|
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7 Iris
| Discovery A |
| Discoverer |
John Russell Hind |
| Discovery date |
August 13, 1847 |
Alternate
designations |
none B |
| Category |
Main belt |
| Orbital elements C D |
|
Epoch July 14, 2004 (JD 2453200.5)
|
| Eccentricity (e) |
0.230 |
| Semi-major axis (a) |
357.019 Gm (2.387 AU) |
| Perihelion (q) |
274.729 Gm (1.836 AU) |
| Aphelion (Q) |
439.310 Gm (2.937 AU) |
| Orbital period (P) |
1346.628 d (3.69 a) |
| Mean orbital speed |
19.28 km/s |
| Inclination (i) |
5.523° |
Longitude of the
ascending node (Ω)) |
259.766° |
Argument of
perihelion (ω) |
145.406° |
| Mean anomaly (M) |
135.770° |
| Physical characteristics |
| Dimensions |
199.8 km |
| Mass |
8.4—1018 kg |
| Density |
2 ? g/cm³ |
| Surface gravity |
0.0558 m/s² |
| Escape velocity |
0.1056 km/s |
| Rotation period |
0.2975 d 1 |
| Spectral class |
S-type asteroid |
| Absolute magnitude |
5.51 |
| Albedo |
0.277 2 |
Mean surface
temperature |
~171 K |
Size comparison: the first 10 asteroids profiled against Earth's Moon. From left to right, 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 5 Astraea, 6 Hebe, 7 Iris, 8 Flora, 9 Metis, and 10 Hygiea. [Source]
It was the seventh asteroid discovered, on August 13, 1847 by J. R. Hind from London, UK. It was Hinds' first asteroid discovery.
Name
Iris was named after the rainbow goddess Iris of Greek mythology, sister of the Harpies and messenger of the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as she was spotted following 3 Juno (Juno is the Roman equivalent of Hera) by less than an hour of right ascension.
According to the OED, the correct adjectival form of the name is Iridian.
Characteristics
Iris was observed occulting a star on May 26, 1995 and later on July 25, 1997. Both observations give a diameter of about 200 km.
The surface of Iris is very bright and is probably a mixture nickel-iron metals and magnesium- and iron-silicates.
Aspects
| Stationary, retrograde |
Opposition |
Distance to
Earth (AU) |
Maximum
brightness (mag) |
Stationary, prograde |
Conjunction to Sun |
| April 12th, 2005 |
June 3rd, 2005 |
1.81674 |
9.2 |
July 27th, 2005 |
January 24th, 2006 |
| October 10th, 2006 |
November 14th, 2006 |
0.85211 |
6.6 |
December 16th, 2006 |
August 25th, 2007 |
| February 14th, 2008 |
April 9th, 2008 |
1.85457 |
9.4 |
May 29th, 2008 |
November 21st, 2008 |
| May 15th, 2009 |
July 4th, 2009 |
1.55566 |
8.7 |
August 24th, 2009 |
March 19th, 2010 |
| December 8th, 2010 |
January 23rd, 2011 |
1.16806 |
7.9 |
March 6th, 2011 |
September 28th, 2011 |
| March 11th, 2012 |
May 4th, 2012 |
1.92914 |
9.5 |
June 26th, 2012 |
December 16th, 2012 |
| July 1st, 2013 |
August 16th, 2013 |
1.16690 |
7.9 |
September 28th, 2013 |
June 16th, 2014 |
| January 12th, 2015 |
March 6th, 2015 |
1.56393 |
8.9 |
April 21st, 2015 |
October 24th, 2015 |
| April 7th, 2016 |
May 29th, 2016 |
1.84861 |
9.2 |
July 22nd, 2016 |
January 16th, 2017 |
| September 22nd, 2017 |
October 29th, 2017 |
0.85325 |
6.9 |
November 28th, 2017 |
August 16th, 2018 |
| February 9th, 2019 |
April 5th, 2019 |
1.82359 |
9.4 |
May 25th, 2019 |
November 17th, 2019 |
| May 8th, 2020 |
June 27th, 2020 |
1.61521 |
8.8 |
August 18th, 2020 |
March 6th, 2021 |
Links
Discovery of Iris", MNRAS 7 (1847) 299
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The minor planets
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Centaurs | Damocloids | Comets | Trans-Neptunians (Kuiper belt | Scattered disc | Oort cloud)
For other objects and regions, see: Binary asteroids, Asteroid moons and the Solar system
For a complete listing, see: List of asteroids. For pronunciation, see: Pronunciation of asteroid names.
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