Astronomy:121 Hermione
 121 Hermione and its moon | |
| Discovery[1] | |
|---|---|
| Discovered by | James Craig Watson |
| Discovery date | 12 May 1872 |
| Designations | |
| (121) Hermione | |
| Pronunciation | /hɜːrˈmaɪ.əniː/[3] |
| Named after | Hermione[2] (Greek mythology) |
| A872 JA; 1970 VE | |
| Minor planet category | main-belt · Cybele |
| Adjectives | Hermionean /hɜːrmaɪ.əˈniːən/ |
| Orbital characteristics[4] | |
| Epoch 23 March 2018 (JD 2458200.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 145.96 yr (53,312 d) |
| |{{{apsis}}}|helion}} | 3.9067 AU |
| |{{{apsis}}}|helion}} | 2.9889 AU |
| 3.4478 AU | |
| Eccentricity | 0.1331 |
| Orbital period | 6.40 yr (2,338 d) |
| Mean anomaly | 157.08° |
| Mean motion | 0° 9m 14.4s / day |
| Inclination | 7.5975° |
| Longitude of ascending node | 73.127° |
| 298.18° | |
| Known satellites | S/2002 (121) 1 |
| Physical characteristics | |
| Mean radius | 95 km[5] |
| Volume | (3.0±0.4)×106 km3[6] |
| Mass | (5.381±5%)×1018 kg[6] |
| Mean density | 1.8 ± 0.2 g/cm3[6][lower-alpha 1] |
Equatorial surface gravity | 0.022 m/s2[lower-alpha 2] |
Equatorial escape velocity | 0.075 km/s[lower-alpha 2] |
| Sidereal rotation period | 0.2313 d (5.551 h)[7] |
| Axial tilt | 73° |
| Pole ecliptic latitude | +10 ± 2°[6] |
| Pole ecliptic longitude | 1.5 ± 2° |
| Geometric albedo | 0.0482 ± 0.002[8] |
| C[9] | |
| Absolute magnitude (H) | 7.31[8] |
121 Hermione is a very large binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt.[10] 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.[10]
Discovery
Hermione was discovered by J. C. Watson on 12 May 1872 from Ann Arbor, Michigan, in the United States,[10] and named after Hermione, daughter of Menelaus and Helen in Greek mythology.[2]
Physical properties
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The 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.[5] 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.[6] 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.[6] 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.
| Discovery[11] | |
|---|---|
| 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 | 2002-09-28 |
| Designations | |
| LaFayette | |
| Minor planet category | main-belt · Cybele |
| Orbital characteristics[12] | |
| 768 ± 11 km | |
| Eccentricity | 0.001 ± 0.001 |
| Orbital period | 2.582 ± 0.002 d |
| Inclination | 3 ± 2° (with respect to Hermione pole) |
| Satellite of | 121 Hermione |
| Physical characteristics | |
| Dimensions | 12 ± 4 km[5] |
| Mass | ~1.6×1015 kg[lower-alpha 3] |
| Absolute magnitude (H) | 13.0[5] |
Moon
A satellite of Hermione was discovered in 2002 with the Keck II telescope.[10] It is about 8 miles (13 km) in diameter.[10] 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.[13][5]
Notes
References
- ↑ "121 Hermione". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=121. Retrieved 14 September 2018.
- ↑ 2.0 2.1 Schmadel, Lutz D. (2007). "(121) Hermione". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 26. doi:10.1007/978-3-540-29925-7_122. ISBN 978-3-540-00238-3.
- ↑ Noah Webster (1884) A Practical Dictionary of the English Language
- ↑ "JPL Small-Body Database Browser: 121 Hermione". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000121. Retrieved 14 September 2018.
- ↑ 5.0 5.1 5.2 5.3 5.4 Cite error: Invalid
<ref>tag; no text was provided for refs namedMarKaaHom06 - ↑ 6.0 6.1 6.2 6.3 6.4 6.5 F. Marchis (2005). "Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit". Icarus 178 (2): 450–464. doi:10.1016/j.icarus.2005.05.003. Bibcode: 2005Icar..178..450M.
- ↑ IAUC 8264
- ↑ 8.0 8.1 Supplemental IRAS minor planet survey
- ↑ PDS node taxonomy database
- ↑ 10.0 10.1 10.2 10.3 10.4 Linda T. Elkins-Tanton (2010). Asteroids, Meteorites, and Comets. Infobase Publishing. p. 96. ISBN 978-1-4381-3186-3. https://books.google.com/books?id=K-0xBsMsursC&pg=PA96.
- ↑ IAUC 7980
- ↑ 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis.
- ↑ Johnston, Wm. Robert (21 September 2014). "(121) Hermione and S/2002 (121) 1 ("LaFayette")". Asteroids with Satellites Database. Johnston's Archive. http://www.johnstonsarchive.net/astro/astmoons/am-00121.html. Retrieved 7 November 2021.
External links
- 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis. Includes adaptive optics images, orbit diagrams, and shape models.
- (121) Hermione, datasheet, johnstonsarchive.net
- Asteroids with Satellites, Robert Johnston, johnstonsarchive.net
- Tally of Asteroids Harboring Moons Grows Beyond 30 (Space.com, 3 October 2002)
- 121 Hermione at AstDyS-2, Asteroids—Dynamic Site
- 121 Hermione at the JPL Small-Body Database
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