258 Tyche

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258 Tyche
Discovery A
Discoverer Robert Luther
Discovery date May 4, 1886
Alternate
designations B		 none
Category Main belt (Eunomia family)
Orbital elements C
Epoch 30 January 2005 (JD 2453400.5)
Eccentricity (e) 0.205
Semi-major axis (a) 391.168 Gm (2.615 AU)
Perihelion (q) 311.048 Gm (2.079 AU)
Aphelion (Q) 471.289 Gm (3.15 AU)
Orbital period (P) 1544.356 d (4.23 a)
Mean orbital speed 18.42 km/s
Inclination (i) 14.293°
Longitude of the
ascending node (Ω)		 207.701°
Argument of
perihelion (ω)		 154.948°
Mean anomaly (M) 258.968°
Physical characteristics D
Dimensions 65 km [1]
Mass ~4×1017 (estimate)
Density ~2.7 g/cm³ (estimate) [2]
Surface gravity ~0.025 m/s² (estimate)
Escape velocity ~0.04 km/s (estimate)
Rotation period 0.417 d (10.0 h) [3] [4]
Spectral class S
Absolute magnitude 8.5
Albedo (geometric) 0.168 [1]
Mean surface
temperature		 ~169 K
max: 268 K (-5°C)
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258 Tyche is a relatively large Main belt asteroid. It is classified as an S-type. Tyche orbits very close to the Eunomia family of asteroids, and could be a member based on composition. However, it is larger than all family members apart from 15 Eunomia while lying at the very edge of the family group. Hence, there is a good chance that it is an unrelated interloper.

There is some uncertainty regarding Tyche's rotation period. Various authors give values from 9.983 to 10.041 hours. [4]

It was discovered by Robert Luther on May 4, 1886 in Düsseldorf and was named after Greek goddess Tyche. Tyche's Roman equivalent is Fortuna, who also has an asteroid named after her (19 Fortuna).

[edit] References

  1. ^ a b Supplemental IRAS Minor Planet Survey
  2. ^ G. A. Krasinsky et al Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
  3. ^ PDS lightcurve data
  4. ^ a b D. Riccioli, C. Blanco, & M. Cigna Rotational periods of asteroids II, Planetary and Space Science, Vol. 49,, p. 657 (2001).
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