Minorplanet: | yes |
121 Hermione | |
Background: |
|
Discovered: | 12 May 1872 |
Mpc Name: | (121) Hermione |
Alt Names: | A872 JA; 1970 VE |
Pronounced: | [1] |
Adjective: | Hermionean |
Named After: | Hermione |
Epoch: | 23 March 2018 (JD 2458200.5) |
Uncertainty: | 0 |
Observation Arc: | 145.96 yr (53,312 d) |
Perihelion: | 2.9889 AU |
Semimajor: | 3.4478 AU |
Eccentricity: | 0.1331 |
Period: | 6.40 yr (2,338 d) |
Mean Motion: | / day |
Inclination: | 7.5975° |
Asc Node: | 73.127° |
Arg Peri: | 298.18° |
Satellites: | S/2002 (121) 1 |
Dimensions: | 268 × 186 × 183 km[2] (254 ± 4) × (125 ± 9) km[3] |
Mean Radius: | 95 km |
Mass: | [4] |
Density: | 1.8 ± 0.2 g/cm3 |
Surface Grav: | 0.022 m/s2 |
Escape Velocity: | 0.075 km/s |
Sidereal Day: | 0.2313 d (5.551 h)[5] |
Axial Tilt: | 73° |
Pole Ecliptic Lat: | +10 ± 2° |
Pole Ecliptic Lon: | 1.5 ± 2° |
Albedo: | 0.0482 ± 0.002[6] |
Spectral Type: | C[7] |
Abs Magnitude: | 7.31 |
121 Hermione is a very large binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt. As an asteroid of the dark C spectral type, it is probably composed of carbonaceous materials. In 2002, a small moon was found to be orbiting Hermione.[8]
Hermione was discovered by J. C. Watson on 12 May 1872 from Ann Arbor, Michigan, in the United States,[8] and named after Hermione, daughter of Menelaus and Helen in Greek mythology.
thumb|left|Lightcurve-based 3D-model of HermioneThe asteroid has a bi-lobed shape, as evidenced by adaptive optics images, the first of which were taken in December 2003 with the Keck telescope.[3] Of several proposed shape models that agreed with the images, a "snowman"-like shape was found to best fit the observed precession rate of Hermione's satellite.[4] 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 simple ellipsoid shape was ruled out.
Observation of the satellite's orbit has made possible an accurate determination of Hermione's mass.[4] 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 a rubble pile.
Occultations by Hermione have been successfully observed three times so far, the last time in February 2004.
S/2002 (121) 1 | |
Bgcolour: |
|
Minorplanet: | yes |
Discovery Ref: | [9] |
Discoverer: | W. J. Merline, P. M. Tamblyn, C. Dumas, L. M. Close, C. R. Chapman, F. Menard, W. M. Owen, and D. C. Slater |
Discovered: | 2002-09-28 |
Alt Names: | LaFayette |
Mp Category: | main-beltCybele |
Orbit Ref: | [10] |
Semimajor: | 768 ± 11 km |
Eccentricity: | 0.001 ± 0.001 |
Period: | 2.582 ± 0.002 d |
Satellite Of: | 121 Hermione |
Inclination: | 3 ± 2° |
Dimensions: | 12 ± 4 km |
Mass: | ~1.6 kg |
Abs Magnitude: | 13.0 |
A satellite of Hermione was discovered in 2002 with the Keck II telescope.[8] It is about 8 miles (13 km) in diameter.[8] The satellite is provisionally designated S/2002 (121) 1. It has not yet been officially named, but "LaFayette" has been proposed by a group of astronomers in reference to the frigate used in secret by the Marquis de Lafayette to reach America to help the insurgents.[3]