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85 Io
Discovered by C. H. F. Peters
Discovery date September 19, 1865
A899 LA; A899 UA
Main belt
Orbital characteristics
Epoch March 6, 2006 (JD 2453800.5)
Aphelion 473.341 Gm (3.164 AU)
Perihelion 320.334 Gm (2.141 AU)
396.837 Gm (2.652 AU)
Eccentricity 0.193
1578.081 d (4.32 a)
18.12 km/s
Inclination 11.967°
Physical characteristics
Dimensions 180×160×160 km[1][4]
Mass ~3.4×1018 (estimate)
Mean density
~1.4 g/cm³ (estimate)[5]
~0.028 m/s² (estimate)
~0.07 km/s (estimate)
0.2864 d (6.875 h) [2]
Albedo 0.067 [3]
Temperature ~172 K
max: 272K (-2° C)
Spectral type
C-type asteroid

85 Io is a big, dark Main belt asteroid of the C spectral class. It is probably a primitive body made of carbonates. Like 70 Panopaea it orbits within the Eunomia asteroid family but it is not related to the shattered parent body.

Io is a retrograde rotator, with its pole pointing towards one of ecliptic coordinates (β, λ) = (-45°, 105°) or (-15°, 295°) with a 10° uncertainty[1]. This gives an axial tilt of about 125° or 115°, respectively. Its shape is quite spherical.

It was found by C. H. F. Peters on September 19, 1865 and named after Io, a lover of Zeus in Greek mythology.

A diameter of 178 kilometres was measured from an occultation of a star on December 10, 1995 [4].

Io is also the name of the volcanic moon of Jupiter. With a two-digit number and a two-letter name, 85 Io has the shortest designation of all minor planets.

  1. PDS lightcurve data
  2. A. Erikson Photometric observations and modelling of the asteroid 85 Io in conjunction with data from an occultation event during the 1995-96 apparition, Planetary and Space Science, Vol. 47, p. 327 (1999).
  3. G. A. Krasinsky et al. Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
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