31 Euphrosyne

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31 Euphrosyne
Discovered byJ. Ferguson
Discovery dateSeptember 1, 1854
Other namesA907 GP; A918 GB
CategoryMain belt
Reference date December 31, 2006 (JD 2454100.5)
Longest distance from the Sun577.571 Gm (3.861 AU)
Shortest distance from the Sun364.755 Gm (2.438 AU)
Longest distance from the center of its orbital path
("semi-major axis")
471.163 Gm (3.150 AU)
How long it takes to complete an orbit2041.585 d (5.59 a)
Average speed16.57 km/s
Mean anomaly14.500°
Angle above the reference plane
Size and other qualities
Measurements255.9 km
Mass~1.69×1019 kg [1]
Average density~1.9 g/cm³
Surface gravity~0.0679 m/s²
Escape velocity~0.1319 km/s
Rotation period0.2305 d (5.531 h) [2]
How much light it reflects0.0543 [3]
Avg. surface temp.~159 K
Spectral typeC[4]
True brightness
("absolute magnitude")

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. Because of that, 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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