7 Iris

Iris was discovered on 13 August 1847, by J. R. Hind from London, UK. It was Hind's first asteroid discovery and the seventh asteroid to be discovered overall. It was named after the rainbow goddess Iris in Greek mythology, who was a messenger to the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as Iris was spotted following 3 Juno by less than an hour of right ascension (Juno is the Roman equivalent of Hera).

Iris's original symbol was a rainbow and a star: 16px or more simply 16px. It is in the pipeline for Unicode 17.0 as U+1CEC1 𜻁 (12px).{{cite web |url=https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf |title=Unicode request for historical asteroid symbols |last1=Bala |first1=Gavin Jared |last2=Miller |first2=Kirk |date=18 September 2023 |website=unicode.org |publisher=Unicode |access-date=26 September 2023 |quote=}}{{cite web |url=https://unicode.org/alloc/Pipeline.html |title=Proposed New Characters: The Pipeline |author=Unicode |date= |website=unicode.org |publisher=The Unicode Consortium |access-date=6 November 2023 |quote=}}

Image:Moon and Asteroids 1 to 10.svg. Iris is fourth from the right.]]

Iris is an S-type asteroid. The surface is bright and is probably a mixture of nickel-iron metals and magnesium- and iron-silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering,{{Cite conference |last1=Ueda |first1=Y. |last2=Miyamoto |first2=M. |last3=Mikouchi |first3=T. |last4=Hiroi |first4=T. |date=March 2003 |title=Surface Material Analysis of the S-type Asteroids: Removing the Space Weathering Effect from Reflectance Spectrum |conference=34th Annual Lunar and Planetary Science Conference |pages=2078 |bibcode=2003LPI....34.2078U}} so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.{{cite journal| bibcode=1997A&A...321..652M| first1= F.|last1= Migliorini| title=(7) Iris: a possible source of ordinary chondrites?| journal=Astronomy & Astrophysics| volume= 321| pages=652| date=1997| first2=A.|last2=Manara|first3=A.| last3=Cellino|first4=M.| last4=Di Martino|first5=V.| last5=Zappala|display-authors=1}}

Among the S-type asteroids, Iris ranks fifth in mean diameter after Eunomia, Juno, Amphitrite and Herculina. Its shape is consistent with an oblate spheroid with a large equatorial excavation, suggesting it is a remnant planetesimal. No collisional family can be associated with Iris, likely because the excavating impact occurred early in the history of the Solar System, and the debris has since dispersed.

File:7Iris-LB1-richfield-mag10.jpg 10.1)]]

Iris's bright surface and small distance from the Sun make it the fourth-brightest object in the asteroid belt after Vesta, Ceres, and Pallas. It has a mean opposition magnitude of +7.8, comparable to that of Neptune, and can easily be seen with binoculars at most oppositions. At typical oppositions it marginally outshines the larger though darker Pallas.{{cite web|last=Odeh |first=Moh'd |url=http://jas.org.jo/ast.html |title=The Brightest Asteroids |publisher=Jordanian Astronomical Society |access-date=2007-07-16 |archive-url=https://web.archive.org/web/20070813224051/http://www.jas.org.jo/ast.html |archive-date=13 August 2007 |url-status=dead }} But at rare oppositions near perihelion Iris can reach a magnitude of +6.7 (last time on 31 October 2017, reaching a magnitude of +6.9), which is as bright as Ceres ever gets.

A study by Hanus et al. using data from the VLT's SPHERE instrument names eight craters 20 to 40 km in diameter, and seven recurring features of unknown nature that remain nameless due to a lack of consistency and their occurrence on the edge of Iris. The names are Greek names of colors, corresponding to the rainbow as the sign of Iris. It is unknown whether these names are under consideration by the IAU. The other 7 features are labeled A through G.

Iris has a rotational period of 7.14 hours. Iris's north pole points towards the ecliptic coordinates (λ, β) estimated to be (18°, +19°) with a 4° uncertainty (Viikinkoski et al. 2017) or (19°, +26°) with a 3° uncertainty (Hanuš et al. 2019). This gives an axial tilt of 85°,{{cite book|last=Pearson|first=Richard |title=The History of Astronomy|year=2020|isbn=9780244866501|page=349|publisher=Lulu.com }} so that on much of each hemisphere, 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.

Image:IrisOrbit.png

Iris was observed occulting a star on 26 May 1995, and later on 25 July 1997. Both observations gave a diameter of about 200 km.

In February 2024, water molecules were discovered on 7 Iris, alongside 20 Massalia, marking the first time water molecules were detected on asteroids.{{cite journal|last1=Arredondo|first1=Anicia|last2=McAdam|first2=Margaret M.|last3=Honniball|first3=Casey I.|last4=Becker|first4=Tracy M.|last5=Emery|first5=Joshua P.|last6=Rivkin|first6=Andrew S.|last7=Takir|first7=Driss|last8=Thomas|first8=Cristina A.|date=12 February 2024|title=Detection of Molecular H₂O on Nominally Anhydrous Asteroids|journal=The Planetary Science Journal|volume=5|issue=2|page=37|doi=10.3847/PSJ/ad18b8|doi-access=free |bibcode=2024PSJ.....5...37A }}{{cite news|last=Gamillo|first=Elizabeth|title=Water molecules identified on asteroids for the first time|url=https://www.astronomy.com/science/water-molecules-identified-on-asteroids-for-the-first-time/|website=Astronomy|date=14 February 2024|accessdate=27 March 2024}}

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{{reflist}}

• {{cite journal |doi=10.1006/icar.2002.6907 |url=http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf |archive-url=https://web.archive.org/web/20041015112635/https://www.rni.helsinki.fi/~mjk/IcarPIII.pdf|archive-date=15 October 2004 |title=Models of Twenty Asteroids from Photometric Data |date=2002 |last1=Kaasalainen |first1=M. |last2=Torppa |first2=J. |last3=Piironen |first3=J. |journal=Icarus |volume=159 |issue=2 |pages=369–395 |bibcode=2002Icar..159..369K }}
• {{cite journal |doi=10.1093/mnras/7.17.299 |doi-access=free |title=Discovery of Iris |journal=Monthly Notices of the Royal Astronomical Society |date=1847 |volume=7 |issue=17 |page=299 |bibcode=1847MNRAS...7..299.}}
• [https://web.archive.org/web/20140108202429/http://www.asteroidoccultation.com/observations/Results/Data2011/20110219_Iris%20Inversion%20Model.jpg 2011-Feb-19 Occultation] (Durech Model) / [https://web.archive.org/web/20140108170501/http://www.asteroidoccultation.com/observations/Results/index2011.html (2011 Asteroidal Occultation Results for North America)]
• [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=7 JPL Ephemeris]
• {{cite web |title=Elements and Ephemeris for (7) Iris |publisher=Minor Planet Center |url=http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00007 |url-status=dead |archive-url=https://web.archive.org/web/20160304112220/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00007 |archive-date=2016-03-04 }} (displays Elong from Sun and V mag for 2011)
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Category:Background asteroids

Iris

Iris

Category:S-type asteroids (Tholen)

Category:S-type asteroids (SMASS)

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