7 Iris

Last updated

7 Iris
Iris asteroid eso.jpg
Iris imaged by the Very Large Telescope in 2017 [1]
Discovery
Discovered by John Russell Hind
Discovery date13 August 1847
Designations
(7) Iris
Pronunciation /ˈaɪrɪs/ [2]
Named after
 Īris
Main belt
Adjectives Iridian /ɪˈrɪdiən,aɪ-/ [3]
Symbol Iris symbol (fixed width).svg (historical)
Orbital characteristics [4]
Epoch 13 September 2023
(JD  2453300.5)
Aphelion 2.935  AU (439.1 million  km)
Perihelion 1.838 AU (275.0 million km)
2.387 AU (357.1 million km)
Eccentricity 0.22977
3.69 a (1346.8 d)
Average orbital speed
19.03 km/s
207.9°
Inclination 5.519°
259.5°
4 April 2025
145.4°
Earth  MOID 0.85 AU (127 million km) [4]
Proper orbital elements [5]
2.3862106  AU
Proper eccentricity
0.2125516
Proper inclination
6.3924857°
Proper mean motion
97.653672  deg  / yr
3.6865 yr
(1346.493 d)
Precession of perihelion
38.403324  arcsec  / yr
Precession of the ascending node
−46.447128  arcsec  / yr
Physical characteristics
Dimensions 268 km × 234 km × 180 km
± (5 km × 4 km × 6 km) [1]
225 km × 190 km × 190 km [6]
199±10 km [7] [8]
214±5 km [1]
199.83±10 km (IRAS) [4]
Flattening 0.42 [lower-alpha 1]
538460 km2 [lower-alpha 2]
Volume 37153500 km3 [lower-alpha 2]
Mass (13.5±2.3)×1018 kg [8] (13.75±1.3)×1018 kg [1]
Mean density
3.26±0.74 g/cm3 [8]
2.7±0.3 g/cm3 [1]
Equatorial surface gravity
0.08 m/s²
Equatorial escape velocity
0.131 km/s
7.138843 h (0.2974518 d) [1]
Equatorial rotation velocity
25.4 m/s [lower-alpha 2]
0.279 [8]
0.2766±0.030 [4]
Temperature ~171 K
max: 275 K (+2°C)
S
6.7 [9] [10] to 11.4
5.64 [4]
0.32" to 0.07"

    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.

    Contents

    Discovery and name

    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: Iris symbol (fixed width).svg or more simply Iris symbol (simple, fixed width).svg . It is in the pipeline for Unicode 17.0 as U+1CEC1 𜻁 ( Iris symbol (fixed width).svg ). [11] [12]

    Characteristics

    Size comparison: the first 10 asteroids profiled against Earth's Moon. Iris is fourth from the right. Moon and Asteroids 1 to 10.svg
    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-silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering, [13] so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites. [14]

    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. [1]

    Brightness

    Star rich field showing asteroid Iris (apmag 10.1) 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. [15] 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), [9] which is as bright as Ceres ever gets.

    Surface features

    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. [1]

    Named craters on Iris
    FeaturePronunciationGreekMeaning
    Chloros /ˈkloʊrɒs/ χλωρός 'green'
    Chrysos /ˈkraɪsɒs/ χρῡσός 'gold'
    Cirrhos /ˈsɪrɒs/ κιρρός 'orange' [lower-alpha 3]
    Cyanos /ˈsaɪənɒs/ κύανος 'blue'
    Erythros /ˈɛrɪθrɒs/ ἐρυθρός 'red'
    Glaucos /ˈɡlɔːkɒs/ γλαυκός 'grey' [lower-alpha 4]
    Porphyra /ˈpɔːrfɪrə/ πορφύρα 'purple'
    Xanthos /ˈzænθɒs/ ξανθός 'yellow'

    Rotation

    Iris has a rotational period of 7.14 hours. Iris’ 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°, [17] 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

    The orbit of 7 Iris compared with the orbits of Earth, Mars and Jupiter 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. [18] [19]

    See also

    Notes

    1. ↑ Flattening derived from the maximum aspect ratio (c/a): , where (c/a) = 0.58±0.07. [8]
    2. 1 2 3 Calculated based on parameters calculated by J. Hanuš et al. [1]
    3. ↑ κιρρός is variously translated. The OED has 'orange-tawny'. [16] The color coding of the proposers in their crater maps, however, is simply orange.
    4. ↑ Or greyish blue-green.

    Related Research Articles

    <span class="mw-page-title-main">16 Psyche</span> Metallic main-belt asteroid

    16 Psyche is a large M-type asteroid, which was discovered by the Italian astronomer Annibale de Gasparis, on 17 March 1852 and named after the Greek goddess Psyche. The prefix "16" signifies that it was the sixteenth minor planet in order of discovery. It is the largest and most massive of the M-type asteroids, and one of the dozen most massive asteroids. It has a mean diameter of approximately 220 kilometers (140 mi) and contains about one percent of the cumulative mass of the whole asteroid belt. It was thought to be the exposed core of a protoplanet, but recent observations cast doubt on that hypothesis. Psyche will be explored by NASA, with a spacecraft of the same name, marking the first time a manmade object will journey to a metallic asteroid, launched on 13 October 2023, with an expected arrival in 2029.

    <span class="mw-page-title-main">5 Astraea</span> Large asteroid

    5 Astraea is an asteroid in the asteroid belt. This object is orbiting the Sun at a distance of 385 million kilometres (2.5735 AU) with a period of 4.13 yr and an orbital eccentricity of 0.19. The orbital plane is inclined at an angle of 5.37° to the plane of the ecliptic. It is spinning with a period of 16.8 h. The surface of Astraea is highly reflective and its composition is probably a mixture of nickel–iron with silicates of magnesium and iron. It is an S-type asteroid in the Tholen classification system.

    <span class="mw-page-title-main">8 Flora</span> Large main-belt asteroid

    8 Flora is a large, bright main-belt asteroid. It is the innermost large asteroid: no asteroid closer to the Sun has a diameter above 25 kilometres, and not until 20-km 149 Medusa was discovered was an asteroid known to orbit at a closer mean distance. It is the seventh-brightest asteroid with a mean opposition magnitude of +8.7. Flora can reach a magnitude of +8.1 at a favorable opposition near perihelion, such as occurred in November 2020 when it was 0.88 AU from Earth.

    <span class="mw-page-title-main">10 Hygiea</span> Major asteroid

    10 Hygiea is a major asteroid located in the main asteroid belt. With a mean diameter of between 425 and 440 km and a mass estimated to be 3% of the total mass of the belt, it is the fourth-largest asteroid in the Solar System by both volume and mass, and is the largest of the C-type asteroids in classifications that use G type for 1 Ceres. It is very close to spherical, apparently because it had re-accreted after the disruptive impact that produced the large Hygiean family of asteroids.

    <span class="mw-page-title-main">11 Parthenope</span> Main-belt asteroid

    11 Parthenope is a large, bright main-belt asteroid.

    <span class="mw-page-title-main">15 Eunomia</span> Main-belt asteroid

    15 Eunomia is a very large asteroid in the middle asteroid belt. It is the largest of the stony (S-type) asteroids, with 3 Juno as a close second. It is quite a massive asteroid, in 6th to 8th place. It is the largest Eunomian asteroid, and is estimated to contain 1% of the mass of the asteroid belt.

    <span class="mw-page-title-main">29 Amphitrite</span> Main-belt asteroid

    29 Amphitrite is one of the largest S-type asteroids, approximately 200 kilometers in diameter, and probably fifth largest after Eunomia, Juno, Iris and Herculina.

    <span class="mw-page-title-main">32 Pomona</span> Main-belt asteroid

    32 Pomona is a stony main-belt asteroid that is 81 kilometres (50 mi) in diameter. It was discovered by German-French astronomer Hermann Mayer Salomon Goldschmidt on October 26, 1854, and is named after Pōmōna, the Roman goddess of fruit trees.

    <span class="mw-page-title-main">43 Ariadne</span> Main-belt asteroid

    43 Ariadne is a fairly large and bright main-belt asteroid. It is the second-largest member of the Flora asteroid family. It was discovered by N. R. Pogson on 15 April 1857 and named after the Greek heroine Ariadne.

    <span class="mw-page-title-main">44 Nysa</span> Main-belt asteroid

    44 Nysa is a large and very bright main-belt asteroid, and the brightest member of the Nysian asteroid family. It is classified as a rare class E asteroid and is probably the largest of this type.

    <span class="mw-page-title-main">94 Aurora</span> Main-belt asteroid

    94 Aurora is one of the largest main-belt asteroids. With an albedo of only 0.04, it is darker than soot, and has a primitive composition consisting of carbonaceous material. It was discovered by J. C. Watson on September 6, 1867, in Ann Arbor, and named after Aurora, the Roman goddess of the dawn.

    <span class="mw-page-title-main">125 Liberatrix</span> Main-belt asteroid

    125 Liberatrix is a main-belt asteroid. It has a relatively reflective surface and an M-type spectrum. Liberatrix is a member of an asteroid family bearing its own name.

    <span class="mw-page-title-main">130 Elektra</span> Asteroid with 3 moons

    130 Elektra is a large outer main-belt asteroid and quadruple system with three minor-planet moons. It was discovered on 17 February 1873, by astronomer Christian Peters at Litchfield Observatory, New York, and named after Electra, an avenger in Greek mythology.

    <span class="mw-page-title-main">704 Interamnia</span> Large asteroid in the asteroid belt

    704 Interamnia is a large F-type asteroid. With a mean diameter of around 330 kilometres, it is the fifth-largest asteroid, after Ceres, Vesta, Pallas and Hygiea. Its mean distance from the Sun is 3.067 AU. It was discovered on 2 October 1910 by Vincenzo Cerulli, and named after the Latin name for Teramo, Italy, where Cerulli worked. Its mass is probably between fifth and tenth highest in the asteroid belt, with a mass estimated to be 1.2% of the mass of the entire asteroid belt. Observations by the Very Large Telescope's SPHERE imager in 2017–2019, combined with occultation results, indicate that the shape of Interamnia may be consistent with hydrostatic equilibrium for a body of its density with a rotational period of 7.6 hours. This suggests that Interamnia may have formed as an equilibrium body, and that impacts changed its rotational period after it fully solidified.

    <span class="mw-page-title-main">354 Eleonora</span> Main-belt asteroid

    354 Eleonora is a large, stony main-belt asteroid that was discovered by the French astronomer Auguste Charlois on January 17, 1893, in Nice.

    412 Elisabetha is a large main belt asteroid that was discovered by German astronomer Max Wolf on 7 January 1896 in Heidelberg. It may have been named after his mother, Elise Wolf. This minor planet is orbiting at a distance of 2.76 AU from the Sun with a period of 4.59 years and an orbital eccentricity (ovalness) of 0.044. The orbital plane is inclined at an angle of 13.8° to the plane of the ecliptic.

    <span class="mw-page-title-main">423 Diotima</span> Main-belt asteroid

    423 Diotima is one of the larger main-belt asteroids. It is classified as a C-type asteroid and is probably composed of primitive carbonaceous material.

    <span class="mw-page-title-main">776 Berbericia</span>

    776 Berbericia is a minor planet orbiting the Sun. A main-belt C-type asteroid, it was discovered on 24 January 1914 by astronomer Adam Massinger at Heidelberg Observatory in southwest Germany. It was named by Max Wolf in honor of Adolf Berberich (1861–1920), a German astronomer. The spectra of the asteroid displays evidence of aqueous alteration.

    <span class="mw-page-title-main">849 Ara</span>

    849 Ara is a large, metallic background asteroid, approximately 80 kilometers in diameter, that is located in the outer region of the asteroid belt. It was discovered on 9 February 1912, by Russian astronomer Sergey Belyavsky at the Simeiz Observatory on the Crimean peninsula. The M-type asteroid has a short rotation period of 4.1 hours and is likely elongated in shape. It was named after the American Relief Administration (ARA) for the help given during the Russian famine of 1921–22.

    References

    1. 1 2 3 4 5 6 7 8 9 Hanuš, J.; Marsset, M.; Vernazza, P.; Viikinkoski, M.; Drouard, A.; Brož, M.; et al. (24 April 2019). "The shape of (7) Iris as evidence of an ancient large impact?". Astronomy & Astrophysics. 624 (A121): A121. arXiv: 1902.09242 . Bibcode:2018DPS....5040406H. doi:10.1051/0004-6361/201834541. S2CID   119089163.
    2. ↑ "iris" . Oxford English Dictionary (Online ed.). Oxford University Press.(Subscription or participating institution membership required.)
    3. ↑ "iridian" . Oxford English Dictionary (Online ed.). Oxford University Press.(Subscription or participating institution membership required.)
    4. 1 2 3 4 5 "JPL Small-Body Database Browser: 7 Iris" (2023-07-08 last obs.). Jet Propulsion Laboratory . Retrieved 18 September 2023.
    5. ↑ "AstDyS-2 Iris Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Retrieved 1 October 2011.
    6. ↑ Kaasalainen, M.; et al. (2002). "Models of twenty asteroids from photometric data" (PDF). Icarus. 159 (2): 369–395. Bibcode:2002Icar..159..369K. doi:10.1006/icar.2002.6907.
    7. ↑ Dudziński, G; et al. (14 October 2020). "Volume uncertainty of (7) Iris shape models from disc-resolved images". Monthly Notices of the Royal Astronomical Society . 499 (3): 4545–4560. doi: 10.1093/mnras/staa3153 . hdl: 10261/237568 . ISSN   0035-8711.
    8. 1 2 3 4 5 Vernazza, P.; et al. (October 2021). "VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis". Astronomy & Astrophysics . 654: A56. Bibcode:2021A&A...654A..56V. doi:10.1051/0004-6361/202141781. hdl: 10261/263281 . ISSN   0004-6361.
    9. 1 2 Donald H. Menzel & Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd ed.). Boston, MA: Houghton Mifflin. pp.  391. ISBN   0-395-34835-8.
    10. ↑ "Bright Minor Planets 2006". Minor Planet Center . Retrieved 21 May 2008.[ permanent dead link ]
    11. ↑ Bala, Gavin Jared; Miller, Kirk (18 September 2023). "Unicode request for historical asteroid symbols" (PDF). unicode.org. Unicode. Retrieved 26 September 2023.
    12. ↑ Unicode. "Proposed New Characters: The Pipeline". unicode.org. The Unicode Consortium. Retrieved 6 November 2023.
    13. ↑ Ueda, Y.; Miyamoto, M.; Mikouchi, T.; Hiroi, T. (March 2003). Surface Material Analysis of the S-type Asteroids: Removing the Space Weathering Effect from Reflectance Spectrum. 34th Annual Lunar and Planetary Science Conference. p. 2078. Bibcode:2003LPI....34.2078U.
    14. ↑ Migliorini, F.; et al. (1997). "(7) Iris: a possible source of ordinary chondrites?". Astronomy & Astrophysics. 321: 652. Bibcode:1997A&A...321..652M.
    15. ↑ Odeh, Moh'd. "The Brightest Asteroids". Jordanian Astronomical Society. Archived from the original on 13 August 2007. Retrieved 16 July 2007.
    16. ↑ "cirrhosis" . Oxford English Dictionary (Online ed.). Oxford University Press.(Subscription or participating institution membership required.)
    17. ↑ Pearson, Richard (2020). The History of Astronomy. Lulu.com. p. 349. ISBN   9780244866501.
    18. ↑ Arredondo, Anicia; McAdam, Margaret M.; Honniball, Casey I.; Becker, Tracy M.; Emery, Joshua P.; Rivkin, Andrew S.; Takir, Driss; Thomas, Cristina A. (12 February 2024). "Detection of Molecular H2O on Nominally Anhydrous Asteroids". The Planetary Science Journal. 5 (2): 37. Bibcode:2024PSJ.....5...37A. doi: 10.3847/PSJ/ad18b8 .
    19. ↑ Gamillo, Elizabeth (14 February 2024). "Water molecules identified on asteroids for the first time". Astronomy. Retrieved 27 March 2024.
    This page is based on this Wikipedia article
    Text is available under the CC BY-SA 4.0 license; additional terms may apply.
    Images, videos and audio are available under their respective licenses.