31 Euphrosyne

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31 Euphrosyne
Discovery
Discovered by J. Ferguson
Discovery date September 1, 1854
Designations
Alternative names A907 GP; A918 GB
Minor planet category 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]

31 Euphrosyne is one of the biggest main belt asteroids, found 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 biggest 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 farther 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 found.[5]

It has not been studied a lot despite being one of the biggest asteroids. It is a normal C-type asteroid with a primitive surface. Its orbit, however, is quite unusual. It's orbit is similar to that of 2 Pallas in its high inclination and eccentricity. Whereas Pallas and Eris - the only bigger 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 invisible 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 (an asteroid that has been broken apart by a collision with all the pieces pulled together by gravity). Its rotation period is very common for big asteroids, but nothing is known of its axial tilt.

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