(121) Hermione

Asteroid (121) Hermione

Hermione and her moon S / 2002 (121) 1 in December 2003 with the Keck telescope .
Properties of the orbit ( animation ) Epoch: 4th September 2017 ( JD 2,458,000.5)
Orbit type	Outer main belt of the Cybele group
Major semi-axis	3.4471 AU
eccentricity	0.1334
Perihelion - aphelion	2.9873 AU - 3.9070 AU
Inclination of the orbit plane	7.598 °
Length of the ascending node	73.131 °
Argument of the periapsis	298.191 °
Time of passage of the perihelion	June 7, 2015
Sidereal period	6 a 148 d
Mean orbital velocity	15.94 km / s
Physical Properties
Medium diameter	187 ± 6 km
Dimensions	254 ± 4 × 125 ± 9
Dimensions	4.7 ± 0.2 x 10 ¹⁸ kg
Albedo	0.0482 ± 0.002
Medium density	1.4 ± 0.35 g / cm³
Rotation period	5 h 33 min 4.6 s
Absolute brightness	7.31 mag
Spectral class (according to Tholen)	C.
Spectral class (according to SMASSII)	Ch
history
Explorer	James C. Watson
Date of discovery	May 12, 1872
Another name	1970 VE
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . The affiliation to an asteroid family is automatically determined from the AstDyS-2 database . Please also note the note on asteroid items.

(121) Hermione is an asteroid located in the main outer asteroid belt . With a diameter of 187 km it is one of the largest asteroids in the main belt and it has a comparatively large moon called S / 2002 (121) 1 .

Discovery and naming

Hermione was discovered on May 12, 1872 by the American astronomer James Craig Watson in Ann Arbor , Michigan ( USA ).

The celestial body was named after Hermione , the daughter of the Spartan king Menelaus and Helena from Greek mythology at the time of the Trojan War .

In total, the asteroid was observed through several earth-based telescopes, a total of 2607 times in 144 years. (As of Sept. 2017)

Track properties

Orbit

Hermione orbits the sun in a prograde , elliptical orbit between 446,900,000 km (2.99 AU ) and 584,500,000 km (3.91 AU) from its center. The orbital eccentricity is 0.134, the web is about 7.6 ° relative to the ecliptic inclined . Its orbit is therefore in the outer asteroid belt .

The orbital period of Hermione is 6.40 years.

Hermione belongs to the Cybele Group , a number of asteroids that orbit beyond the Hecuba Gap with orbital axes between 3.27 and 3.7 AU. The objects have eccentricities of less than 0.3 and orbit inclinations of less than 25 °. The members of this group are in 7: 4 resonance with Jupiter, which stabilizes their orbit. They are likely fragments of a previous collision.

rotation

Hermione rotates once around its axis in 5 hours, 33 minutes 5 seconds. From this it follows that the asteroid performs 10,106.6 self- rotations ("days") in one Hermione year .

Physical Properties

Hermione in a 3D model

size

The observations made so far indicate an irregularly shaped, elongated body; the most precise determination of the diameter ( geometric mean ) is 187 km. With regard to the exact dimensions, the most precise value is 254 × 125 km.

According to observations made with the 10 m Keck Telescope II using adaptive optics in December 2003, Hermione appears to consist of two components adhering to one another. Of several matching models, this “snowman” shape best fits the observed rate of precession of Hermione's moon. In this model, the shape of Hermiones consists of two round bodies overlapping by 5 km with diameters of 160 and 120 km, the centers of which are separated by 115 km. A simple ellisoidal shape was excluded.

Assuming a mean diameter of 187 km, the surface area is around 110,000 km ² , which roughly corresponds to the area of Bulgaria .

Provisions of the diameter for Hermione

year	Dimensions km	source
2000	268 × 186 × 183	Viateau et al.
2002	217	Knocke ( NASA )
2002	209.0 ± 4.7	Tedesco ( IRAS ) et al.
2004	265 × 180 × 180	Lecacheux
2006	190	Marchis et al.
2006	254 ± 4 × 125 ± 9	Marchis et al.
2009	187 ± 6	Descamps et al.

The most precise / most recent determination is marked in bold .

internal structure

Hermione belongs to the C-type asteroids (according to another classification: Ch) and therefore has a dark, carbon-rich surface with an albedo of 0.048; it may consist of primitive carbonaceous chondrites . The density is 1.4-1.8 g / cm ³ . The porosity is estimated to be 20%, which could be an indication that the two main components are solid broken fragments and therefore rather not a rubble pile .

So far, the mass has been calculated to be 4.7 ∙ 10 ¹⁸ . The mean surface temperature is around 152 K (−121 ° C) and can rise to a maximum of 231 K (−42 ° C) at noon; at night it can drop to 73 K (−200 ° C).

Star occultations have been successfully observed three times so far, the last time in February 2004.

moon

On March 28, 2008 the discovery of a moon around Hermione was announced, which was given the provisional designation S / 2002 (121) 1 . The names LaFayette or Harry were suggested for this . The moon has a diameter of 32 kilometers, which makes it (according to the dual system Antiope A and B ) the largest asteroid moon in the main belt. The distance to the main body is given as 747 kilometers.

The Hermione system at a glance:

Components	Physical parameters			Path parameters				discovery
Surname	Throughput diameter (km)	Relative size %	Mass (kg)	Major semi-axis (km)	Orbital time (d)	eccentricity	Inclination to Hermione's equator	Date of discovery Date of publication
(121) Hermione	187.0	100.00	4.7 · 10 ¹⁸	-	-	-	-	May 12, 1872 48720000 ♠1872
S / 2002 (121) 1 (Hermione I)	32.0	17.1	1.6 · 10 ¹⁵	747	2.563	0.001	3 °	September 28, 2002 50020930 ♠September 30, 2002

Web links

Wm. Robert Johnston: (121) Hermione and S / 2002 (121) 1 ("LaFayette") (English)
2004/02/16 (121) Hermione event: a bi-lobated asteroid and its satellite occult TYC 1905-00864-1 Image by Hermione and S / 2002 (121) 1 (English)

Individual evidence

↑ (121) Hermione in the Small-Body Database of the Jet Propulsion Laboratory (English).

^ Franck Marchis et al .: Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit . November 2005, bibcode : 2005Icar..178..450M .

↑ B. Viateau et al .: Mass and density of asteroids (16) and Psyche (121) Hermione . February 2000, bibcode : 2000A & A ... 354..725V .

↑ Melanie Melton Knocke: NASA: Asteroid 121 Hermione's Unusual Companion (2002). (No longer available online.) Formerly in the original ; accessed on September 10, 2017 . ( Page no longer available , search in web archives )@1@ 2

↑ IRAS (2002): IRAS Minor Planet Survey V. 6.0. Retrieved September 10, 2017 .

↑ Jean Lecacheux: 2004/02/16 (121) Hermione occultation: How the satellite track was determined and adjacent problems. Retrieved September 10, 2017 .

^ ^A ^b Franck Marchis et al .: Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey . November 2006, PMC 2600456 (free full text).

^ Pascal Descamps et al .: New insights on the binary asteroid 121 Hermione . April 2009, arxiv : 0904.2033 .

↑ Daniel WE Green: IAUC No. 7980: S / 2002 (121) 1 discovery publication. Retrieved September 10, 2017 .

[JPL-1] (121) Hermione in the Small-Body Database of the Jet Propulsion Laboratory (English).

[marchis2-2] Franck Marchis et al .: Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit . November 2005, bibcode : 2005Icar..178..450M .

[viateau-3] B. Viateau et al .: Mass and density of asteroids (16) and Psyche (121) Hermione . February 2000, bibcode : 2000A & A ... 354..725V .