In the end stages of planet formation, a planet will have cleared the neighbourhood of its own orbital zone, meaning it has become gravitationally dominant, and there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence. The current definition of a planet adopted by the International Astronomical Union (IAU) only includes those bodies which have "cleared the neighbourhood of its orbit"^[1]. A large body which meets the other criteria for a planet but has not cleared its neighbourhood is classified as a dwarf planet. This includes Pluto, which shares its orbital neighbourhood with Kuiper Belt Objects such as the plutinos. The IAU's definition does not attach specific numbers or equations to this term, however the extent to which all the planets have cleared their neighbourhoods is much greater, by any measure, than that of any dwarf planet or any candidate for dwarf planet known so far. The accretion theory, in astrophysics, is a scientific theory of the formation of our Solar system. ... The eight planets and three dwarf planets of the Solar System. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ... Photograph of the planet Neptune and its moon Triton, taken by Voyager 2 as it entered the outer solar system. ... Logo of the IAU The International Astronomical Union (French: Union astronomique internationale) unites national astronomical societies from around the world. ... Artists impression of Pluto (background) and Charon (foreground). ... Adjectives: Plutonian Atmosphere Surface pressure: 0. ... The Kuiper belt (KYE per) is an area of the solar system extending from within the orbit of Neptune (at 30 AU) to 50 AU from the sun, at inclinations consistent with the ecliptic. ... In astronomy, a plutino is a trans-Neptunian object that has a 3:2 orbital resonance with Neptune. ...

The phrase may be derived from a paper presented to the general assembly of the IAU in 2000 by Alan Stern and Harold Levison. The authors used several similar phrases as they developed a theoretical basis for determining if an object orbiting a star is likely to "clear its neighboring region" of planetesimals, based on the object's mass and its orbital period.^[2] 2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ... This page may meet Wikipedias criteria for speedy deletion. ... Harold F. Hal Levison is a planetary scientist specializing in planetary dynamics. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ...

Clearly distinguishing "planets" from "dwarf planets" and other minor planets had become necessary because the IAU had adopted different rules for naming newly discovered major planets and newly discovered minor planets, without establishing a basis for telling them apart. The naming process for Eris stalled after the announcement of its discovery in 2005, pending clarification of this first step. Minor planets, or asteroids or planetoids, are minor celestial bodies of the Solar system orbiting the Sun (mostly Small solar system bodies) that are smaller than major planets, but larger than meteoroids (commonly defined as being 10 meters across or less[1]), and that are not comets. ... Absolute magnitude: −1. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...

Details

The phrase refers to an orbiting body (a planet or protoplanet) "sweeping out" its orbital region over time, by gravitationally interacting with smaller bodies nearby. Over many orbital cycles, a large body will tend to cause small bodies either to accrete with it, or to be disturbed to another orbit. As a consequence it does not then share its orbital region with other bodies of significant size, except for its own satellites, or other bodies governed by its own gravitational influence. This latter restriction excludes objects whose orbits may cross but which will never collide with each other due to orbital resonance, such as Jupiter and the Trojan asteroids, Earth and 3753 Cruithne or Neptune and the plutinos.^[2] In cosmogony, a protoplanet is a quasi-planetoid which is slightly larger than a planetesimal and orbits within a solar nebulas protoplanetary discs. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... “Gravity” redirects here. ... ... In astrophysics, the term accretion is used for at least two distinct processes. ... An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ... In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Image of the Trojan asteroids in front of and behind Jupiter along its orbital path. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... 3753 Cruithne (pronounced ) is an asteroid in orbit around the Sun. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... In astronomy, a plutino is a Pluto-like object, insofar as it has the same relative orbit as Pluto. ...

Steven Soter of the Department of Astrophysics, American Museum of Natural History, has written that "A heliocentric body with Λ > 1 [viz., a planet] has cleared a substantial fraction of small bodies out of its orbital neighborhood."^[3] Λ (Lambda) is a parameter proposed by Stern and Levison^[2] that measures the extent to which a body scatters smaller masses out of its orbital zone over a long period of time. Mathematically Λ is defined as Steven Soter is an astronomer who argued for a distinction between dwarf planets and the other eight planets based on their inability to clear the neighborhood around their orbits. This article belongs in one or more categories. ... This article or section does not cite its references or sources. ... Look up Λ, λ in Wiktionary, the free dictionary. ...

where k is approximately constant and M and P are the scattering body's mass and orbital period, respectively. Two bodies are defined to share an orbital zone if their orbits cross a common radial distance from the primary, and their non-resonant periods differ by less than an order of magnitude. The order-of-magnitude similarity in period requirement excludes comets from the calculation, but the combined mass of the comets turn out to be negligible compared to the other small solar system bodies anyway so their inclusion would have little impact on the results. Stern and Levison found a gap of five orders of magnitude in Λ between the smallest terrestrial planets and the largest asteroids and Kuiper Belt Objects (KBOs). Artists rendering of the Kuiper Belt and hypothetical more distant Oort cloud. ...

Soter went on to propose a parameter he called the "planetary discriminant", designated with the symbol µ (mu) , that represents an experimental measure of the actual degree of cleanliness of the orbital zone. µ is calculated by dividing the mass of the candidate body by the total mass of the other objects that share its orbital zone. Look up Îœ, μ in Wiktionary, the free dictionary. ...

The calculated parameters for major solar system bodies are:^[3]

*Λ/Λ_E = M²/P, in Earth masses squared per year.
**µ = M/m, where M is the mass of the body, and m is the aggregate mass of all the other bodies that share its orbital zone. This article is about the planet. ... (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9. ... Earth, also known as the Earth or Terra, is the third planet outward from the Sun. ... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... Spectral type: G[8] Absolute magnitude: 3. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... Atmospheric characteristics Atmospheric pressure 120 kPa Hydrogen 83% Helium 15% Methane 1. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... Adjectives: Plutonian Atmosphere Surface pressure: 0. ... Absolute magnitude: −1. ...

Controversy

Orbits of celestial bodies in the Kuiper Belt with approximate distances and inclination. Objects marked with red are in orbital resonances with Neptune, with Pluto (the largest red circle) located in the "spike" of plutinos at the 2:3 resonance

Stern, currently leading the NASA New Horizons mission to Pluto, objects to the reclassification of Pluto on the basis that—like Pluto—Earth, Mars, Jupiter and Neptune have not cleared their orbital neighbourhoods either. Earth co-orbits with 10,000 near-Earth asteroids, and Jupiter has 100,000 Trojan asteroids in its orbital path. "If Neptune had cleared its zone, Pluto wouldn't be there," he now says.^[4] Image File history File links TheKuiperBelt_75AU_All. ... Image File history File links TheKuiperBelt_75AU_All. ... The National Aeronautics and Space Administration (NASA) is an agency of the United States federal government, responsible for the nations public space program. ... New Horizons is a robotic spacecraft mission conducted by NASA. It is expected to be the first spacecraft to fly by and study the dwarf planet Pluto and its moons, Charon, Nix and Hydra. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earths orbit. ...

However, in 2000 Stern himself wrote, "we define an überplanet as a planetary body in orbit about a star that is dynamically important enough to have cleared its neighboring planetesimals ..." and a few paragraphs later, "From a dynamical standpoint, our solar system clearly contains 8 überplanets"—including Earth, Mars, Jupiter, and Neptune.^[2] Most planetary scientists understand "clearing the neighborhood" to refer to an object being the dominant mass in its vicinity, for instance Earth being many times more massive than all of the NEA's combined, and Neptune "dwarfing" Pluto and the rest of the KBO's.^[3] Artists rendering of the Kuiper Belt and hypothetical more distant Oort cloud. ...

Stern and Levison's paper shows that it's possible to estimate whether an object is likely to dominate its neighborhood given only the object's mass and orbital period, known values even for extrasolar planets. In any case, the recent IAU definition specifically limits itself only to objects orbiting the Sun.^[1]

See also

• Planet
• List of solar system objects by planetary discriminant

The eight planets and three dwarf planets of the Solar System. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

References

August 24 is the 236th day of the year in the Gregorian calendar (237th in leap years), with 129 days remaining. ... For the Manfred Mann album, see 2006 (album). ... For the Manfred Mann album, see 2006 (album). ... August 26 is the 238th day of the year (239th in leap years) in the Gregorian calendar. ... PDF is an abbreviation with several meanings: Portable Document Format Post-doctoral fellowship Probability density function There also is an electronic design automation company named PDF Solutions. ... August 7 is the 219th day of the year (220th in leap years) in the Gregorian calendar. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... 2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ... PDF is an abbreviation with several meanings: Portable Document Format Post-doctoral fellowship Probability density function There also is an electronic design automation company named PDF Solutions. ... For the Manfred Mann album, see 2006 (album). ... August 24 is the 236th day of the year in the Gregorian calendar (237th in leap years), with 129 days remaining. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... August 25 is the 237th day of the year in the Gregorian calendar (238th in leap years), with 128 days remaining. ... For the Manfred Mann album, see 2006 (album). ... For the Manfred Mann album, see 2006 (album). ... September 3 is the 246th day of the year (247th in leap years) in the Gregorian calendar. ...

External links

• al-Jazeera: Pluto central in battle of the planets (Associated Press) Thursday 24 August 2006, 10:48 Makka Time, 7:48 GMT
• Ottawa Citizen: The case against Pluto (P. Surdas Mohit) Thursday, August 24, 2006