] as were other asteroids in the early 19th century. The discovery of many more asteroids after 1845 eventually led to the separate listing of 'minor' planets from 'major' planets, and the realization in the 1950s that such small bodies did not form in the same way as (other) planets led to the gradual abandonment of the term 'minor planet' in favor of 'asteroid' (or, for larger bodies such as Pallas, 'planetoid').

With an orbital inclination of 34.8°, Pallas's orbit is unusually highly inclined to the plane of the asteroid belt, making Pallas relatively inaccessible to spacecraft, and its orbital eccentricity is nearly as large as that of Pluto.[23]


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