20 Massalia

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20 Massalia
Discovery
Discovered by Annibale de Gasparis
Discovery time September 19, 1852
Names
Other names none
Group Main belt (Massalia family)
Orbit
Reference date October 22, 2004 (JD 2453300.5)
Longest distance from the Sun 411.911 Gm (2.753 AU)
Shortest distance from the Sun 308.699 Gm (2.064 AU)
Longest distance from the center of its orbital path
("semi-major axis")
360.305 Gm (2.408 AU)
How egg-shaped its orbit is
("eccentricity")
0.143
How long it takes to complete an orbit 1365.261 d (3.74 a)
Average speed 19.09 km/s
Mean anomaly 161.641°
Angle above the reference plane
("inclination")
0.707°
Longitude of where it comes up through the reference plane 206.530°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
255.578°
Size and Other Qualities
Measures 160×145×130 km [1][2]
Mass 5.2×1018 kg [3]
Average density 3.2 g/cm³
Gravity at its surface 0.054 m/s²
Slowest speed able to escape into space
("escape velocity")
0.093 km/s
How long it takes to turn around one time 0.3374 d (8.098 h) [4]
How much light it reflects 0.210 (geometric)[1]
Avg. surface temp. ~174 K
max: 265 K (-8°C)
Light-band group
("spectral type")
S [5]
Seeming brightness
("apparent magnitude")
8.3[6] to 12.0
True brightness
("absolute magnitude")
6.50
Seeming size
("angular diameter")
0.186" to 0.058"

20 Massalia is a big and fairly bright Main belt asteroid. It is also the biggest member of the Massalia family of asteroids.

Characteristics[change | change source]

Massalia is an S-type asteroid. It orbits at very low inclination in the intermediate main belt, and is by far the biggest asteroid in the Massalia family. The remaining family members are pieces blown off by a cratering event on Massalia [7]

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, which is rare among asteroids of its size. Apart from the few biggest bodies over 400 km in diameter, such as 1 Ceres and 4 Vesta, most asteroids appear to have been fractured a lot.

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.[2] 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.

Discovery[change | change source]

Massalia was found 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).

References[change | change source]

  1. 1.0 1.1 Supplemental IRAS Minor Planet Survey[dead link]
  2. 2.0 2.1 M. Kaasalainen et al. (2002). "Models of Twenty Asteroids from Photometric Data". Icarus 159: 369. http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf.
  3. J. Bange (1998). "An estimation of the mass of asteroid 20-Massalia derived from the HIPPARCOS minor planets data". Astronomy & Astrophysics 340: L1. Archived from the original on 2012-02-12. http://www.webcitation.org/65OTHDg6u.
  4. PDS lightcurve data[dead link]
  5. PDS spectral class data Archived 17 January 2010 at WebCite
  6. Donald H. Menzel and Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd edition ed.). Boston, MA: Houghton Mifflin. p. p. 391. ISBN 978-0-395-34835-2 .
  7. D. Vokrouhlický et al. (2006). "Yarkovsky/YORP chronology of asteroid families". Icarus 182: 118.

Other websites[change | change source]