85 Io

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85 Io
Discovered by C. H. F. Peters
Discovery time September 19, 1865
Other names A899 LA; A899 UA
Group Main belt
Reference date March 6, 2006 (JD 2453800.5)
Longest distance from the Sun 473.341 Gm (3.164 AU)
Shortest distance from the Sun 320.334 Gm (2.141 AU)
Longest distance from the center of its orbital path
("semi-major axis")
396.837 Gm (2.652 AU)
How egg-shaped its orbit is
How long it takes to complete an orbit 1578.081 d (4.32 a)
Average speed 18.12 km/s
Mean anomaly 206.947°
Angle above the reference plane
Longitude of where it comes up through the reference plane 203.440°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
Size and Other Qualities
Measures 180×160×160 km[1][4]
Mass ~3.4×1018 (estimate)
Average density ~1.4 g/cm³ (estimate)[5]
Gravity at its surface ~0.028 m/s² (estimate)
Slowest speed able to escape into space
("escape velocity")
~0.07 km/s (estimate)
How long it takes to turn around one time 0.2864 d (6.875 h) [2]
How much light it reflects 0.067 [3]
Avg. surface temp. ~172 K
max: 272K (-2° C)
Light-band group
("spectral type")
C-type asteroid
True brightness
("absolute magnitude")

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.

Other websites[change | change source]

References[change | change source]

  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).