7 Iris
Encyclopedia : 7 : 7I : 7IR : 7 Iris
| Orbital elements | |
|---|---|
| Eccentricity (orbit)>e | |
| Inclination>i | ° |
| Perihelion>q |
|
| Argument of perihelion>ω | ° |
| Semi-major axis>a | AU |
| Longitude of the ascending node>ω | ° |
| Aphelion>Q |
|
| Mean anomaly>M | ° |
| Orbital period>P | years |
| Mean motion>n | °/day |
| Time of perihelion passage>TP | |
Discovery and name
It was the seventh asteroid discovered, on August 13, 1847 by J. R. Hind from London, UK. It was Hind's first asteroid discovery.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
Lightcurve analysis indicates a somewhat angular shape and that Iris' pole points towards ecliptic coordinates (β, λ) = (10°, 20°) with a 10° uncertainty [4]. This gives an axial tilt of 85°, so that on almost a whole hemisphee of Iris, the sun does not set during summer, and does not rise during winter. On an airless body this gives rise to very large temperature differences.Iris' surface likely exhibits albedo differences, with possibly a large bright area on the northern hemisphere[5].
The surface of Iris is overall very bright and is probably a mixture nickel-iron metals and magnesium- and iron-silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering[6], so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites[7].
Iris was observed occulting a star on May 26, 1995 and later on July 25, 1997. Both observations gave a diameter of about 200 km.
Aspects
References
- [E. V. Pitjeva, Estimations of Masses of the Largest Asteroids and the Main Asteroid Belt From Ranging to Planets, Mars Orbiters And Landers] Solar System Resarch, Vol. 39 pp. 176 (2005).
- [Planetary Data System Small Bodies Node, lightcurve parameters]
- [M. Kaasalainen et al Models of twenty asteroids from photometric data], Icarus, Vol. 159, p. 369 (2002).
- [M. Hoffmann & E. H. Geyer Spots on 4-VESTA and 7-IRIS - Large Areas or Little Patches], Astronomy & Astrophysics Supplement, Vol. 101, p. 621 (1993).
- [Y. Ueda et al Surface Material Analysis of the S-type Asteroids: Removing the Space Weathering Effect from Reflectance Spectrum], 34th Annual Lunar and Planetary Science Conference, March 17-21, 2003, League City, Texas, abstract no.2078 (2003).
- [F. Migliorini et al (7) Iris: a possible source of ordinary chondrites?], Astronomy & Astrophysics, Vol. 321, p. 652 (1997).
External links
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