7 Iris

Template:Short description Template:About Template:Use dmy dates {{#invoke:infobox|infoboxTemplate | class = vcard | titleclass = fn org | title = 7 Iris | image = {{#invoke:InfoboxImage|InfoboxImage|image=Iris asteroid eso.jpg|upright={{#if:||1.1}}|alt=}} | caption = Iris imaged by the Very Large Telescope in 2017<ref name="Hanus2019">Template:Cite journal</ref> | headerstyle = {{#if:#D6D6D6|background-color:#D6D6D6|background-color:#E0CCFF}} | labelstyle = max-width:{{#if:||11em}}; | autoheaders = y

| header1 = Discovery

| header10 = {{#if:|Designations|Designations}}

| header20 = Orbital characteristics{{#ifeq:|yes| (barycentric)}}<ref name="jpldata"/>

| data21 = | data22 = {{#if:13 September 2023
(JD 2453300.5) |Epoch 13 September 2023
(JD 2453300.5)}} | data23 = {{#if: | Uncertainty parameter {{{uncertainty}}}}} | label24 = Observation arc | data24 = | label25 = Earliest precovery date | data25 = | label26 = {{#switch:{{{apsis}}} |apsis|gee|barion|center|centre|(apsis)=Apo{{{apsis}}} |Ap{{#if:|{{{apsis}}}|helion}}}} | data26 = Template:Convert | label27 = Peri{{#if:|{{{apsis}}}|helion}} | data27 = Template:Convert | label28 = Peri{{#if:|{{{apsis}}}|apsis}} | data28 = | label29 = {{#switch:{{{apsis}}} |helion|astron=Ap{{{apsis}}} |Apo{{#if:|{{{apsis}}}|apsis}}}} | data29 = | label30 = Periastron | data30 = | label31 = Apoastron | data31 = | label32 = Template:Longitem | data32 = Template:Convert | label33 = Template:Longitem | data33 = | label34 = Eccentricity | data34 = 0.22977 | label35 = Template:Longitem | data35 = 3.69 a (1346.8 d) | label36 = Template:Longitem | data36 = | label37 = Template:Longitem | data37 = 19.03 km/s | label38 = Template:Longitem | data38 = 207.9° | label39 = Template:Longitem | data39 = | label40 = Inclination | data40 = 5.519° | label41 = Template:Longitem | data41 = | label42 = Template:Longitem | data42 = 259.5° | label43 = Template:Longitem | data43 = | label44 = Template:Longitem | data44 = 4 April 2025 | label45 = Template:Longitem | data45 = 145.4° | label46 = Template:Nowrap | data46 = | label47 = Satellite of | data47 = | label48 = Group | data48 = | label49 = {{#switch: |yes|true=Satellites |Known satellites}} | data49 = | label50 = Star | data50 = | label51 = Earth MOID | data51 = Template:Convert<ref name="jpldata"/> | label52 = Mercury MOID | data52 = | label53 = Venus MOID | data53 = | label54 = Mars MOID | data54 = | label55 = Jupiter MOID | data55 = | label56 = Saturn MOID | data56 = | label57 = Uranus MOID | data57 = | label58 = Neptune MOID | data58 = | label59 = T_Jupiter | data59 =

| header60 = Proper orbital elements<ref name=Iris-POE>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

| label61 = Template:Longitem | data61 = {{#if:2.3862106 |2.3862106 AU}} | label62 = Template:Longitem | data62 = 0.2125516 | label63 = Template:Longitem | data63 = 6.3924857° | label64 = Template:Longitem | data64 = {{#if:97.653672 |97.653672 deg Template:\yr}} | label65 = Template:Longitem | data65 = {{#if:97.653672|{{#expr:360/97.653672 round 5}} yr
({{#expr:365.25*360/97.653672 round 3}} d) }} | label66 = Template:Longitem | data66 = {{#if:38.403324|38.403324 arcsec Template:\yr }} | label67 = Template:Longitem | data67 = {{#if:−46.447128|−46.447128 arcsec Template:\yr}}

| header70 = Template:Anchor{{#if:yes| Physical characteristics|Physical characteristics}}

| label71 = Dimensions | data71 = Template:Val
± Template:Small<ref name="Hanus2019"/>
Template:Val<ref name=Kaasalainen2002>Template:Cite journal</ref> | label72 = Template:Longitem | data72 = Template:Val<ref>Template:Cite journal</ref><ref name="VLT">Template:Cite journal</ref>
Template:Val<ref name="Hanus2019"/>
Template:Val (IRAS)<ref name="jpldata">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> | label73 = Template:Longitem | data73 = | label74 = Template:Longitem | data74 = | label75 = Template:Longitem | data75 = | label76 = Flattening | data76 = 0.42Template:Refn | label77 = Circumference | data77 = | label78 = Template:Longitem | data78 = Template:Val Template:Refn | label79 = Volume | data79 = Template:Val<ref group=lower-alpha name=fact/> | label80 = Mass | data80 = Template:Val<ref name=VLT/>Template:Val<ref name="Hanus2019"/> | label81 = Template:Longitem | data81 = Template:Val<ref name=VLT/>
Template:Val<ref name="Hanus2019"/> | label82 = Template:Longitem | data82 = Template:Gr m/s² | label83 = Template:Longitem | data83 = | label84 = Template:Longitem | data84 = Template:V2 km/s | label85 = Template:Longitem | data85 = Template:Convert<ref name="Hanus2019"/> | label86 = Template:Longitem | data86 = | label87 = Template:Longitem | data87 = 25.4 m/s<ref group=lower-alpha name=fact/> | label88 = Template:Longitem | data88 = | label89 = Template:Longitem | data89 = | label90 = Template:Longitem | data90 = | label91 = Template:Longitem | data91 = | label92 = Template:Longitem | data92 = | label93 = {{#if:yes |Template:Longitem |Albedo}} | data93 = 0.279<ref name=VLT/>
Template:Val<ref name="jpldata"/> | label94 = Temperature | data94 = ~171 K
max: 275 K (+2°C)

| data100 = {{#if:|

Surface temp.	min	mean	max
{{{temp_name1}}}
{{{temp_name2}}}
{{{temp_name3}}}
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| label101 = Surface absorbed dose rate | data101 = | label102 = Surface equivalent dose rate | data102 = | label103 = Template:Longitem | data103 = S | label104 = Template:Longitem | data104 = | label105 = Template:Longitem | data105 = 6.7<ref name="Pasachoff1983">Template:Cite book</ref><ref name=bright2006>{{#invoke:citation/CS1|citation |CitationClass=web }}Template:Dead link </ref> to 11.4 | label106 = Template:Longitem | data106 = 5.64<ref name="jpldata"/> | label107 = Template:Longitem | data107 = 0.32" to 0.07"

| header110 = Atmosphere

| below = {{#if:||Template:Reflist }}

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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 nameEdit

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: File:Iris symbol (fixed width).svg or more simply File:Iris symbol (simple, fixed width).svg. It is in the pipeline for Unicode 17.0 as U+1CEC1 𜻁 (File:Iris symbol (fixed width).svg).<ref name=astunicode>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=pipeline>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

CharacteristicsEdit

File:Moon and Asteroids 1 to 10.svg

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

GeologyEdit

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,<ref name="Ueda2003">Template:Cite conference</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">Template:Cite journal </ref>

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.<ref name="Hanus2019"/>

BrightnessEdit

File:7Iris-LB1-richfield-mag10.jpg

Star rich field showing asteroid Iris (apmag 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</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 featuresEdit

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.<ref name="Hanus2019"/>

Named craters on Iris
Feature	Pronunciation	Greek	Meaning
Chloros	Template:IPAc-en	χλωρός	'green'
Chrysos	Template:IPAc-en	χρῡσός	'gold'
Cirrhos	Template:IPAc-en	κιρρός	'orange'Template:Refn
Cyanos	Template:IPAc-en	κύανος	'blue'
Erythros	Template:IPAc-en	ἐρυθρός	'red'
Glaucos	Template:IPAc-en	γλαυκός	'grey'Template:Refn
Porphyra	Template:IPAc-en	πορφύρα	'purple'
Xanthos	Template:IPAc-en	ξανθός	'yellow'

RotationEdit

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°,<ref>Template:Cite book</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.

ObservationsEdit

File:IrisOrbit.png

The orbit of 7 Iris compared with the orbits of Earth, Mars and Jupiter

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.<ref>Template:Cite journal</ref><ref>Template:Cite news</ref>