Roche limit

This article is about the orbit within which particles might form rings or objects on a stable orbit might disintegrate into rings. For the limits at which an orbiting object will be captured, see Roche lobe. For the gravitational sphere of influence of one astronomical body in the face of perturbations from another heavier body around which it orbits, see Roche sphere.
A celestial body (yellow) is orbited by a mass of fluid (blue) held together by gravity, here viewed from above the orbital plane. Far from the Roche limit (white line), the mass is practically spherical.
Closer to the Roche limit, the body is deformed by tidal forces.
Within the Roche limit, the mass's own gravity can no longer withstand the tidal forces, and the body disintegrates.
Particles closer to the primary move more quickly than particles farther away, as represented by the red arrows.
The varying orbital speed of the material eventually causes it to form a ring.

In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal forces exceed the second body's self-gravitation.[1] Inside the Roche limit, orbiting material disperses and forms rings, whereas outside the limit, material tends to coalesce. The Roche radius depends on the radius of the first body and on the ratio of the bodies' densities.

The term is named after Édouard Roche (French: [ʁɔʃ], English: /rɒʃ/ ROSH), the French astronomer who first calculated this theoretical limit in 1848.[2]

  1. ^ Weisstein, Eric W. (2007). "Eric Weisstein's World of Physics – Roche Limit". scienceworld.wolfram.com. Retrieved September 5, 2007.
  2. ^ NASA. "What is the Roche limit?". NASA – JPL. Archived from the original on April 23, 2009. Retrieved September 5, 2007.