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24 Themis (thee'-mis, them'-is) is one of the largest Main belt asteroids. It is also the largest member of Themistian asteroid family.

24 Themis
Discovery A
Discoverer Annibale de Gasparis
Discovery date April 5, 1853
Alternate
designations
1947 BA; 1955 OH B
Category Main belt (Themis)
Orbital elements C D
Epoch August 18, 2005 (JD 2453600.5)
Eccentricity (e) 0.132
Semi-major axis (a) 468.226 Gm (3.130 AU)
Perihelion (q) 406.202 Gm (2.715 AU)
Aphelion (Q) 530.250 Gm (3.545 AU)
Orbital period (P) 2022.524 d (5.54 a)
Mean orbital speed 16.76 km/s
Inclination (i) 0.760°
Longitude of the
ascending node (Ω))
35.992°
Argument of
perihelion (ω)
107.989°
Mean anomaly (M) 185.968°
Physical characteristics
Dimensions 228 km
Mass 5.75—1019 kg [1]
Density 9.6 g/cm³
Surface gravity 0.3059 m/s²
Escape velocity 0.2641 km/s
Rotation period 0.34892 d (8 h 23 min) [2] [3]
Spectral class C [4]
Absolute magnitude 7.08
Albedo 0.067 [5]
Mean surface
temperature
~159 K

It was discovered by Annibale de Gasparis on April 5, 1853. The mass and diameter appearing in the table are from separate sources, and combining them gives an unusually large density, which is most probably wrong. The mass has very likely been overestimated by a factor of at least five times.

It is named after Themis, the personification of divine order, law and custom in Greek mythology.

Themis was also the name given to the spurious lost "tenth" satellite of Saturn that William Henry Pickering believed he had found in 1905. [6]

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