Global Information2 Pallas information
 VLT-SPHERE image of Pallas[a] | |
| Discovery[1] | |
|---|---|
| Discovered by | Heinrich Wilhelm Olbers |
| Discovery date | 28 March 1802 |
| Designations | |
MPC designation | (2) Pallas |
| Pronunciation | /ˈpæləs/[2] |
Named after | Pallas Athena[3] |
Minor planet category | Asteroid belt (central) Pallas family[4] |
| Adjectives | Palladian (/pæˈleɪdiən/)[5] |
| Symbol |  (historically astronomical, now astrological) |
| Orbital characteristics[6] | |
| Epoch 13 September 2023 (JD 2453300.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 219 yr |
| Aphelion | 3.41 AU (510 million km) |
| Perihelion | 2.13 AU (319 million km) |
Semi-major axis | 2.77 AU (414 million km) |
| Eccentricity | 0.2302 |
Orbital period (sidereal) | 4.611 yr (1,684.0 d) |
Mean anomaly | 40.6 |
Mean motion | 0° 12m 46.8s / day |
| Inclination | 34.93° (34.43° to invariable plane)[7] |
Longitude of ascending node | 172.9° |
Time of perihelion | 7 March 2023 |
Argument of perihelion | 310.9° |
| Earth MOID | 1.2 AU (180 million km) |
| Proper orbital elements[8] | |
Proper semi-major axis | 2.7709176 AU |
Proper eccentricity | 0.2812580 |
Proper inclination | 33.1988686° |
Proper mean motion | 78.041654 deg / yr |
Proper orbital period | 4.61292 yr (1684.869 d) |
Precession of perihelion | −1.335344 arcsec / yr |
Precession of the ascending node | −46.393342 arcsec / yr |
| Physical characteristics | |
| Dimensions | (568 km × 532 km × 448 km) ± 12 km[9] 550 km × 516 km × 476 km[10] |
Mean diameter | 511±4 km[11]
513±6 km[9] 512±6 km[10] |
| Flattening | 0.21[b] |
Surface area | (8.3±0.2)×105 km2 (2020)[c] |
| Volume | (7.06±0.3)×107 km3 (2020)[9] |
| Mass | (2.04±0.03)×1020 kg average est.[9] (2.01±0.13)×1020 kg[d][13] |
Mean density | 2.92±0.08 g/cm3[11] 2.89±0.08 g/cm3[9] 2.57±0.19 g/cm3[13] |
Equatorial surface gravity | ≈0.21 m/s2 (average)[e] 0.022 g |
Equatorial escape velocity | 324 m/s[9] |
Synodic rotation period | 7.8132 h[14] |
Equatorial rotation velocity | 65 m/s[c] |
Axial tilt | 84°±5°[10] |
Geometric albedo | 0.155[11] 0.159[15] |
Spectral type | B[6][16] |
Apparent magnitude | 6.49[17] to 10.65 |
Absolute magnitude (H) | 4.13[15] |
Angular diameter | 0.629″ to 0.171″[f] |
Pallas (minor-planet designation: 2 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 (315 to 320 mi) in diameter, 90–95% the volume of Vesta.
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.[18]
When Pallas was discovered by the German astronomer Heinrich Wilhelm Matthäus Olbers on 28 March 1802, it was considered to be a planet,[19] 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.[20]
The high inclination of the orbit of Pallas results in the possibility of close conjunctions to stars that other solar objects always pass at great angular distance. This resulted in Pallas passing Sirius on 9 October 2022, only 8.5 arcminutes southwards,[21] while no planet can get closer than 30 degrees to Sirius.
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Pallas-POEwas invoked but never defined (see the help page). - ^ a b c d e f Marsset, M, Brož, M, Vernazza, P, et al. (2020). "The violent collisional history of aqueously evolved (2) Pallas" (PDF). Nature Astronomy. 4 (6): 569–576. Bibcode:2020NatAs...4..569M. doi:10.1038/s41550-019-1007-5. hdl:10261/237549. S2CID 212927521.
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Carry2009was invoked but never defined (see the help page). - ^ a b c d P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. Astronomy & Astrophysics 54, A56
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AutoCB-21was invoked but never defined (see the help page). - ^ Hilton, James L. "When did the asteroids become minor planets?". Astronomical Applications Department. US Naval Observatory. Archived from the original on 6 April 2019. Retrieved 27 March 2019.
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AutoCB-3was invoked but never defined (see the help page). - ^ Astrolutz 2022. ISBN 978-3-7534-7124-2.