Roche limit

astronomical concept

The Roche limit (pronounced /ˈroʊʃ/), sometimes referred to as the Roche radius, is the distance within which a celestial body, held together only by its own gravity, will disintegrate due to a second celestial body's tidal forces exceeding the first body's gravitational self-attraction.[1] Inside the Roche limit, orbiting material will tend to disperse and form planetary rings, while outside the limit, material will tend to coalesce. The term is named after Édouard Roche, the French astronomer who first calculated this theoretical limit in 1848.[2]

Consider an orbiting mass of fluid held together by gravity, here viewed from above the orbital plane. Far from the Roche limit 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 planetary ring


  1. Eric W. Weisstein (2007). "Eric Weisstein's World of Physics - Roche Limit". Retrieved September 5, 2007. Check date values in: |accessdate= and |year= (help)
  2. NASA. "What is the Roche limit?". NASA - JPL. Archived from the original on 2013-02-04. Retrieved September 5, 2007. Check date values in: |accessdate= (help)


  • Édouard Roche: La figure d'une masse fluide soumise à l'attraction d'un point éloigné, Acad. des sciences de Montpellier, Vol. 1 (1847–50) p. 243

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