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20 Massalia (pronounced /məˈseɪliə/ mə-SAY-lee-ə, or as in Greek: Μασσαλία) is a large and fairly bright Main belt asteroid. It is also the largest member of the Massalia family of asteroids.


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.[8]

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.[4] The mass of Massalia is dependent on the mass of 4 Vesta and perturbation of 44 Nysa.[4]

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.[3] 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.


Massalia was discovered by A. de Gasparis on September 19, 1852, and also found independently the next night by J. Chacornac. It was Chacornac's discovery that was announced first.

Massalia is the Greek name for Marseille, where Chacornac made his discovery (de Gasparis was observing from Naples).

In the nineteenth century the variant spelling "Massilia" was often used.


1. ^ a b c Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. http://home.earthlink.net/~jimbaer1/astmass.txt. Retrieved 2008-12-11.
2. ^ a b Supplemental IRAS Minor Planet Survey
3. ^ a b M. Kaasalainen et al. (2002). "Models of Twenty Asteroids from Photometric Data" (PDF). Icarus 159: 369. doi:10.1006/icar.2002.6907. http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf.
4. ^ a b c J. Bange (1998). "An estimation of the mass of asteroid 20-Massalia derived from the HIPPARCOS minor planets data". Astronomy & Astrophysics 340: L1. http://articles.adsabs.harvard.edu//full/seri/A%2BA../0340//L000001.000.html.
5. ^ PDS lightcurve data
6. ^ PDS spectral class data
7. ^ Donald H. Menzel and Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd ed.). Boston, MA: Houghton Mifflin. pp. 391. ISBN 0395348358.
8. ^ D. Vokrouhlický et al. (2006). "Yarkovsky/YORP chronology of asteroid families". Icarus 182: 118. doi:10.1016/j.icarus.2005.12.010.

External links

* shape model deduced from lightcurve
* Orbital elements for bright asteroids from the Minor Planet Center.
* Orbital simulation from JPL (Java) / Ephemeris

Astronomy Encyclopedia

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