Featured Research: Forming Binary Asteroids

In 1993, NASA's Galileo spacecraft discovered Ida, the first known asteroid with its own moon (Dactyl). Now, Assistant Professor Derek Richardson and his students Zoe Leinhardt and Kevin Walsh are studying how a process known as tidal disruption could explain how such binaries form among the near-Earth asteroid population. Tidal disruption means that the gravitational force felt by an asteroid which passes by the Earth overcomes the cohesiveness of the asteroid, pulling it apart. The pieces are then available to become tiny moon(s) of what's left of the asteroid. Richardson and his students find that a wide variety of outcomes are possible, from small to large companions (moons), circular to elliptical orbits, and spheroidal to ellipsoidal shapes, depending on the close-approach distance and encounter speed of the progenitor with a terrestrial planet like the Earth. A similar process created the spectacular Comet Shoemaker-Levy 9 fragment train.

Click on the snapshot above to see an MPEG movie (1.1 MB) showing the formation of an asteroid binary by tidal disruption. In the movie, the camera is fixed above the asteroid as it swings by the Earth (the planet passes by on the left but cannot be seen in this view). The particles that make up the asteroid have been raytraced to make the bodies look more "realistic." For more information about these experiments, see the researchers' article(200K PDF) presented at the Asteroids, Comets, Meteors 2002 Conference.

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