31 Euphrosyne

31 Euphrosyne
Discovered by J. Ferguson
Discovery date September 1, 1854
Alternative names A907 GP; A918 GB
Minor planet
Main belt
Orbital characteristics
Epoch December 31, 2006 (JD 2454100.5)
Aphelion 577.571 Gm (3.861 AU)
Perihelion 364.755 Gm (2.438 AU)
Semi-major axis 471.163 Gm (3.150 AU)
Eccentricity 0.226
Orbital period 2041.585 d (5.59 a)
Average orbital speed 16.57 km/s
Mean anomaly 14.500°
Inclination 26.316°
Longitude of ascending node 31.238°
Argument of perihelion 61.996°
Physical characteristics
Dimensions 255.9 km
Mass ~1.69×1019 kg [1]
Mean density ~1.9 g/cm³
Equatorial surface gravity ~0.0679 m/s²
Escape velocity ~0.1319 km/s
Rotation period 0.2305 d (5.531 h) [2]
Albedo 0.0543 [3]
Temperature ~159 K
Spectral type C[4]
Absolute magnitude 6.74

31 Euphrosyne (pronounced /juːˈfrɒzɪni/, Greek: Ευφροσύνη) is one of the largest main belt asteroids, discovered by James Ferguson on September 1, 1854. It was the first asteroid found from North America. It is named after Euphrosyne, one of the Charites in Greek mythology.

It is the eighth largest main belt asteroid and contains around 1% of the mass of the entire asteroid belt, but is a very dark body near the belt's outer edge. Consequently Euphrosyne is never visible with binoculars, having a maximum magnitude at the best possible opposition of around +10.2, which is actually fainter than any of the thirty asteroids previously discovered[5].

It is a very little-studied body despite being one of the largest asteroids. It is a typical C-type asteroid with a primitive surface. Its orbit, however, is quite unusual and bears a considerable resemblance to that of 2 Pallas in its high inclination and eccentricity. Whereas Pallas and Eris - the only larger bodies with comparably tilted orbits - have nodes near perihelion and aphelion, Euphrosyne's perihelion lies at the northernmost point of its orbit. During a rare perihelic opposition Euphrosyne is very high in the sky from northern latitudes, but invisble from such countries as New Zealand and Chile.

Its apparently low density suggests that, unlike 10 Hygiea, 704 Interamnia and 52 Europa, Euphrosyne is a loosely-packed rubble pile. Its rotation period is very typical for large asteroids, but nothing is known of its axial tilt.


1. ^ Values of asteroid masses

2. ^ [1]

3. ^ http://www.psi.edu/pds/asteroid/EAR_A_5_DDR_ALBEDOS_V1_1/data/albedos.tab

4. ^ [http://www.agu.org/reference/gephys/4_yoder.pdf Astrometric and Geodetic Properties of Earth and the Solar System]

5. ^ Brightest asteroids

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