121 Hermione

121 Hermione

121 Hermione (pronEng|hɚˈmaɪəni "hər-mye'-ə-nee") is a very large asteroid of the dark C spectral type, orbiting in the Cybele group in the far outer main belt. As a C-type, it is probably composed of carbonaceous materials.

Hermione was discovered by J. C. Watson on May 12, 1872, and named after Hermione, daughter of Menelaus and Helen in Greek mythology. Hermione is a Cybele asteroid and orbits beyond most of the main belt asteroids.

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 . 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 . 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 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 . For the best-fit "snowman" model, the density is found to be 1.8 ± 0.2 g/cm³, giving a porosity of the order of 20%, and possibly indicating that the main components are fractured solid bodies, but that the asteroid is rather not a rubble pile.

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

atellite (S/2002 (121) 1)

A satellite of Hermione was discovered in 2002 with the Keck II telescope. The satellite is currently 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. Infobox Planet
name=S/2002 (121) 1
width=28em
discovery=yes
physical_characteristics = yes
bgcolour=#A0FFA0
minorplanet=yes
discovery_ref = [http://cfa-www.harvard.edu/iauc/07900/07980.html#Item2 IAUC 7980] ]
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=28 September, 2002
mp_category=Main belt (Cybele)
orbit_ref=" [http://astron.berkeley.edu/~fmarchis/Science/Asteroids/Hermione.html 121 Hermione and S/2002 (121) 1] ", orbit data website maintained by F. Marchis.]
semimajor= 768 ± 11 km
eccentricity= 0.001 ± 0.001
period=2.582 ± 0.002 d
avg_speed=22 m/s
satellite_of = 121 Hermione
inclination = 3 ± 2°
with respect to Hermione pole
dimensions= 12 ± 4 km
mass = ~1.6e|15 kg Assuming a similar density to the primary.]
escape_velocity= ~ 6 m/s
abs_magnitude=13.0
Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0 | minorplanet=yes | width=25em
name=121 Hermione
discovery_ref = [ [http://cfa-www.harvard.edu/iau/lists/NumberedMPs.html Discovery Circumstances: Numbered Minor Planets] , Minor Planet Centre]
discoverer=James Craig Watson
discovered=May 12, 1872
alt_names = 1970 VE
mp_category=Main belt (Cybele)
orbit_ref = [ [ftp://ftp.lowell.edu/pub/elgb/astorb.html ASTORB] orbital elements database, Lowell Observatory]
epoch=December 31, 2006 (JD 2454100.5)
semimajor=517.179 Gm (3.457 AU)
perihelion=446.029 Gm (2.982 AU)
aphelion=588.328 Gm (3.933 AU)
eccentricity=0.138
period=2347.854 d (6.43 a)
inclination=7.604°
asc_node=73.209°
arg_peri=296.215°
mean_anomaly=248.068°
avg_speed=15.94 km/s
satellites = S/2002 (121) 1
dimensions=254±4 × 125±9 km cite journal|author=F. Marchis "et al"|title="Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey"|journal=Icarus|volume=185|pages=39|year=2006|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006Icar..185...39M&db_key=AST&data_type=HTML&format=&high=444b66a47d32271|doi=10.1016/j.icarus.2006.06.001]
mean_radius = 95 km
mass=5.4 ± 0.3e|18 kg cite journal|author=F. Marchis "et al"|title="Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit"|journal=Icarus|volume=178|pages=450|year=2005|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..178..450M&db_key=AST&data_type=HTML&format=&high=444b66a47d32271|doi=10.1016/j.icarus.2005.05.003]
density=1.8 ± 0.2 g/cm³Using the "snowman" shape model, which best matches the value of J2 implied from precession.]
surface_grav=0.022 m/s²On the extremities of the long axis.]
escape_velocity=0.075 km/s
sidereal_day =0.2313 d (5.551 h)" [http://cfa-www.harvard.edu/iauc/08200/08264.html#Item1 IAUC 8264] "]
axial_tilt = 73°
pole_ecliptic_lat = +10 ± 2°
pole_ecliptic_lon = 1.5 ± 2°
temperatures=yes
temp_name1 = Kelvin
mean_temp_1 = ~152
max_temp_1 = 231
temp_name2 = Celsius
max_temp_2 = -44°
albedo= 0.0482 ± 0.002 " [http://www.psi.edu/pds/resource/imps.html Supplemental IRAS minor planet survey] "]
spectral_type = C " [http://www.psi.edu/pds/resource/taxonomy.html PDS node taxonomy database] "]
abs_magnitude=7.31

References

External links

*" [http://astron.berkeley.edu/~fmarchis/Science/Asteroids/Hermione.html 121 Hermione and S/2002 (121) 1] ", orbit data website maintained by F. Marchis. Includes adaptive optics images, orbit diagrams, and shape models.
* [http://www.johnstonsarchive.net/astro/astmoons/am-00121.html Data on (121) Hermione from Johnston's archive] (maintained by W. R. Johnston)
*" [http://www.space.com/scienceastronomy/asteroid_moons_021003.html Tally of Asteroids Harboring Moons Grows Beyond 30] " (Space.com, 3 October, 2002)


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