(87) Sylvia

Asteroid (87) Sylvia

Asteroid Sylvia with two moons (ESO / VLT)
Properties of the orbit ( animation ) Epoch: 4th September 2017 ( JD 2,458,000.5)
Orbit type	Outer main belt of the Cybele group
Asteroid family	Sylvia family
Major semi-axis	3.4812 AU
eccentricity	0.0926
Perihelion - aphelion	3.1590 AU - 3.8035 AU
Inclination of the orbit plane	10.877 °
Length of the ascending node	73.051 °
Argument of the periapsis	263.529 °
Time of passage of the perihelion	23rd August 2017
Sidereal period	6 a 182.5 d
Mean orbital velocity	15.94 km / s
Physical Properties
Medium diameter	253.0 ± 3.0 km
Dimensions	385 × 265 × 230 km
Dimensions	1.48 x 10 ¹⁹ kg
Albedo	0.046 ± 0.004
Medium density	1.2 g / cm³
Rotation period	5 h 11 min
Absolute brightness	6.94 mag
Spectral class	P
history
Explorer	Norman R. Pogson
Date of discovery	May 16, 1866
Another name	A909 GA
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.

(87) Sylvia is an asteroid that moves in the outer reaches of the main asteroid belt . With a mean diameter of 253 km, Sylvia is the eighth largest asteroid in the main belt.

Discovery and naming

Sylvia was born on 16 May 1866 by the British astronomer Norman Pogson Robert at the Observatory of Chennai (Madras) in India discovered. The discovery was announced in June 1866.

The asteroid was named after Rhea Silvia , the mother of Romulus and Remus in Roman mythology .

A. Paluzie-Borrell incorrectly wrote in Paul Ergets The Names of the Minor Planets (1955) that the name was chosen in honor of Sylvie Petiaux-Hugo Flammarion, the first wife of the French astronomer Camille Flammarion . But discoverer Norman Pogson wrote in his discovery announcement that the name actually refers to the mythological figure Rhea Silvia.

In total, the asteroid has been observed by several earth-based telescopes, a total of 2862 times within 122 years. (As of Sept. 2017)

Track properties

Orbit

Sylvia orbits the sun in a prograde , elliptical orbit between 472,500,000 km (3.20 AU ) and 569,000,000 km (3.80 AU) from its center. The orbital eccentricity is 0.093, the web is at 11 ° to the ecliptic inclined . Its orbit is therefore in the outer asteroid belt .

The orbital period of Sylvia is 6.50 years.

rotation

Sylvia rotates around its axis once every 5 hours and 11 minutes. From this it follows that the asteroid performs 10,983.6 self- rotations ("days") in a Sylvia year . The orbital speed at the equator is 230 km / h.

Observations of the light curve show an alignment of Sylvias Pol in the direction of the ecliptic coordinates with only 0.5 ° uncertainty; this results in an axis inclination of 29.1 °; Sylvia's rotation is therefore as their orbit prograde . ${\ displaystyle (\ beta, \ lambda) = (+ 62.6 ^ {\ circ}, 72.4 ^ {\ circ})}$

Sylvia family

(87) Sylvia is the namesake of an asteroid family within the Cybele group with similar orbital elements and a predominantly similar mineralogical composition.

Asteroids of the Cybele group move beyond the Hecuba gap with orbital semi-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.

Physical Properties

size

The observations made so far indicate an elongated, irregularly shaped body; the most precise determination of the diameter ( geometric mean ) is 253.051 km. With regard to the exact dimensions, the most precise value is 385 × 262 × 232 km.

Assuming an average diameter of 253 km, this results in a surface area of around 201,000 km ² , which is just about the size of Belarus .

Provisions of the diameter for Sylvia

year	Dimensions km	source
2001	260.9	Tedesco ( IRAS ) u. a.
2005	271 ± 13.3	Marchis et al. a.
2005	289 ± 11	Marchis et al. a.
2005	385 × 265 × 230 ± 10	Marchis et al. a.
2006	348 ± 1 × 217 ± 6	Marchis et al. a.
2006	282	Marchis et al. a.
2014	253.051 ± 2.953	Masiero et al. a.
2016	385 × 262 × 232	Yu Jiang et al. a.

The most precise determination is marked in bold .

internal structure

Sylvia belongs to the X – type asteroids (according to another classification: P) and therefore has a dark, carbon-rich surface with an albedo of 0.05. The surface color is therefore darker than coal. The unusually low mean density of 1.2 g / cm ³ indicates that the celestial body is porous and therefore a rubble pile , a loose collection of dust and rocks. It is believed that the voids may constitute 25% up to 60% of the body, depending on its exact composition; however, the mineralogy of X-type asteroids is not yet sufficiently known to determine this more precisely.

The mass of Sylvia could previously be calculated to be 1.48 ∙ 10 ¹⁹ . The absolute brightness is given as 6.94 mag.

The mean surface temperature is around 151 K (−122 ° C) and can rise to a maximum of 223 K (−50 ° C) at noon.

The Sylvia triple system

Sylvia and her moons

On February 23, 2001, a first companion was discovered with Sylvia at the Keck Observatory with the help of adaptive optics . The moon, initially designated as S / 2001 (87) 1 , has a diameter of 10.8 km and orbits Sylvia at a distance of 1,354 km in 3.65 days.

Through further observations with the Very Large Telescope in 2004, another companion could be found, which was named S / 2004 (87) 1 . This orbits Sylvia within the orbit of the outer moon and is 10.6 km tall; it moves around the asteroid at a distance of 702 km in 33 hours.

Both objects orbit the asteroid at regular intervals on almost circular (eccentricities less than 0.01) and approximately equatorial (orbit inclination less than 2 °) orbits. As a fitting name for the two satellites in 2005 the names were Romulus and Remus by the International Astronomical Union defined (IAU).

Sylvia is the first asteroid to have two moons detected. Other asteroids with two moons are now known. It is now assumed that multiple systems are not uncommon in the solar system.

The Sylvia 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 Sylvia's equator	Date of discovery Date of publication
(87) Sylvia	253.0	100.00	1.5 · 10 ¹⁹	-	-	-	-	May 16, 1866 48660600 ♠June 1866
Remus (Sylvia II)	10.6	3.7	7.3 · 10 ¹⁴	701.64	1.373	0.093	2.0	August 9, 2004 50050810 ♠August 10, 2005
Romulus (Sylvia I)	10.8	3.8	9.3 · 10 ¹⁴	1351.35	3,654	0.007	1.7	February 18, 2001 50010223 ♠February 23, 2001

Web links

Wm. Robert Johnston: (87) Sylvia, Romulus and Remus (English)
Asteroid (87) Sylvia Rotatable 3D model of Sylvia (English)
Asteroids in a pack of three. On: Wissenschaft.de from August 11, 2005.
The moonlets of asteroid 87 Sylvia (English)
Letter to Nature - Discovery of the triple asteroidal system 87 Sylvia (English)

Individual evidence

^ Discovery Circumstances: Numbered Minor Planets. The international Astronomical Union - Minor Planet Center, accessed August 7, 2020 .
↑ (87) Sylvia in the Small-Body Database of the Jet Propulsion Laboratory (English).
↑ IRAS (2001): The Supplemental IRAS Minor Planet Survey. Retrieved September 13, 2017 .
↑ Franck Marchis et al. a .: Discovery and characterization of binary asteroids 22 Kalliope and 87 Sylvia . bibcode : 2001DPS .... 33.5202M .
↑ Franck Marchis et al. a .: Discovery of the triple asteroidal system 87 Sylvia . 2005, PMID 16094362 .
↑ Jim Baer: Recent Asteroid Mass Determinations (2010). (No longer available online.) Archived from the original on July 8, 2013 ; accessed on September 4, 2017 .
^ ^A ^b Franck Marchis et al .: Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey . 2006, PMC 2600456 (free full text).
↑ Joseph R. Masiero et al. a .: Main-belt Asteroids with WISE / NEOWISE: Near-infrared Albedos . 2014, bibcode : 2014ApJ ... 791..121M .
↑ Yu Jiang et al. a .: Dynamical Configurations of Celestial Systems Comprised of Multiple Irregular Bodies (2016). Retrieved September 4, 2017 .

[1] Discovery Circumstances: Numbered Minor Planets. The international Astronomical Union - Minor Planet Center, accessed August 7, 2020 .

[JPL-2] (87) Sylvia in the Small-Body Database of the Jet Propulsion Laboratory (English).

[iras-3] IRAS (2001): The Supplemental IRAS Minor Planet Survey. Retrieved September 13, 2017 .

[marchis1-4] Franck Marchis et al. a .: Discovery and characterization of binary asteroids 22 Kalliope and 87 Sylvia . bibcode : 2001DPS .... 33.5202M .

[marchis2-5] Franck Marchis et al. a .: Discovery of the triple asteroidal system 87 Sylvia . 2005, PMID 16094362 .

[baer-6] Jim Baer: Recent Asteroid Mass Determinations (2010). (No longer available online.) Archived from the original on July 8, 2013 ; accessed on September 4, 2017 .

[marchis3-7] A ^b Franck Marchis et al .: Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey . 2006, PMC 2600456 (free full text).

[Masiero-8] Joseph R. Masiero et al. a .: Main-belt Asteroids with WISE / NEOWISE: Near-infrared Albedos . 2014, bibcode : 2014ApJ ... 791..121M .

[jiang-9] Yu Jiang et al. a .: Dynamical Configurations of Celestial Systems Comprised of Multiple Irregular Bodies (2016). Retrieved September 4, 2017 .