7 Iris

Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0
name=7 Iris
symbol=
discoverer=John Russell Hind
discovered=August 13, 1847
alt_names="none"
adjectives=Iridian
mp_category=Main belt


epoch=November 26, 2005 (JD 2453700.5)
semimajor=356.798 Gm (2.385 AU)
perihelion=274.259 Gm (1.833 AU)
aphelion=439.337 Gm (2.937 AU)
eccentricity=0.231
period=1345.375 d (3.68 a)
inclination=5.527°
asc_node=259.727°
arg_peri=145.440°
mean_anomaly=269.531°
avg_speed=19.03 km/s
dimensions=225×190×190 kmcite web| url=http://www.psi.edu/pds/archive/astdata04/simps04/diamalb.tab| title= Supplemental IRAS Minor Planet Survey] cite journal| url=http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf| first= M.| last= Kaasalainen| coauthors= et al| title=Models of twenty asteroids from photometric data| journal= Icarus| volume= 159| pages= 369| year=2002| doi=10.1006/icar.2002.6907]
mass=1.25×10¹⁹ kgcite journal | last= Pitjeva | first=E. V. | authorlink= Elena V. Pitjeva | title= High-Precision Ephemerides of Planets—EPM and Determination of Some Astronomical Constants | journal= Solar System Research | year= 2005 | volume= 39 | issue= 3 | pages= 176 | url= http://iau-comm4.jpl.nasa.gov/EPM2004.pdf | format= PDF | doi= 10.1007/s11208-005-0033-2]
density=2.9 g/cm³
surface_grav=0.055 m/s²
escape_velocity=0.11 km/s
rotation=0.2975 d [cite web| url=http://www.psi.edu/pds/archive/lc.html| title= Planetary Data System Small Bodies Node, lightcurve parameters]
spectral_type=S-type asteroid
magnitude = 6.7cite book
author=Donald H. Menzel and Jay M. Pasachoff
year=1983
title=A Field Guide to the Stars and Planets
edition=2nd edition
publisher=Houghton Mifflin
pages=p. 391
location=Boston, MA
id=ISBN 0395348358 ] cite web
title=Bright Minor Planets 2006
publisher=Minor Planet Center
url=http://www.cfa.harvard.edu/iau/Ephemerides/Bright/2006
accessdate=2008-05-21] to 11.4
abs_magnitude=5.51
albedo=0.277 (geometric)
angular_size = 0.32" to 0.07"
single_temperature=~171 K
"max:" 275 K (+2° C)

7 Iris (pronEng|ˈaɪrɪs, _gr. "Ίρις)" is a large main belt asteroid. Among S-type asteroids it ranks fifth in geometric mean diameter after Eunomia, Juno, Amphitrite and Herculina.

Its bright surface and small distance from the Sun make Iris the fourth brightest object in the asteroid belt after Vesta, Ceres, and Pallas. But 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 | accessdate=2007-07-16 ] . 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 rare oppositions near perihelion Iris can reach a magnitude of +6.7, which is as bright as Ceres ever gets, and reports of it being seen without optical aid are unverified.

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. 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 in the northern hemisphere.cite journal| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993A%26AS..101..621H&db_key=AST&data_type=HTML&format=&high=43957df91429645| first=M.| last= Hoffmann| coauthors= E. H. Geyer| title=Spots on 4-VESTA and 7-IRIS - Large Areas or Little Patches| journal= Astronomy & Astrophysics Supplement| volume= 101| pages= 621| year=1993]

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, [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003LPI....34.2078U&db_key=AST&data_type=HTML&format=&high=43957df91430901 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).] 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| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...321..652M&db_key=AST&data_type=HTML&format=&high=43957df91431538| first= F.| last= Migliorini| coauthors= et al| title=(7) Iris: a possible source of ordinary chondrites?| journal=Astronomy & Astrophysics| volume= 321| pages=652| year=1997]

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.

References

External links

* [http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf shape model deduced from lightcurve]
* [http://adsabs.harvard.edu//full/seri/MNRAS/0007//0000299.000.html "Discovery of Iris", MNRAS 7 (1847) 299]
* — Horizons can be used to obtain a current ephemeris.