121 Hermione facts for kids
121 Hermione is a really big asteroid. It's a dark, carbon-rich space rock. Hermione travels in a special group called the Cybele group. This group is found far out in the main asteroid belt. Since it's a C-type asteroid, scientists think it's made of materials like carbon.
J. C. Watson found Hermione on May 12, 1872. It was named after Hermione from Greek mythology. She was the daughter of Menelaus and Helen.
Scientists have taken pictures of Hermione using special telescopes. These pictures show that the asteroid has an unusual shape. It looks a bit like a "snowman." This shape helps explain how Hermione's moon wobbles as it orbits.
By watching its moon, scientists could figure out Hermione's mass. They found that Hermione is not just a pile of loose rocks. It's more like a solid body, but with cracks inside. About 20% of its inside is empty space.
Hermione has passed in front of stars three times. The last time this happened was in February 2004. This event is called an Occultation.
Hermione's Moon: S/2002 (121) 1
A moon was found orbiting Hermione in 2002. It was discovered using the Keck II telescope. The moon's official name is S/2002 (121) 1.
Some astronomers have suggested naming it "LaFayette." This name would honor the ship used by the Marquis de Lafayette. He secretly sailed to America to help during the American Revolutionary War.
| Discovery | |
|---|---|
| Discovered by | W. J. Merline, P. M. Tamblyn, C. Dumas, L. M. Close, C. R. Chapman, F. Menard, W. M. Owen, and D. C. Slater |
| Discovery date | 28 September, 2002 |
| Designations | |
| Main belt (Cybele) | |
| Orbital characteristics | |
| 768 ± 11 km | |
| Eccentricity | 0.001 ± 0.001 |
| 2.582 ± 0.002 d | |
|
Average orbital speed
|
22 m/s |
| Inclination | 3 ± 2° with respect to Hermione pole |
| Satellite of | 121 Hermione |
| Physical characteristics | |
| Dimensions | 12 ± 4 km |
| Mass | ~1.6×1015 kg |
|
Equatorial escape velocity
|
~ 6 m/s |
| 13.0 | |
| Discovery | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Discovered by | James Craig Watson | ||||||||||||
| Discovery date | May 12, 1872 | ||||||||||||
| Designations | |||||||||||||
| 1970 VE | |||||||||||||
| Main belt (Cybele) | |||||||||||||
| Orbital characteristics | |||||||||||||
| Epoch December 31, 2006 (JD 2454100.5) | |||||||||||||
| Aphelion | 588.328 Gm (3.933 AU) | ||||||||||||
| Perihelion | 446.029 Gm (2.982 AU) | ||||||||||||
| 517.179 Gm (3.457 AU) | |||||||||||||
| Eccentricity | 0.138 | ||||||||||||
| 2347.854 d (6.43 a) | |||||||||||||
|
Average orbital speed
|
15.94 km/s | ||||||||||||
| 248.068° | |||||||||||||
| Inclination | 7.604° | ||||||||||||
| 73.209° | |||||||||||||
| 296.215° | |||||||||||||
| Known satellites | S/2002 (121) 1 | ||||||||||||
| Physical characteristics | |||||||||||||
| Dimensions | 254±4 × 125±9 km | ||||||||||||
|
Mean radius
|
95 km | ||||||||||||
| Mass | 5.4 ± 0.3×1018 kg | ||||||||||||
|
Mean density
|
1.8 ± 0.2 g/cm³ | ||||||||||||
|
Equatorial surface gravity
|
0.022 m/s² | ||||||||||||
|
Equatorial escape velocity
|
0.075 km/s | ||||||||||||
|
Sidereal rotation period
|
0.2313 d (5.551 h) | ||||||||||||
| 73° | |||||||||||||
|
Pole ecliptic latitude
|
+10 ± 2° | ||||||||||||
|
Pole ecliptic longitude
|
1.5 ± 2° | ||||||||||||
| 0.0482 ± 0.002 | |||||||||||||
|
|||||||||||||
| C | |||||||||||||
| 7.31 | |||||||||||||
- 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis. It has pictures and diagrams.
- Tally of Asteroids Harboring Moons Grows Beyond 30 (Space.com, October 3, 2002)
Images for kids
-
A 3D model of Hermione based on its lightcurve.
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See also
In Spanish: (121) Hermione para niños
