121 Hermione

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121 Hermione
Hermione06 2.jpg
121 Hermione and its moon
Discovery [1]
Discovered by James Craig Watson
Discovery date12 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 145.96 yr (53,312 d)
Aphelion 3.9067 AU
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°
Known satellites 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]
Mean density
1.8 ± 0.2 g/cm3 [7] [a]
Equatorial surface gravity
0.022 m/s2 [b]
Equatorial escape 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 binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt. [11] 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. [11]

    Contents

    Discovery

    Hermione was discovered by J. C. Watson on 12 May 1872 from Ann Arbor, Michigan, in the United States, [11] and named after Hermione, daughter of Menelaus and Helen in Greek mythology. [3]

    Physical properties

    Lightcurve-based 3D-model of Hermione 121Hermione (Lightcurve Inversion).png
    Lightcurve-based 3D-model of Hermione

    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. [6] 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. [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 simple ellipsoid 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 a rubble pile.

    Occultations by Hermione have been successfully observed three times so far, the last time in February 2004.

    S/2002 (121) 1
    Discovery [12]
    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 date2002-09-28
    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]

      Moon

      A satellite of Hermione was discovered in 2002 with the Keck II telescope. [11] It is about 8 miles (13 km) in diameter. [11] 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. [14] [6]

      Notes

      1. ↑ Using the "snowman" shape model, which best matches the value of J2 implied from precession.
      2. 1 2 On the extremities of the long axis.
      3. ↑ Assuming a similar density to the primary.

      References

      1. ↑ "121 Hermione". Minor Planet Center. Retrieved 14 September 2018.
      2. ↑ Noah Webster (1884) A Practical Dictionary of the English Language
      3. 1 2 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.
      4. ↑ "JPL Small-Body Database Browser: 121 Hermione" (2018-05-25 last obs.). Jet Propulsion Laboratory . Retrieved 14 September 2018.
      5. ↑ Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. Archived from the original on 2 July 2013. Retrieved 7 December 2008.
      6. 1 2 3 4 5 6 F. Marchis; et al. (2006). "Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey". Icarus. 185 (1): 39–63. Bibcode:2006Icar..185...39M. doi:10.1016/j.icarus.2006.06.001. PMC   2600456 . PMID   19081813.
      7. 1 2 3 4 5 6 F. Marchis; et al. (2005). "Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit". Icarus. 178 (2): 450–464. Bibcode:2005Icar..178..450M. doi:10.1016/j.icarus.2005.05.003.
      8. ↑ IAUC 8264 Archived 9 July 2008 at the Wayback Machine
      9. 1 2 Supplemental IRAS minor planet survey Archived 2009-08-17 at the Wayback Machine
      10. ↑ PDS node taxonomy database Archived 2009-08-05 at the Wayback Machine
      11. 1 2 3 4 5 Linda T. Elkins-Tanton (2010). Asteroids, Meteorites, and Comets. Infobase Publishing. p. 96. ISBN   978-1-4381-3186-3.
      12. ↑ IAUC 7980 Archived 2006-05-01 at the Wayback Machine
      13. ↑ 121 Hermione and S/2002 (121) 1 , orbit data website maintained by F. Marchis.
      14. ↑ Johnston, Wm. Robert (21 September 2014). "(121) Hermione and S/2002 (121) 1 ("LaFayette")". Asteroids with Satellites Database. Johnston's Archive. Retrieved 7 November 2021.
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