20 Massalia

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20 Massalia
Lightcurve-based 3D-model of Massalia
Discovered byA. de Gasparis
Discovery siteNaples Obs.
Discovery date19 September 1852
(20) Massalia
Named after
Marseille (French city)[3]
Massilia /mæˈsɪliə/[4]
main belt[1][5] · Massalia[6]
AdjectivesMassalian /mæˈsliən/[2]
Orbital characteristics[5]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc164.08 yr (59,929 d)
Aphelion2.7514 AU
Perihelion2.0662 AU
2.4088 AU
3.74 yr (1,366 d)
0° 15m 48.96s / day
Physical characteristics
Dimensions160×145×132 km[7]
160×145×130 km[8]
Mean diameter
145.50±9.3 km[9]
Mass5.2×1018 kg[10]
5.67×1018 kg[7]
Mean density
3.54±0.85 g/cm3[7]
8.098 h[11]
Tholen = S[5]
SMASS = S[5]
8.3[12] to 12.0
0.186" to 0.058"

Massalia, minor planet designation 20 Massalia, is a stony asteroid and the parent body of the Massalia family located in the inner region of the asteroid belt, approximately 145 kilometers (90 miles) in diameter. Discovered by Italian astronomer Annibale de Gasparis on 19 September 1852, it was named for the French city of Marseille, from which the independent discover Jean Chacornac sighted it the following night.[3]

It comes to opposition 179 degrees from the Sun on 16 June 2023,[13] and will come to aphelion (farthest distance from the Sun) on 17 September 2023.

Classification and orbit[edit]

Massalia is the namesake and the parent body of the Massalia family (404), a very large inner belt asteroid family consisting of stony asteroids with very low inclinations.[6][14]: 23  It is by far the largest body in this family. The remaining family members are fragments ejected by a cratering event on Massalia.[15]

It orbits the Sun in the inner main-belt at a distance of 2.1–2.8 AU once every 3 years and 9 months (1,366 days; semi-major axis of 2.41 AU). Its orbit has an eccentricity of 0.14 and an inclination of 1° with respect to the ecliptic.[5]

Physical characteristics[edit]

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.[10] The mass of Massalia is dependent on the mass of 4 Vesta and perturbation of 44 Nysa.[10]

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.[8] 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.[16]


Massalia was discovered on 19 September 1852, by Annibale de Gasparis at Naples Observatory in Italy, and also found independently the next night by Jean Chacornac at Marseilles Observatory, France. 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)[3] was the first asteroid that was not assigned an iconic symbol.


  1. ^ a b "20 Massalia". Minor Planet Center. Retrieved 29 March 2018.
  2. ^ a b "Messalian, Massalian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  3. ^ a b c Schmadel, Lutz D. (2007). "(20) Massalia". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 17. doi:10.1007/978-3-540-29925-7_21. ISBN 978-3-540-00238-3.
  4. ^ John Craig (1869) The Universal English Dictionary
  5. ^ a b c d e f "JPL Small-Body Database Browser: 20 Massalia" (2018-01-24 last obs.). Jet Propulsion Laboratory. Retrieved 29 March 2018.
  6. ^ a b "Asteroid 20 Massalia". Small Bodies Data Ferret. Retrieved 24 October 2019.
  7. ^ a b c Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. Archived from the original on 2 July 2013. Retrieved 11 December 2008.
  8. ^ a b M. Kaasalainen; et al. (2002). "Models of Twenty Asteroids from Photometric Data" (PDF). Icarus. 159 (2): 369–395. Bibcode:2002Icar..159..369K. doi:10.1006/icar.2002.6907.
  9. ^ a b Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 30 October 2019.
  10. ^ 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. Bibcode:1998A&A...340L...1B.
  11. ^ a b "LCDB Data for (20) Massalia". Asteroid Lightcurve Database (LCDB). Retrieved 29 March 2018.
  12. ^ Donald H. Menzel & Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd ed.). Boston, MA: Houghton Mifflin. pp. 391. ISBN 978-0-395-34835-2.
  13. ^ JPL Horizons (Opposition)
  14. ^ Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families". Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131.
  15. ^ D. Vokrouhlický; et al. (2006). "Yarkovsky/YORP chronology of asteroid families". Icarus. 182 (1): 118–142. Bibcode:2006Icar..182..118V. doi:10.1016/j.icarus.2005.12.010.
  16. ^ Gradie, J.; Flynn, L. (March 1988), "A Search for Satellites and Dust Belts Around Asteroids: Negative Results", Abstracts of the Lunar and Planetary Science Conference, vol. 19, pp. 405–406, Bibcode:1988LPI....19..405G

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