Knowra243 Ida243 Ida243 Ida is a stony asteroid in the main belt’s Koronis family. It was discovered in 1884 and has a small moon, Dactyl.BriefConnectDactyl: Dactyl is a small natural satellite orbiting the asteroid 243 Ida. Its discovery in images from Galileo made Ida the first asteroid known to have a moon.Asteroid rotation: Asteroid rotation is the spinning motion of an asteroid around an axis. Ida rotates rapidly enough to help explain its elongated, rubble-like shape.Johann Palisa: Johann Palisa was an Austrian astronomer who discovered numerous asteroids in the nineteenth century. He discovered Ida in 1884 while observing from Vienna.Asteroid moon: An asteroid moon is a natural satellite orbiting an asteroid. Dactyl’s detection at Ida established that asteroid moons could be directly observed.Galileo spacecraft: Galileo was a NASA spacecraft that explored Jupiter and flew past two main-belt asteroids. It returned the images that revealed Dactyl beside Ida in 1993.Rubble-pile asteroid: A rubble-pile asteroid is a gravitationally bound aggregate of fragments rather than a single solid rock. Ida’s craters and irregular form are consistent with a fractured, reaccreted body.Astronomical discovery: Astronomical discovery is the identification and confirmation of previously unknown celestial objects or phenomena. Ida’s discovery illustrates asteroid detection before photographic surveys became routine.Binary asteroid: A binary asteroid is a system of two asteroid-sized bodies bound in mutual orbit. Ida and Dactyl helped prompt broader study of multiple-body asteroid systems.951 Gaspra: 951 Gaspra is a small S-type asteroid visited by the Galileo spacecraft in 1991. Galileo’s earlier asteroid flyby set the stage for its later encounter with Ida.YORP effect: The YORP effect is a torque from uneven thermal radiation that changes a small body's rotation. It is one proposed route by which asteroids can spin up and shed material.Show all 20Linked from 1 pageAsteroid collisionBroader topic: Its irregular, cratered surface preserves evidence of impact history.