also: ロッシュげんかい
noun
Roche limit
Technical term in astronomy: the closest distance a celestial body held together only by gravity can approach a planet without being torn apart by tidal forces.
土星の環はロシュ限界の内側にあるため、衛星が形成されなかったと考えられている。
Saturn's rings are thought to lie inside the Roche limit, which prevented a moon from forming.
From French 'Roche' (after Édouard Roche) + 限界 (limit).