85 Io

This article is about an Asteroid. For the satellite of Jupiter, see Io (moon). For other uses, see Io (disambiguation).

85 Io

Discovery
Discovered by	C. H. F. Peters
Discovery date	September 19, 1865
Designations
Named after	Io
Alternate name(s)	A899 LA; A899 UA
Minor planet category	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)
Semi-major axis	396.837 Gm (2.652 AU)
Eccentricity	0.193
Orbital period	1578.081 d (4.32 a)
Average orbital speed	18.12 km/s
Mean anomaly	206.947°
Inclination	11.967°
Longitude of ascending node	203.440°
Argument of perihelion	122.293°
Proper orbital elements
Physical characteristics
Dimensions	180×160×160 km[1][4]
Mass	~3.4×1018 (estimate)
Mean density	~1.4 g/cm³ (estimate)[5]
Equatorial surface gravity	~0.028 m/s² (estimate)
Escape velocity	~0.07 km/s (estimate)
Rotation period	0.2864 d (6.875 h) [2]
Albedo	0.067 [3]
Temperature	~172 K max: 272K (-2° C)
Spectral type	C
Absolute magnitude (H)	7.61

85 Io ( /ˈaɪ.oʊ/ EYE-oh) is a large, dark main-belt asteroid of the C spectral class. It is probably a primitive body composed 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 regular.

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

An Ionian diameter of 178 kilometres was measured from an occultation of a star on December 10, 1995.^[4] Another asteroid occultation of Io (magnitude 13.2) occurred on March 12, 2009, from the eastern USA, with the star 2UCAC 35694429 (magnitude 13.8).

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

Conjunction to sun	stationary, then retrograde	Opposition	Minimal distance (AE)	Maximum brightness (mag)	stationary, then prograde
27. April 2004	31.October 2004	23. December 2004	1,92017 AE	12,3 mag	11. February 2005
3.August 2005	9. . January 2006	5. March 2006	2,14389 AE	11,8 mag	25. April 2006
17.October 2006	26. April 2007	9.June 2007	1,38393 AE	12,1 mag	26.July 2007
7. March 2008	6.October 2008	22.November 2008	1,61470 AE	10,7 mag	9. . January 2009
8.July 2009	17. December 2009	12. February 2010	2,19864 AE	11,1 mag	3. April 2010
21.September 2010	15. March 2011	30. April 2011	1,68623 AE	12,2 mag	20.June 2011
7. . January 2012	31.August 2012	12.October 2012	1,28465 AE	11,1 mag	19.November 2012
9.June 2013	25.November 2013	20. . January 2014	2,13519 AE	10,1 mag	12. March 2014
29.August 2014	10. February 2015	1. April 2015	1,95222 AE	12,2 mag	22.May 2015
22.November 2015	30.June 2016	14.August 2016	1,16222 AE	11,6 mag	17.September 2016
3.May 2017	3.November 2017	26. December 2017	1,95048 AE	10,2 mag	15. February 2018
6.August 2018	13. . January 2019	9. March 2019	2,12957 AE	11,8 mag	28. April 2019
21.October 2019	2.May 2020	14.June 2020	1,34977 AE	12,0 mag	30.July 2020

References

1. J. Torppa et al. Shapes and rotational properties of thirty asteroids from photometric data, Icarus, Vol. 164, p. 346 (2003).
2. PDS lightcurve data
3. Supplemental IRAS Minor Planet Survey
4. 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).
5. G. A. Krasinsky et al. Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).

External links

• shape model deduced from lightcurve

See also

• List of Solar System objects by size