20 Massalia

20 Massalia

A three dimensional model of 20 Massalia, based on its light curve.
Discovery
Discovered by	Annibale de Gasparis
Discovery date	September 19, 1852
Designations
Pronunciation	/məˈseɪliə/ mə-SAY-lee-ə
Named after	Marseille
Alternative names	none
Minor planet category	Main belt (Massalia family)
Orbital characteristics
Epoch October 22, 2004 (JD 2453300.5)
Aphelion	411.911 Gm (2.753 AU)
Perihelion	308.699 Gm (2.064 AU)
Semi-major axis	360.305 Gm (2.408 AU)
Eccentricity	0.143
Orbital period	1365.261 d (3.74 a)
Average orbital speed	19.09 km/s
Mean anomaly	161.641°
Inclination	0.707°
Longitude of ascending node	206.530°
Argument of perihelion	255.578°
Physical characteristics
Dimensions	160×145×132 km 145 km (mean) 160×145×130 km
Mass	5.67×1018 kg 5.2×1018 kg
Mean density	3.54±0.85 g/cm³
Surface gravity	0.054 m/s²
Escape velocity	0.093 km/s
Rotation period	0.3374 d (8.098 h)
Albedo	0.210 (geometric)
Temperature	~174 K max: 265 K (-8°C)
Spectral type	S
Apparent magnitude	8.3 to 12.0
Absolute magnitude (H)	6.50
Angular diameter	0.186" to 0.058"

20 Massalia is a large and fairly bright main-belt asteroid. It is also the largest member of the Massalia family of asteroids. Its name is the Greek name for Marseille, the city from which one of the two independent co-discovers, Jean Chacornac, first sighted it.

Characteristics

Massalia is an S-type asteroid. It orbits at very low inclination in the intermediate main belt, and is by far the largest asteroid in the Massalia family. The remaining family members are fragments ejected by a cratering event on Massalia.

Massalia has an above-average density for S-type asteroids, similar to the density of silicate rocks. As such, it appears to be a solid un-fractured body, a rarity among asteroids of its size. Apart from the few largest bodies over 400 km in diameter, such as 1 Ceres and 4 Vesta, most asteroids appear to have been significantly fractured, or are even rubble piles. In 1998, Bange estimated Massalia to have a mass of 5.2×10¹⁸ kg assuming that 4 Vesta has 1.35×10⁻¹⁰ solar mass. The mass of Massalia is dependent on the mass of 4 Vesta and perturbation of 44 Nysa.

Lightcurve analysis indicates that Massalia's pole points towards either ecliptic coordinates (β, λ) = (45°, 10°) or (β, λ) = (45°, 190°) with a 10° uncertainty. This gives an axial tilt of 45°in both cases. The shape reconstruction from lightcurves has been described as quite spherical with large planar, nonconvex parts of the surface.

In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty.

Discovery

Massalia was discovered by A. de Gasparis on September 19, 1852 in Naples, and also found independently the next night by J. Chacornac in Marseilles. It was Chacornac's discovery that was announced first. In the nineteenth century the variant spelling Massilia was often used. Asteroids discovered prior to Massalia were assigned iconic symbols, like the ones traditionally used to designate the planets. However, astronomers had begun to phase out this practice with the discovery of 16 Psyche in March 1852, and 20 Massalia (being the first object in the Solar System with a non-mythological name) was the first asteroid that was not assigned an iconic symbol.

External links

• shape model deduced from lightcurve
• Elements and Ephemeris for (20) Massalia from the Minor Planet Center.
• JPL Ephemeris