7 Iris

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**7 Iris**
Discovery ^A

Discoverer	John Russell Hind
Discovery date	August 13, 1847
Alternate designations ^B	none
Category	Main belt
Orbital elements ^C
Epoch November 26, 2005 (JD 2453700.5)
Eccentricity (e)	0.231
Semi-major axis (a)	356.798 G m (2.385 AU)
Perihelion (q)	274.259 Gm (1.833 AU)
Aphelion (Q)	439.337 Gm (2.937 AU)
Orbital period (P)	1345.375 d (3.68 a)
Mean orbital speed	19.03 km/s
Inclination (i)	5.527°
Longitude of the ascending node (Ω)	259.727°
Argument of perihelion (ω)	145.440°
Mean anomaly (M)	269.531°
Physical characteristics ^D
Dimensions	225×190×190 km^[1][4]
Mass	1.0×10¹⁹ kg^[2]
Density	2.4 g/cm³
Surface gravity	0.055 m/s²
Escape velocity	0.11 km/s
Rotation period	0.2975 d ^[3]
Spectral class	S-type asteroid
Absolute magnitude	5.51
Albedo (geometric)	0.277 ^[1]
Mean surface temperature	~171 K max: 275 K (+2° C)

7 Iris (eye'-rəs (key)) is one of the largest main belt asteroids.

Size comparison: the first 10 asteroids profiled against Earth's Moon. Iris is fourth from the right.

1 Discovery and name
2 Characteristics
3 Aspects
4 References
5 External links

[edit] 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.

[edit] 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 hemisphere 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.

[edit] Aspects

Stationary, retrograde	Opposition	Distance to Earth (AU)	Maximum brightness (mag)	Stationary, prograde	Conjunction to Sun
April 12, 2005	June 3, 2005	1.81674	9.2	July 27, 2005	January 24, 2006
October 10, 2006	November 14, 2006	0.85211	6.6	December 16, 2006	August 25, 2007
February 14, 2008	April 9, 2008	1.85457	9.4	May 29, 2008	November 21, 2008
May 15, 2009	July 4, 2009	1.55566	8.7	August 24, 2009	March 19, 2010
December 8, 2010	January 23, 2011	1.16806	7.9	March 6, 2011	September 28, 2011
March 11, 2012	May 4, 2012	1.92914	9.5	June 26, 2012	December 16, 2012
July 1, 2013	August 16, 2013	1.16690	7.9	September 28, 2013	June 16, 2014
January 12, 2015	March 6, 2015	1.56393	8.9	April 21, 2015	October 24, 2015
April 7, 2016	May 29, 2016	1.84861	9.2	July 22nd, 2016	January 16, 2017
September 22nd, 2017	October 29, 2017	0.85325	6.9	November 28, 2017	August 16, 2018
February 9, 2019	April 5, 2019	1.82359	9.4	May 25, 2019	November 17, 2019
May 8, 2020	June 27, 2020	1.61521	8.8	August 18, 2020	March 6, 2021

[edit] References

Supplemental IRAS Minor Planet Survey
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).

[edit] External links

Minor planets
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For other objects and regions, see: asteroid groups and families, binary asteroids, asteroid moons and the Solar system For a complete listing, see: List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.