S / 2002 (121) 1

(121) Hermione I (S / 2002 (121) 1) 1)

S / 2002 (121) 1 and Hermione in December 2003 with the Keck telescope .
Provisional or systematic name	S / 2002 (121) 1
Central body	(121) Hermione
Properties of the orbit
Major semi-axis	747 ± 11 km
Periapsis	747 km
Apoapsis	747 km
eccentricity	0.001 ± 0.001
Orbit inclination	3.0 ± 2.0 °
Orbital time	2.5630 ± 0.0021 d
Mean orbital velocity	0.022 km / s
Physical Properties
Apparent brightness	13.6 mag
Medium diameter	32.0 km
Dimensions	~ 1.6 · 10 ¹⁵ kg
surface	3200 km ²
Medium density	≈ 1.4 ± 0.35 g / cm ³
Escape speed	~ 6 m / s
Surface temperature	152 K
discovery
Explorer	William J. Merline Peter M. Tamblyn Christophe Dumas Laird M. Close Clark R. Chapman François Menard W. M. Owen David C. Slater J. Pepin
Date of discovery	September 28, 2002
Remarks	Largest moon in the asteroid belt

S / 2002 (121) 1 is a moon of the main belt asteroid (121) Hermione ( Cybele Group ). Its mean diameter is 32 kilometers, making it the largest asteroid in the main belt.

Discovery and naming

S / 2002 (121) 1 was published on September 28, 2002 by William J. Merline, Peter M. Tamblyn, Christophe Dumas, Laird M. Close, Clark R. Chapman, François Menard, WM Owen, David C. Slater and J. Pepin was discovered using adaptive optics with the 10 m Keck Telescope II on Mauna Kea in Hawaii . The discovery was announced two days later on September 30, 2002; the moon was given the provisional designation S / 2002 (121) 1 .

The name "LaFayette" was proposed for the moon after Marie-Joseph Motier, Marquis de La Fayette , who secretly went to Boston in 1780 with the frigate Hermione to help the rebel colonists against the British in the American War of Independence .

An official name confirmation from the IAU is still pending; since there is also an asteroid named (23244) Lafayette , a name under this name is questionable. According to NASA , the name "Harry" is also among the candidates.

Track properties

S / 2002 (121) 1 orbits Hermione on a prograde , almost perfect circular path at an average distance of 747 kilometers from its center (about 8 Hermione radii). The orbit eccentricity is 0.00, the orbit is inclined 3 ° to the Hermione equator .

S / 2002 (121) 1 orbits Hermione in 2 days, 13 hours and 31 minutes, which corresponds to about 912 orbits in one Hermione year (about 6.4 earth years). The orbit of S / 2002 (121) 1 is assumed to be stable because it is well within Hermione's Hill radius of 41,000 km, but also well outside of the synchronous orbit.

Physical Properties

size

According to current data, S / 2002 (121) 1 has a diameter of 32 km (almost 1/6 of the central body), based on Hermione's density and the corresponding assumed equal reflectivity of 5%. The surface is therefore extremely dark. On the basis of the data so far, however, the determination of the diameter still seems relatively uncertain; it currently ranges from 12 to 32 km.

S / 2002 (121) 1 is currently the largest moon in the asteroid belt, even ahead of Linus (28 km); in this respect it is only surpassed by the Antiope moon S / 2000 (90) 1 (84 km). However, this system must be viewed as a double system, since S / 2000 (90) 1 has 95.4% of the diameter of Antiope and the barycentre is therefore outside the main body.

If one adds the Jupiter Trojans to the belt, then only the double system Patroclus / Menoetius would be added; Menoetius would be the largest moon in the inner solar system at 113 km, and S / 2002 (121) 1 - including the Antiope system - would slide to third place.

Assuming an average diameter of 32 km, this results in a surface area of around 3,200 km ² , which corresponds to the area of the Swiss canton of Vaud .

Determination of the diameter for S / 2002 (121) 1

year	Dimensions km	source
2002	13	Knocke ( NASA )
2006	12 ± 4	Marchis et al.
2009	32	Descamps et al.

The most recent determination is marked in bold .

internal structure

Since S / 2002 (121) 1 has a similar color to the mother body, it is assumed that the moon is made of the same material as Hermione and therefore has the same spectral type (C or Ch). Based on the same density and albedo, the mass could so far be calculated to be about 1.6 · 10 ¹⁵ .

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).

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

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

↑ ^a ^b Melanie Melton Knocke: NASA: Asteroid 121 Hermione's Unusual Companion. (No longer available online.) Formerly in the original ; accessed on September 10, 2017 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2
^ F. Marchis, M. Kaasalainen, EF Hom, J. Berthier, J. Enriquez, D. Hestroffer, D. Le Mignant, I. de Pater: Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey . In: Icarus. Volume 185, number 1, November 2006, pp. 39-63, doi : 10.1016 / j.icarus.2006.06.001 , PMID 19081813 , PMC 2600456 (free full text).
^ Pascal Descamps et al .: New insights on the binary asteroid 121 Hermione . April 2009, arxiv : 0904.2033 .

[iauc7980-1] Daniel WE Green: IAUC No. 7980: S / 2002 (121) 1 discovery publication. Retrieved September 10, 2017 .