Astronomy:121 Hermione

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121 Hermione
Hermione06 2.jpg
121 Hermione and its moon
Discovery[1]
Discovered byJames Craig Watson
Discovery date12 May 1872
Designations
(121) Hermione
Pronunciation/hɜːrˈmaɪ.əniː/[3]
Named afterHermione[2]
(Greek mythology)
A872 JA; 1970 VE
Minor planet categorymain-belt · Cybele
AdjectivesHermionean /hɜːrmaɪ.əˈniːən/
Orbital characteristics[4]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc145.96 yr (53,312 d)
|{{{apsis}}}|helion}}3.9067 AU
|{{{apsis}}}|helion}}2.9889 AU
3.4478 AU
Eccentricity0.1331
Orbital period6.40 yr (2,338 d)
Mean anomaly157.08°
Mean motion0° 9m 14.4s / day
Inclination7.5975°
Longitude of ascending node73.127°
298.18°
Known satellitesS/2002 (121) 1
Physical characteristics
Mean radius95 km[5]
Mass5.38 ± 0.3 ×1018 kg[6]
5.4 ± 0.3×1018 kg[7]
Mean density1.13 ± 0.3 g/cm3[6]
1.8 ± 0.2 g/cm3[7][8]
Equatorial surface gravity
0.022 m/s2[9]
Equatorial escape velocity
0.075 km/s[9]
Sidereal rotation period0.2313 d (5.551 h)[10]
Axial tilt73°
Pole ecliptic latitude+10 ± 2°[7]
Pole ecliptic longitude1.5 ± 2°
Geometric albedo0.0482 ± 0.002[11]
C[12]
Absolute magnitude (H)7.31[11]


Hermione (minor planet designation: 121 Hermione) is a very large binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt.[13] 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.[13]

Discovery

Hermione was discovered by J. C. Watson on 12 May 1872 from Ann Arbor, Michigan, in the United States,[13] and named after Hermione, daughter of Menelaus and Helen in Greek mythology.[2]

Physical properties

thumb|left|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.[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.[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[14]
Discovered byW. 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
Minor planet categorymain-belt · Cybele
Orbital characteristics[15]
768 ± 11 km
Eccentricity0.001 ± 0.001
Orbital period2.582 ± 0.002 d
Inclination3 ± 2°
(with respect to Hermione pole)
Satellite of121 Hermione
Physical characteristics
Dimensions12 ± 4 km[5]
Mass~1.6×1015 kg[16]
Absolute magnitude (H)13.0[5]


Moon

A satellite of Hermione was discovered in 2002 with the Keck II telescope.[13] It is about 8 miles (13 km) in diameter.[13] 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.[17][5]

References

  1. ↑ "121 Hermione". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=121. Retrieved 14 September 2018. 
  2. ↑ 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. 
  3. ↑ Noah Webster (1884) A Practical Dictionary of the English Language
  4. ↑ "JPL Small-Body Database Browser: 121 Hermione". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000121. Retrieved 14 September 2018. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Cite error: Invalid <ref> tag; no text was provided for refs named MarKaaHom06
  6. ↑ 6.0 6.1 Cite error: Invalid <ref> tag; no text was provided for refs named Baer
  7. ↑ 7.0 7.1 7.2 7.3 7.4 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. 
  8. ↑ Using the "snowman" shape model, which best matches the value of J2 implied from precession.
  9. ↑ 9.0 9.1 On the extremities of the long axis.
  10. ↑ IAUC 8264
  11. ↑ 11.0 11.1 Supplemental IRAS minor planet survey
  12. ↑ PDS node taxonomy database
  13. ↑ 13.0 13.1 13.2 13.3 13.4 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. 
  14. ↑ IAUC 7980
  15. ↑ 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis.
  16. ↑ Assuming a similar density to the primary.
  17. ↑ 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



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