2 Pallas

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**2 Pallas Image:Pallas symbol.svg**
Discovery ^A

Discoverer	Heinrich Wilhelm Olbers
Discovery date	March 28, 1802
Alternate designations ^B	none
Category	Pallas family
Orbital elements ^C
Epoch November 26, 2005 (JD 2453700.5)
Eccentricity (e)	0.231
Semi-major axis (a)	414.784 G m (2.773 AU)
Perihelion (q)	319.143 Gm (2.133 AU)
Aphelion (Q)	510.425 Gm (3.412 AU)
Orbital period (P)	1686.333 d (4.62 a)
Mean orbital speed	17.65 km/s
Inclination (i)	34.841°
Longitude of the ascending node (Ω)	173.152°
Argument of perihelion (ω)	310.448°
Mean anomaly (M)	92.795°
Physical characteristics ^D
Dimensions	570×525×500 km ^[4][5]
Mass	2.2×10²⁰ kg ^[1][6]
Density	2.8 g/c m³
Surface gravity	0.18 m/s²
Escape velocity	0.32 km/s
Rotation period	0.32555 d
Spectral class	B-type asteroid
Absolute magnitude	4.13
Albedo (geometric)	0.159 ^[2]
Mean surface temperature	~164 K max: ~265 K (-8° C)

2 Pallas (pal'-əs (key), Greek Παλλάς) is an asteroid located in the asteroid belt region of the solar system and was the second to be discovered. It was found and named by astronomer Heinrich Wilhelm Matthäus Olbers on March 28, 1802. Pallas is the third most massive object in the asteroid belt and is estimated to contain 7% of the region's entire mass.

Pallas, as well as 1 Ceres, 3 Juno and 4 Vesta, were once considered planets until the discovery of many other asteroids led to re-classifications. It is possible that Pallas may be classified as a dwarf planet in the future, but only if it is found that its shape is consistent with hydrostatic equilibrium.

1 Name
2 Characteristics
3 Observations
4 Trivia
5 Aspects
6 External links
7 References
8 See also

[edit] Name

The asteroid is named after Pallas, the daughter of Triton and friend of Athena in Greek mythology. There are several male characters of the same name in Greek mythology, but the first asteroids were invariably given female names.

According to the OED, the adjectival form of Pallas is Palladian. Pallas' astronomical and astrological symbol is Image:Pallas symbol.svg or sometimes Image:2 Pallas (1).png .

[edit] Characteristics

Size comparison: the first 10 asteroids profiled against Earth's Moon. Pallas is at second left.

Pallas is the third largest object in the asteroid belt, similar to 4 Vesta in volume (to within uncertainty), but significantly less massive.

Pallas has unusual dynamical parameters for such a large body. Its orbit is highly inclined and somewhat eccentric despite being located at the same distance from the sun as the central part of the Main belt.

Furthermore, its axial tilt is very high, being around 60° (in fact estimates vary from 56° to 81°) ^[4][7][9]. This means that, every palladian summer and winter, large parts of the surface are in constant sunlight or constant darkness for a time of the order of an Earth year. Consensus has not been reached as to whether Pallas' rotation is prograde or retrograde. The most recent analysis of lightcurves indicates that the pole points towards ecliptic coordinates (β, λ) = (-12°, 35°) or (43°, 193°) with a 10° uncertainty ^[9]. This gives axial tilts of 57° or 65°, respectively.

There are indications that the surface composition of Pallas is very similar to the Renazzo carbonaceous chondrite (CR) meteorites ^[8].

[edit] Observations

Pallas has been observed occulting a star several times, including the best observed of all asteroid occultation events on May 29, 1983, when careful occultation timing measurements were taken by 140 observers. These have helped determine an accurate diameter ^[5]. During the occultation of May 29, 1979 the discovery of a possible tiny satellite with a diameter of ~1 km was reported. However, it has not been confirmed. In 1980, speckle interferometry was reported as indicating a much larger satellite with a diameter of 175 km, but the existence of the satellite was later refuted. ^[3]

Radio signals from spacecraft in orbit around Mars and/or on its surface have been used to estimate the mass of Pallas from the tiny perturbations induced by it onto the motion of Mars ^[1].

There have not been any telescopic observations of Pallas that have resolved any features on its disk. Pallas has not yet been visited by a spacecraft, but if the Dawn probe is successful in studying 1 Ceres and 4 Vesta, its mission may be extended to Pallas.

[edit] Trivia

The chemical element palladium (atomic number 46) was named after Pallas.

[edit] Aspects

Stationary, retrograde	Opposition	Distance to Earth (AU)	Maximum brightness (mag)	Stationary, prograde	Conjunction to Sun
February 14, 2005	March 23, 2005	1.37020	7.1	May 7, 2005	November 18, 2005
May 2, 2006	July 1, 2006	2.52251	9.5	August 24, 2006	February 1, 2007
July 6, 2007	September 3, 2007	2.25303	8.8	October 22, 2007	March 29, 2008
October 28, 2008	December 4, 2008	1.56731	8.0	January 21, 2009	September 12, 2009
March 24, 2010	May 3, 2010	1.94004	8.6	July 2, 2010	December 22, 2010
May 25, 2011	July 29, 2011	2.54744	9.5	September 16, 2011	February 22, 2012
August 9, 2012	September 24, 2012	1.96443	8.3	November 17, 2012	May 9, 2013
January 5, 2014	February 20, 2014	1.23636	7.0	March 23, 2014	October 25, 2014
April 19, 2015	June 11, 2015	2.38719	9.4	August 7, 2015	January 19, 2016
June 18, 2016	August 20, 2016	2.40255	9.2	October 7, 2016	March 14, 2017
September 24, 2017	October 27, 2017	1.70519	8.2	December 23, 2017	August 5, 2018
March 4, 2019	April 8, 2019	1.57083	7.8	June 1, 2019	December 2, 2019
May 10, 2020	July 12, 2020	2.55643	9.6	September 1, 2020	February 9, 2021

[edit] External links

[edit] References

E. V. Pitjeva, Estimations of Masses of the Largest Asteroids and the Main Asteroid Belt From Ranging to Planets, Mars Orbiters And Landers Solar System Resarch, Vol. 39 pp. 176 (2005).
Supplemental IRAS Minor Planet Survey
Other Reports of Asteroid Companions, compiled by Wm. Robert Johnston
J. D. Drummond and W. J. Cocke Triaxial ellipsoid dimensions and rotational pole of 2 Pallas from two stellar occultations, Icarus, Vol. 78, pp. 323 (1989).
D. W. Dunham et al The size and shape of (2) Pallas from the 1983 occultation of 1 Vulpeculae, The Astronomical Journal, Vol. 99, pp. 1636 (1990).
E. Goffin New determination of the mass of (2) Pallas, Astronomy and Astrophysics, Vol. 365, pp. 627 (2001).
D. L. Mitchell et al Radar observations of asteroids 1 Ceres, 2 Pallas, and 4 Vesta, Icarus, Vol. 124, pp. 113 (1996).
Sato et al Absorption bands near three micrometers in diffuse reflectance spectra of carbonaceous chondrites: Comparison with asteroids, Meteoritics and Planetary Science, Vol. 32, pp. 503 (1997).
J. Torppa et al Shapes and rotational properties of thirty asteroids from photometric data, Icarus, Vol. 164, p. 346 (2003).
James L. Hilton, U.S. Naval Observatory Ephemerides of the Largest Asteroids The Astronomical Journal, Vol. 117 pp. 1077 (1999).

[edit] See also

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Vulcanoids \| Near-Earth asteroids \| Main belt \| Jupiter Trojans \| Centaurs \| Damocloids \| Comets \| Trans-Neptunians (Kuiper belt · Scattered disc · Oort cloud)
For other objects and regions, see: asteroid groups and families, binary asteroids, asteroid moons and the Solar system For a complete listing, see: List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.