Skip to main content
Select Source:

Roche limit

Roche limit, the closest distance that a celestial body held together only by its own gravity can come to a planet without being pulled apart by the planet's tidal (gravitational) force. This distance depends on the densities of the two bodies and the orbit of the celestial body. Inside the Roche limit, orbiting material will tend to disperse and form rings, while outside the limit, material will tend to amalgamate to form celestial bodies. The French mathematician and astronomer Edouard Roche first enunciated this theoretical limit in 1848.

If a planet and a satellite have identical densities, then the Roche limit is 2.446 times the radius of the planet. Some satellites, both natural and artificial, can orbit within their Roche limits because they are held together by forces other than gravitation. Jupiter's moon Metis and Saturn's moon Pan are examples of natural satellites that survive despite being within their Roche limits—they hold together largely because of their tensile strength. A weaker body, such as a comet, could be broken up when it passes within its Roche limit. For example, comet Shoemaker-Levy 9's decaying orbit around Jupiter passed within its Roche limit in July, 1992, causing it to break into a number of smaller pieces. All known planetary rings are located within the Roche limit, and may be either remnants from the planet's protoplanetary accretion disc that did not amalgamate into satellites or fragments from a body passed within its Roche limit and broke apart.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Roche limit." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 19 Jul. 2018 <http://www.encyclopedia.com>.

"Roche limit." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (July 19, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/roche-limit

"Roche limit." The Columbia Encyclopedia, 6th ed.. . Retrieved July 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/roche-limit

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Roche limit

Roche limit The distance within which the tidal forces exerted by a planet are sufficient to disrupt a satellite or smaller body. For bodies in circular orbits with zero tensile strength and the same mean density as the primary, the Roche limit is 2.46 × (primary-body radius). In the case of the Earth—Moon system, the critical distance is 2.89 Earth radii (18 400 km).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Roche limit." A Dictionary of Earth Sciences. . Encyclopedia.com. 19 Jul. 2018 <http://www.encyclopedia.com>.

"Roche limit." A Dictionary of Earth Sciences. . Encyclopedia.com. (July 19, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/roche-limit

"Roche limit." A Dictionary of Earth Sciences. . Retrieved July 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/roche-limit

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.