(243) Ida
(243) Ida is a stony (S-type) main-belt asteroid of the Koronis family, about 60 km long and irregularly shaped, imaged up close by NASA's Galileo spacecraft on its way to Jupiter in 1993. Those images revealed that Ida has a small moon, Dactyl — the first satellite ever found around an asteroid.
Key facts
Science
Physical
- Dimensions
- 59.8 × 25.4 × 18.6 km · approx. triaxial diameter
- Rotation period
- 4.63 hours
Orbital
- Semi-major axis
- 2.86 AU
- From catalogued orbital elements (MPC)
- Eccentricity
- 0.04611
- From catalogued orbital elements (MPC)
- Inclination
- 1.13 °
- From catalogued orbital elements (MPC)
- Orbital period
- 4.85 years
- From catalogued orbital elements (MPC)
- Perihelion
- 2.73 AU
- Computed from the orbital elements
- Aphelion
- 3 AU
- Computed from the orbital elements
- Mean orbital velocity
- 17.6 km/s
- Computed from the orbital elements
Discovery
- Discovered
- September 29, 1884
- Discoverer
- Johann Palisa
Composition
- Make-up
- An S-type asteroid of silicate rock (olivine and pyroxene) with some metal, a member of the Koronis collisional family. Its surface is heavily cratered and reddened by space weathering.
Radiation & temperature
- Insolation
- 0.122 S⊕ · 12% of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Geometric albedo
- 0.24
- Geometric (V-band) albedo (Galileo / ground-based).
- Equilibrium temperature
- 154 K (-120 °C)
- Computed from albedo + distance from the Sun (airless black body); uses the geometric albedo as an estimate
Discovery & history
- Discovered
- September 29, 1884
- By
- Johann Palisa
- Method
- Visual (Telescopic)
(243) Ida was discovered on 29 September 1884 by Johann Palisa at the Vienna Observatory, one of the many main-belt asteroids he found. It drew little special attention until NASA's Galileo spacecraft flew past it on 28 August 1993 on the way to Jupiter and returned the first close-up images — which, months later, revealed that Ida has a tiny moon, Dactyl.
Passed 2,410 km away (2,391 km in the mission's reconstruction) and found Ida's moon, Dactyl, in the pictures.
Images
Images from open archives · credit shown per image