| Discovery[1] | |
|---|---|
| Discovered by | James Craig Watson |
| Discovery date | 12 May 1872 |
| Designations | |
| (121) Hermione | |
| Pronunciation | /hɜːrˈmaɪ.əniː/[2] |
Named after | Hermione[3] (Greek mythology) |
| A872 JA; 1970 VE | |
| main-belt · Cybele | |
| Adjectives | Hermionean/hɜːrmaɪ.əˈniːən/ |
| Orbital characteristics[4] | |
| Epoch 23 March 2018 (JD 2458200.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 145.96yr (53,312 d) |
| Aphelion | 3.9067AU |
| Perihelion | 2.9889 AU |
| 3.4478 AU | |
| Eccentricity | 0.1331 |
| 6.40 yr (2,338 d) | |
| 157.08° | |
| 0° 9m 14.4s / day | |
| Inclination | 7.5975° |
| 73.127° | |
| 298.18° | |
| Knownsatellites | S/2002 (121) 1 |
| Physical characteristics | |
| Dimensions | 268 × 186 × 183 km[5] (254 ± 4) × (125 ± 9) km[6] |
| 95 km[6] | |
| Volume | (3.0±0.4)×106 km3[7] |
| Mass | (5.381±5%)×1018 kg[7] |
Meandensity | 1.8 ± 0.2 g/cm3[7][a] |
Equatorialsurface gravity | 0.022 m/s2[b] |
Equatorialescape velocity | 0.075 km/s[b] |
| 0.2313 d (5.551 h)[8] | |
| 73° | |
| 1.5 ± 2° | |
| +10 ± 2°[7] | |
| 0.0482 ± 0.002[9] | |
| C[10] | |
| 7.31[9] | |
121 Hermione is a very large binaryasteroid discovered in 1872. It orbits in theCybele group in the far outerasteroid belt.[11] As an asteroid of the darkC spectral type, it is probably composed ofcarbonaceous materials. In 2002, a smallmoon was found to be orbiting Hermione.[11]
Hermione was discovered byJ. C. Watson on 12 May 1872 fromAnn Arbor, Michigan, in the United States,[11] and named afterHermione, daughter ofMenelaus andHelen inGreek mythology.[3]
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The asteroid has a bi-lobed shape, as evidenced byadaptive optics images, the first of which were taken in December 2003 with theKeck telescope.[6] Of several proposed shape models that agreed with the images, a "snowman"-like shape was found to best fit the observedprecession rate of Hermione's satellite.[7] In this "snowman" model, the asteroid's shape can be approximated by two partially overlapping spheres of radii 80 and 60 km, whose centers are separated by a distance of 115 km. A simpleellipsoid shape was ruled out.
Observation of the satellite's orbit has made possible an accurate determination of Hermione's mass.[7] For the best-fit "snowman" model, the density is found to be 1.8 ± 0.2 g/cm3, giving a porosity on the order of 20%, and possibly indicating that the main components are fractured solid bodies, rather than the asteroid being arubble pile.
Occultations by Hermione have been successfully observed three times so far, the last time in February 2004.
| Discovery[12] | |
|---|---|
| Discovered by | W. J. Merline, P. M. Tamblyn, C. Dumas, L. M. Close, C. R. Chapman, F. Menard, W. M. Owen, andD. C. Slater |
| Discovery date | 2002-09-28 |
| Designations | |
| LaFayette | |
| main-belt · Cybele | |
| Orbital characteristics[13] | |
| 768 ± 11 km | |
| Eccentricity | 0.001 ± 0.001 |
| 2.582 ± 0.002 d | |
| Inclination | 3 ± 2° (with respect to Hermione pole) |
| Satellite of | 121 Hermione |
| Physical characteristics | |
| Dimensions | 12 ± 4 km[6] |
| Mass | ~1.6×1015 kg[c] |
| 13.0[6] | |
Asatellite of Hermione was discovered in 2002 with theKeck II telescope.[11] It is about 8 miles (13 km) in diameter.[11] The satellite is provisionally designatedS/2002 (121) 1. It has not yet been officially named, but "LaFayette" has been proposed by a group of astronomers in reference tothe frigate used in secret by theMarquis de Lafayette to reach America to help the insurgents.[14][6]
