7 Iris
Star rich field showing asteroid Iris (apmag 10.1)
|
|
| Discovery | |
|---|---|
| Discovered by | John Russell Hind |
| Discovery date | August 13, 1847 |
| Designations | |
| Pronunciation | /ˈaɪərᵻs/ YR-is |
|
Named after
|
Īris |
| none | |
| Main belt | |
| Adjectives | Iridian /aɪˈrɪdiən/ |
| Orbital characteristics | |
| Epoch November 26, 2005 (JD 2453700.5) | |
| Aphelion | 2.937 AU (439.337 Gm) |
| Perihelion | 1.833 AU (274.259 Gm) |
| 2.385 AU (356.798 Gm) | |
| Eccentricity | 0.231 |
| 3.68 a (1345.375 d) | |
|
Average orbital speed
|
19.03 km/s |
| 269.531° | |
| Inclination | 5.527° |
| 259.727° | |
| 145.440° | |
| Proper orbital elements | |
|
Proper semi-major axis
|
2.3862106 AU |
|
Proper eccentricity
|
0.2125516 |
|
Proper inclination
|
6.3924857° |
|
Proper mean motion
|
97.653672 deg / yr |
|
Proper orbital period
|
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 | 240×200×200 km 225×190×190 km 199.8 ± 10 km (IRAS) |
| 135 000 km2 | |
| Volume | 4 630 000 km3 |
| Mass | 1.62 ± 0.09 ×1019 kg |
|
Mean density
|
3.21 ± 0.49 g/cm³ |
| 0.108 m/s² | |
| 0.147 km/s | |
| 0.2975 d | |
|
Equatorial rotation velocity
|
25.4 m/s |
| Albedo | 0.277 (geometric) |
| Temperature | ~171 K max: 275 K (+2°C) |
|
Spectral type
|
S-type asteroid |
| 6.7 to 11.4 | |
| 5.51 | |
| 0.32" to 0.07" | |
7 Iris is a large main-belt asteroid orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. It is classified as an S-type asteroid, meaning that it has a stony composition.
Iris was discovered on August 13, 1847, by J. R. Hind from London, UK. It was Hind's first asteroid discovery and the seventh asteroid to be discovered overall.
Iris 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 she was spotted following 3 Juno by less than an hour of right ascension (Juno is the Roman equivalent of Hera).
Iris regularly comes within 0.4AU of Mars and will next do so on November 2, 2054.
Iris is an S-type asteroid. Its surface likely exhibits albedo differences, with possibly a large bright area in the northern hemisphere. Overall the surface is 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, so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.
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Wikipedia