| Minorplanet: | yes |
| Background: |
|
| 85 Io | |
| Discovered: | 19 September 1865 |
| Mpc Name: | (85) Io |
| Alt Names: | A899 LAA899 UA |
| Pronounced: | [1] |
| Adjective: | Ionian |
| Orbit Ref: |   |
| Epoch: | 4 September 2017 (JD 2458000.5) |
| Uncertainty: | 0 |
| Observation Arc: | 151.35 yr (55,280 days) |
| Perihelion: | 2.1379 AU |
| Semimajor: | 2.6529 AU |
| Eccentricity: | 0.1941 |
| Period: | 4.32 yr (1,578 days) |
| Mean Motion: | / day |
| Inclination: | 11.961° |
| Asc Node: | 203.12° |
| Arg Peri: | 123.11° |
| Dimensions: | 180 × 160 × 160 km |
| Mass: | (5.034 ± 0.999/1.406) kg |
| Density: | 2.14 ± 0.425/0.598 g/cm3 |
| Rotation: | 0.2864 d (6.875 h) |
| Albedo: | 0.0666 ± 0.003 |
| Abs Magnitude: | 7.96 |
85 Io is a carbonaceous asteroid in the central region of the asteroid belt, approximately 170 kilometers in diameter. It is an identified Eunomian interloper.
It was discovered by C. H. F. Peters on 19 September 1865, and named after Io, a lover of Zeus in Greek mythology. 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.
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. This gives an axial tilt of about 125° or 115°, respectively. Its shape is quite regular.
In the SMASS classification, Io is a carbonaceous C-type asteroid, which means that it is probably a primitive body composed of carbonates. Like 141 Lumen it is an interloper that orbits within the Eunomia asteroid family but it is not related to the shattered parent body.
An Ionian diameter of 178 kilometres was measured from an occultation of a star on 10 December 1995. Another asteroid occultation of Io (magnitude 13.2) occurred on 12 March 2009, from the eastern United States, with the star 2UCAC 35694429(magnitude 13.8).[2]
| 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 |