Roche limit

The Roche limit (pronounced /ˈroʊʃ/), or Roche radius, is a planetary distance.

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

Inside the Roche limit, orbiting material will form planetary rings. Outside the limit, material sticks together and forms satellites.

The term is named after Édouard Roche, the French astronomer who first stated it in 1848.

Sources

• 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

Other websites

• Detailed derivation of formulae for calculating the Roche limit
• Discussion of the Roche Limit Archived 2007-08-26 at the Wayback Machine