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2 Pallas

This article is about the asteroid. For other uses, see Pallas (disambiguation).

2 Pallas
VLT-SPHERE image of Pallas[a]
Discovery[1]
Discovered byHeinrich Wilhelm Olbers
Discovery date28 March 1802
Designations
(2) Pallas
Pronunciation/ˈpæləs/[2]
Named after
Pallas Athena[3]
Asteroid belt (central)
Pallas family[4]
AdjectivesPalladian (/pæˈleɪdiən/)[5]
Symbol⚴ (historically astronomical, now astrological)
Orbital characteristics[6]
Epoch 13 September 2023
(JD 2453300.5)
Uncertainty parameter 0
Observation arc219 yr
Aphelion3.41 AU (510 million km)
Perihelion2.13 AU (319 million km)
2.77 AU (414 million km)
Eccentricity0.2302
4.611 yr (1,684.0 d)
40.6
0° 12m 46.8s / day
Inclination34.93°
(34.43° to invariable plane)[7]
172.9°
7 March 2023
310.9°
Earth MOID1.2 AU (180 million km)
Proper orbital elements[8]
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
Dimensions(568 km × 532 km × 448 km) ± 12 km[9]
550 km × 516 km × 476 km[10]
511±4 km[11]
513±6 km[9]
512±6 km[10]
Flattening0.21[b]
(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]
0.021 g0
Equatorial escape velocity
324 m/s[9]
7.8132 h[14]
Equatorial rotation velocity
65 m/s[c]
84°±5°[10]
0.155[11]
0.159[15]
B[6][16]
6.49[17] to 10.65
4.13[15]
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 likely a 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 Matthias 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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  1. ^ Cite error: The named reference MPC-object was invoked but never defined (see the help page).
  2. ^ "Pallas". Dictionary.com Unabridged (Online). n.d.
  3. ^ Cite error: The named reference springer was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Ferret was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference oxford was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference jpldata was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Souami_Souchay_2012 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Pallas-POE was invoked but never defined (see the help page).
  9. ^ 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.
  10. ^ a b c Cite error: The named reference Carry2009 was invoked but never defined (see the help page).
  11. ^ 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
  12. ^ Cite error: The named reference surfacecalc was invoked but never defined (see the help page).
  13. ^ a b Cite error: The named reference Baer2011 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference lcdb was invoked but never defined (see the help page).
  15. ^ a b Cite error: The named reference iras was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference tax was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Pasachoff1983 was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference AutoCB-21 was invoked but never defined (see the help page).
  19. ^ 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.
  20. ^ Cite error: The named reference AutoCB-3 was invoked but never defined (see the help page).
  21. ^ Lutz, Harald (28 April 2021). Astrolutz 2022. Books on Demand. ISBN 978-3-7534-7124-2.

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