Editing 7 Iris

{{Short description|Large main-belt asteroid}}
{{About|the asteroid||Iris (disambiguation)}}
{{Use dmy dates|date=October 2019}}
{{Infobox planet
| minorplanet = yes
| background = #D6D6D6
| name = 7 Iris
| symbol = [[File:Iris symbol (fixed width).svg|32px]] (historical)
| image = Iris asteroid eso.jpg
| image_scale = 
| caption = Iris imaged by the [[Very Large Telescope]] in 2017<ref name="Hanus2019">{{cite journal
  |title=The shape of (7) Iris as evidence of an ancient large impact?
  |first1=J. |last1=Hanuš
  |first2=M. |last2=Marsset
  |first3=P. |last3=Vernazza
  |first4=M. |last4=Viikinkoski
  |first5=A. |last5=Drouard
  |first6=M. |last6=Brož
  |first7=B. |last7=Carry
  |first8=R. |last8=Fetick
  |display-authors=6
  |journal=Astronomy & Astrophysics
  |volume=624
  |number=A121
  |doi=10.1051/0004-6361/201834541
  |arxiv=1902.09242
  |bibcode=2018DPS....5040406H
  |date=24 April 2019|pages=A121 |s2cid=119089163 }}</ref>
| discoverer = [[John Russell Hind]]
| discovered = 13 August 1847
| mpc_name = (7) Iris
| pronounced = {{IPAc-en|ˈ|aɪ|r|ᵻ|s}}<ref>{{OED|iris}}</ref>
| adjectives = Iridian {{IPAc-en|ɪ|ˈ|r|ɪ|d|i|ə|n|,_|aɪ|-}}<ref>{{OED|iridian}}</ref>
| alt_names = 
| named_after = [[Iris (mythology)|Īris]]
| mp_category = [[Main belt]]
| orbit_ref = <ref name="jpldata"/>
| epoch = 13 September 2023<br/>([[Julian day|JD]]&nbsp;2453300.5)
| semimajor = {{Convert|2.387|AU|e6km|abbr=unit}}
| perihelion = {{Convert|1.838|AU|e6km|abbr=unit}}
| time_periastron = 4 April 2025
| aphelion = {{Convert|2.935|AU|e6km|abbr=unit|lk=on}}
| eccentricity = 0.22977
| period = 3.69 [[Julian year (astronomy)|a]] (1346.8 d)
| inclination = 5.519°
| asc_node = 259.5°
| arg_peri = 145.4°
| mean_anomaly = 207.9°
| moid = {{Convert|0.85|AU|e6km|abbr=unit}}<ref name="jpldata"/>
| avg_speed = 19.03 km/s
| p_orbit_ref = <ref name=Iris-POE>{{cite web
  |title=AstDyS-2 Iris Synthetic Proper Orbital Elements
  |publisher=Department of Mathematics, University of Pisa, Italy
  |url=https://newton.spacedys.com/astdys/index.php?pc=1.1.6&n=7
  |access-date=1 October 2011}}</ref>
| p_semimajor = 2.3862106
| p_eccentricity = 0.2125516
| p_inclination = 6.3924857°
| p_mean_motion = 97.653672
| perihelion_rate = 38.403324
| node_rate = −46.447128
| dimensions = {{val|268|x|234|x|180|u=km}}<br />±&nbsp;{{small|({{val|5|x|4|x|6|u=km}})}}<ref name="Hanus2019"/><br />{{val|225|x|190|x|190|u=km}}<ref name=Kaasalainen2002>{{cite journal| url=http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf| first= M.| last= Kaasalainen| title=Models of twenty asteroids from photometric data| journal= Icarus| volume= 159| issue=2| pages= 369–395| date=2002| doi=10.1006/icar.2002.6907| bibcode=2002Icar..159..369K|display-authors=etal}}</ref>
| mean_diameter = {{val|199|10|u=km}}<ref>{{Cite journal
 |last=Dudziński |first=G
 |display-authors=etal
 |date=14 October 2020
 |title=Volume uncertainty of (7) Iris shape models from disc-resolved images
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=499 |issue=3 |pages=4545–4560 |doi=10.1093/mnras/staa3153 |doi-access=free
 |issn=0035-8711
|hdl=10261/237568|hdl-access=free}}</ref><ref name="VLT">{{Cite journal
 |last=Vernazza |first=P.
 |display-authors=etal
 |date=October 2021
 |title=VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis
 |journal=[[Astronomy & Astrophysics]]
 |volume=654 |pages=A56
 |bibcode=2021A&A...654A..56V
 |doi=10.1051/0004-6361/202141781
 |issn=0004-6361
|hdl=10261/263281
 |hdl-access=free
 }}</ref><br />{{val|214|5|u=km}}<ref name="Hanus2019"/><br />{{val|199.83|10|u=km}} ([[IRAS]])<ref name="jpldata">{{cite web
  |type=2023-07-08 last obs.
  |title=JPL Small-Body Database Browser: 7 Iris
  |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=7
  |publisher=[[Jet Propulsion Laboratory]]
  |access-date=18 September 2023}}</ref>
| flattening = 0.42{{refn|1=Flattening derived from the maximum aspect ratio (c/a): <math>f=1-\frac{c}{a}</math>, where (c/a) = {{val|0.58|0.07}}.<ref name=VLT/>|group=lower-alpha}}
| surface_area = {{val|538460|u=km2}}{{refn|Calculated based on parameters calculated by J. Hanuš et al.<ref name="Hanus2019"/>|name=fact|group=lower-alpha}}
| volume = {{val|37153500|u=km3}}<ref group=lower-alpha name=fact/>
| mass = {{val|13.5|2.3|e=18|u=kg}}<ref name=VLT/>{{val|13.75|1.3|e=18|u=kg}}<ref name="Hanus2019"/>
| density = {{val|3.26|0.74|u=g/cm3}}<ref name=VLT/><br />{{val|2.7|0.3|u=g/cm3}}<ref name="Hanus2019"/>
| surface_grav = {{Gr|0.01375|107|3}} m/s²
| escape_velocity = {{V2|0.01375|107|3}} km/s
| rotation = {{convert|7.138843|h|d|abbr=on}}<ref name="Hanus2019"/>
| rot_velocity = 25.4 m/s<ref group=lower-alpha name=fact/>
| spectral_type = [[S-type asteroid|S]]
| magnitude = 6.7<ref name="Pasachoff1983">{{cite book
| author=Donald H. Menzel
| author2=Jay M. Pasachoff
| name-list-style=amp
| date=1983
| title=A Field Guide to the Stars and Planets
| edition=2nd
| publisher=Houghton Mifflin
| pages=[https://archive.org/details/fieldguidetostar00menz_0/page/391 391]
| location=Boston, MA
| isbn=0-395-34835-8
| url-access=registration
| url=https://archive.org/details/fieldguidetostar00menz_0/page/391
}}</ref><ref name=bright2006>{{cite web
  |title=Bright Minor Planets 2006
  |publisher=[[Minor Planet Center]]
  |url=http://www.cfa.harvard.edu/iau/Ephemerides/Bright/2006
  |access-date=2008-05-21
  }}{{Dead link|date=May 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
</ref> to 11.4
| abs_magnitude = 5.64<ref name="jpldata"/>
| albedo = 0.279<ref name=VLT/><br />{{val|0.2766|0.030}}<ref name="jpldata"/>
| angular_size = 0.32" <!-- Horizons 2006-Nov-15 --> to 0.07"
| single_temperature = ~171 [[kelvin|K]]<br />''max:''&nbsp;275&nbsp;K&nbsp;(+2°C)
}}

'''7 Iris''' is a large [[main-belt]] asteroid and possible remnant [[planetesimal]] orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the [[asteroid belt]]. 7 Iris is classified as an [[S-type asteroid]], meaning that it has a stony composition.

==Discovery and name==
Iris was discovered on 13 August 1847, by [[John Russell Hind|J. R. Hind]] from [[London]], [[United Kingdom|UK]]. It was Hind's first asteroid discovery and the seventh asteroid to be discovered overall. It was named after the [[rainbow]] goddess [[Iris (mythology)|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 (mythology)|Juno]] is the [[Roman mythology|Roman]] equivalent of Hera).

Iris's original symbol was a rainbow and a star: [[File:Iris symbol (fixed width).svg|16px]] or more simply [[File:Iris symbol (simple, fixed width).svg|16px]]. It is in the pipeline for [[Unicode]] 17.0 as U+1CEC1 𜻁 ([[File:Iris symbol (fixed width).svg|12px]]).<ref name=astunicode>{{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=}}</ref><ref name=pipeline>{{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=}}</ref>

==Characteristics==
[[Image:Moon and Asteroids 1 to 10.svg|thumb|left|Size comparison: the first 10 asteroids profiled against Earth's [[Moon]]. Iris is fourth from the right.]]

===Geology===
Iris is an S-type asteroid. The surface is bright and is probably a mixture of [[nickel]]-[[iron]] metals and [[magnesium]]- and iron-[[silicate]]s. Its spectrum is similar to that of [[L chondrite|L]] and [[LL chondrite]]s with corrections for [[space weathering]],<ref name="Ueda2003">{{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}}</ref> so it may be an important  contributor of these [[meteorites]]. Planetary dynamics also indicates that it should be a significant source of meteorites.<ref name="Migliorini">{{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}}
</ref>

Among the [[S-type asteroid]]s, Iris ranks fifth in [[mean diameter]] after [[15 Eunomia|Eunomia]], [[3 Juno|Juno]], [[29 Amphitrite|Amphitrite]] and [[532 Herculina|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.<ref name="Hanus2019"/>

===Brightness===
[[File:7Iris-LB1-richfield-mag10.jpg|thumb|left|Star rich field showing asteroid Iris ([[apparent magnitude|apmag]] 10.1)]]
Iris's bright surface and small distance from the Sun make it the fourth-brightest object in the [[asteroid belt]] after [[4 Vesta#Visibility|Vesta]], [[Ceres (dwarf planet)#Observations|Ceres]], and [[2 Pallas#Characteristics|Pallas]].  It has a ''[[mean]]'' opposition [[apparent magnitude|magnitude]] of +7.8, comparable to that of [[Neptune#Observation|Neptune]], and can easily be seen with [[binoculars]] at most oppositions. At typical [[opposition (astronomy)|opposition]]s it marginally outshines the larger though darker [[2 Pallas|Pallas]].<ref>{{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 }}</ref> 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),<ref name="Pasachoff1983" /> which is as bright as Ceres ever gets.

===Surface features===
A study by Hanus et al. using data from the [[Very Large Telescope|VLT]]'s SPHERE instrument names eight craters 20 to 40&nbsp;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.<ref name="Hanus2019"/>

{| class="wikitable"
|+ Named craters on Iris
|-
! width=100 | Feature !! Pronunciation !! Greek !! Meaning
|-
| Chloros || {{IPAc-en|ˈ|k|l|oʊ|r|ɒ|s}} || [[wikt:χλωρός|χλωρός]] || 'green'
|-
| Chrysos || {{IPAc-en|ˈ|k|r|aɪ|s|ɒ|s}} || [[wikt:χρῡσός|χρῡσός]] || 'gold'
|-
| Cirrhos || {{IPAc-en|ˈ|s|ɪr|ɒ|s}} || [[wikt:κιρρός|κιρρός]] || 'orange'{{refn|κιρρός is variously translated. The OED has 'orange-tawny'.<ref>{{OED|cirrhosis}}</ref> The color coding of the proposers in their crater maps, however, is simply orange.|name=|group=lower-alpha}}
|-
| Cyanos || {{IPAc-en|ˈ|s|aɪ|ə|n|ɒ|s}} || [[wikt:κύανος|κύανος]] || 'blue'
|-
| Erythros || {{IPAc-en|ˈ|ɛr|ɪ|θ|r|ɒ|s}} || [[wikt:ἐρυθρός|ἐρυθρός]] || 'red'
|-
| Glaucos || {{IPAc-en|ˈ|g|l|ɔː|k|ɒ|s}} || [[wikt:γλαυκός|γλαυκός]] || 'grey'{{refn|Or greyish blue-green.|name=|group=lower-alpha}}
|-
| Porphyra|| {{IPAc-en|ˈ|p|ɔr|f|ɪ|r|ə}} || [[wikt:πορφύρα|πορφύρα]] || 'purple'
|-
| Xanthos || {{IPAc-en|ˈ|z|æ|n|θ|ɒ|s}} || [[wikt:ξανθός|ξανθός]] || 'yellow'
|}

===Rotation===
Iris has a rotational period of 7.14 hours. Iris's north pole points towards the [[ecliptic coordinate system|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°,<ref>{{cite book|last=Pearson|first=Richard |title=The History of Astronomy|year=2020|isbn=9780244866501|page=349|publisher=Lulu.com }}</ref> 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.

==Observations==
[[Image:IrisOrbit.png|thumb|270px|The orbit of 7 Iris compared with the orbits of Earth, Mars and Jupiter]]
Iris was observed [[occultation|occulting]] a [[star]] on 26 May 1995, and later on 25 July 1997. Both observations gave a [[diameter]] of about 200&nbsp;km.

In February 2024, water molecules were discovered on 7 Iris, alongside [[20 Massalia]], marking the first time water molecules were detected on asteroids.<ref>{{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 H<sub>2</sub>O 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 }}</ref><ref>{{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}}</ref>

==See also==
* [[List of former planets]]

==Notes==
{{notelist|2|group=lower-alpha}}

==References==
{{reflist}}

==External links==
* {{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 [[Elongation (astronomy)|Elong]] from Sun and [[apparent magnitude|V mag]] for 2011)
* {{AstDys|7}}
* {{JPL small body}}

{{Minor planets navigator |6 Hebe |number=7 |8 Flora}}
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{{DEFAULTSORT:000007}}
[[Category:Background asteroids]]
[[Category:Discoveries by John Russell Hind|Iris]]
[[Category:Named minor planets|Iris]]
[[Category:S-type asteroids (Tholen)]]
[[Category:S-type asteroids (SMASS)]]
[[Category:Astronomical objects discovered in 1847|18470813]]