<p>Earth, Mars, Jupiter and Neptune have &quot;cleared their orbits&quot; in the following technical sense:  There are no objects that are co-orbital, of comparable mass, not in a orbit that is controlled or resonant with the planet.</p>
<p>So the Earth shares it's orbit with the Moon, but the moon's orbit around the sun is dominated by the Earth.  Jupiter shares its orbits with it's moons and its Trojans.  But the orbits of the Trojans are maintained by Jupiter's gravity.  Neptune shares its orbit with Pluto, but the orbit of Pluto is maintainted in a 3:2 resonance with Neptune. It is the much larger mass of Neptune that maintains this resonance, not the mass of Pluto. By contrast, Pluto has not &quot;cleared its orbit&quot;  There are numerous other bodies of comparable size or largder that share a similar orbit to Pluto.  Likewise Ceres has not cleared it's orbit.  It shares its orbit with other asteroids which are not held in resonant orbit.</p>
<p>Therefore, Earth, Mars, Neptune and Jupiter are called &quot;planets&quot;.</p>

CC BY-SA 4.0
2020-08-17T21:00:15.230Z
I just wanted to add that in addition to the good points you make above there are also the L4 & L5 Lagrange points ... but those points exist due to the gravity of the planet controlling them.

Humorously, a *much* older definition of planet was that it had to be a heavenly body which moved.  This meant the Sun and Moon *were* planets and Earth was *not* a planet.
Tim Campbell
CC BY-SA 4.0
2020-08-17T21:01:12.743Z
L4 and L5 mean "trojans" (and "greeks")
James K
CC BY-SA 4.0
2020-08-18T11:28:35.797Z
Now explain what a 3:2 resonance is?
user2617804
CC BY-SA 4.0
2020-08-18T13:38:18.363Z
@user2617804: In this case it means that Neptune orbits the Sun three times for every two times Pluto orbits the Sun.
David Hammen
CC BY-SA 4.0
2020-08-17T15:27:44.003Z
2020-08-17T19:33:54.937Z
2020-08-17T19:33:54.937Z
James K
<blockquote>
<p>Just like every astronomer they give zero evidence or real explanation for clearing their orbits.</p>
</blockquote>
<p>There are three very specific and quantitative metrics regarding <a href="https://en.wikipedia.org/wiki/Clearing_the_neighbourhood" rel="nofollow noreferrer">clearing the neighborhood</a>. All three show a multiple order of magnitude gap between Mars (the planet with the smallest metric, on all three scales) and Ceres or Pluto (the  dwarf planets with the largest metric; which is largest depends on the metric).</p>
<p>One of these metrics was proposed six years before the vote to demote Pluto from planethood by S. Alan Stern, one of the most vocal critics of that demotion. <strong>It was Stern's own metric that led to Pluto's demise.</strong> Whenever there is a six order of magnitude difference in a metric used for classification, that metric (a) is a very good metric, and (b) almost certainly shows something real. The distinction between the eight planets and the smaller solar system bodies is real distinction. Stern knew that; the only difference between Stern's 2000 paper and the IAU vote in 2006 was that Stern wanted to label the objects on opposite sides of that huge gap as uberplanets and unterplanets. The IAU decided to use planets and dwarf planets instead. Despite the &quot;dwarf&quot; qualifier, dwarf planets are not planets.</p>
<p>The distinction is real, so what has happened to make that distinction real? The answer is simple: Each of the planets has cleared the neighborhood of their orbits to such a huge extent that each those things we call &quot;planets&quot; is far and away the most massive object in the vicinity of those objects' orbits. There are multiple ways that a planet can &quot;clear its neighborhood.&quot;</p>
<p>They can collide with lesser objects, possibly resulting in a moon (e.g., the Earth and the Moon). They can expel objects from the solar system (e.g., a proposed fifth giant planet that was expelled by the four remaining giant planets, along with numerous comets and asteroids that have been expelled). They can capture lesser objects as moons (e.g., the myriad outer moons of the giant planets, and possibly the moons of Mars). They can effectively capture lesser objects as co-orbiting bodies (e.g., Jupiter's trojans in pseudo orbits about Jupiter's L4 and L5 points, various objects that co-orbit the Earth in horseshoe orbits or tadpole orbits). In a sense, Pluto is a co-orbiting object of Neptune. Neptune has forced Pluto, along with several other objects, to be in a 3:2 orbital resonance with Neptune.</p>
<p>To be deemed to be a &quot;planet,&quot; an object has to pass two other qualification tests: Does the object orbit the Sun, and is it round? There is no reason for the &quot;is it round&quot; test. Any object massive enough to have cleared its neighborhood will almost certainly be round. The &quot;does it orbit the Sun&quot; test is even worse, in a way.</p>
<p>The &quot;does it orbit the Sun&quot; test means that there are only eight planets in the entire universe. The large and growing number of exoplanets are not planets simply because they do not orbit the Sun. Moreover, scientists have only directly observed a small number of exoplanets, none of which have been observed with enough resolution to determine whether they pass the &quot;is it round&quot; test.</p>
<p>Instead of the &quot;clearing the neighborhood&quot; test, which is a very good one, what the IAU should do is to get rid of the &quot;is it round&quot; test and replace the &quot;does it orbit the Sun&quot; test with a &quot;does it orbit a star&quot; test. There is no quantitative metric for &quot;roundness&quot;, and if there was it would be very arbitrary. Objects 1000 km in diameter tend to be &quot;roundish&quot;, while objects less than 100 km in diameter tend to be lumpy. In between, it's a bit fuzzy if objects are roundish or lumpy. An object capable of clearing its neighborhood, in any star system, will almost certainly be more well over 1000 km across.</p>

CC BY-SA 4.0
2020-08-22T08:33:14.740Z
Both answers have their strengths but add more terminology that is poorly expressed and some details are vague. The David Hammen answer has a lot of extraneous content. Wikipedia doesn't well describe what an orbital zone is.
user2617804
CC BY-SA 4.0
2021-03-23T01:10:28.373Z
There are good statistical measures of roundness. They wouldn't be more arbitrary than Stern-Levinson's k parameter. Jupiter and Mars differ in mass by 4 orders of magnitude. We might consider removing Mars and Mercury's planet status next.
tobuslieven
CC BY-SA 4.0
2021-03-23T02:15:13.710Z
@tobuslieven Name one good statistical measure of roundness such that solar system objects can be clearly and objectively distinguished as "round" or "not round" and that has a huge unfilled gap between "round" and "not round". You won't find it; such a measure does not and cannot exist. On the other hand, whenever one finds (or an AI finds) a multiple order of magnitude empty gap in some metric there's probably something very real going on. The gap between Jupiter and Mars (in the case of the  Stern-Levinson is not an empty gap. There are six other planetary objects that fill that gap.
David Hammen
CC BY-SA 4.0
2021-03-24T07:13:45.383Z
Stern-Levinson is unclear and subjective. But you seem to be defending it.
tobuslieven
CC BY-SA 4.0
2023-09-04T20:00:45.777Z
Not "Pluto's demise" at all. What happened to Pluto is really part of a trend where things are meriting astronomical study even when they're not "planets".
Oscar Lanzi
CC BY-SA 4.0
2020-08-18T13:36:04.160Z
2020-08-18T13:36:04.160Z
David Hammen
<p>According National Geographic's Space Encyclopedia (p68, column 3) written and illustrated by David A Aguilar</p>
<blockquote>
<p>Pluto has not cleared its orbit of space debris but neither have Earth, Mars, Jupiter and Neptune.</p>
</blockquote>
<p>Just like every astronomer they give zero evidence or real explanation for clearing their orbits. NASA just says</p>
<blockquote>
<p>An orbit is a regular, repeating path that one object in space takes around another one</p>
</blockquote>
<p>This is pretty limiting and every planet must clear its orbit otherwise it would smash into anything in its orbit.
Would anyone like to explain in precise terms what is &quot;around an orbit&quot; and &quot;space debris&quot; and what is clearing of such space debris in respect to Earth, Mars, Jupiter and Neptune- that they have or not done so?</p>

CC BY-SA 4.0
2020-08-17T15:10:04.030Z
"Just like every astronomer they give zero evidence or real explanation", and you expect to get an explanation here by who exactly? Computer scientists?
AtmosphericPrisonEscape
CC BY-SA 4.0
2020-08-18T01:18:13.943Z
@antispinwards - It's never-ending, unfortunately.
David Hammen
CC BY-SA 4.0
2020-08-18T10:55:58.720Z
Re *According National Geographic's S@ace Encyclopedia, Earth, Mars, Jupiter and Neptune have not cleared their orbits*: Citation needed.
David Hammen
CC BY-SA 4.0
2020-08-18T15:12:13.400Z
That's a quote rather than a link. That said, David Aguilar is not on unbiased observer. He left the Harvard-Smithsonian Center for Astrophysics to join NASAs New Horizons special media team on the Pluto flyby mission. The people who worked on New Horizons did not like the IAU's demotion of Pluto to "dwarf planet" category and have intentionally spread misinformation regarding that demotion. This appears to be part and parcel of that disinformation campaign.
David Hammen
CC BY-SA 4.0
2020-08-22T08:35:32.823Z
Unbiased observer in astronomy? There is no unbiased observer in any science. He didn't provide any data so he couldn't corrupt any data.
user2617804
<orbit><planet>
Have Earth, Mars and Jupiter and Neptune not cleared their orbits of space debris?
user2617804
# Have Earth, Mars and Jupiter and Neptune not cleared their orbits of space debris?

(Asked by: username_0 on 2020-08-17)

According National Geographic's Space Encyclopedia (p68, column 3) written and illustrated by David A Aguilar

> Pluto has not cleared its orbit of space debris but neither have Earth, Mars, Jupiter and Neptune.

Just like every astronomer they give zero evidence or real explanation for clearing their orbits. NASA just says

> An orbit is a regular, repeating path that one object in space takes around another one

This is pretty limiting and every planet must clear its orbit otherwise it would smash into anything in its orbit.
Would anyone like to explain in precise terms what is "around an orbit" and "space debris" and what is clearing of such space debris in respect to Earth, Mars, Jupiter and Neptune- that they have or not done so?

**Tags:** orbit, planet

> **Comments:**
> **username_1**: "Just like every astronomer they give zero evidence or real explanation", and you expect to get an explanation here by who exactly? Computer scientists?  
> **username_2**: @antispinwards - It's never-ending, unfortunately.  
> **username_2**: Re *According National Geographic's S@ace Encyclopedia, Earth, Mars, Jupiter and Neptune have not cleared their orbits*: Citation needed.  
> **username_2**: That's a quote rather than a link. That said, David Aguilar is not on unbiased observer. He left the Harvard-Smithsonian Center for Astrophysics to join NASAs New Horizons special media team on the Pluto flyby mission. The people who worked on New Horizons did not like the IAU's demotion of Pluto to "dwarf planet" category and have intentionally spread misinformation regarding that demotion. This appears to be part and parcel of that disinformation campaign.  
> **username_0**: Unbiased observer in astronomy? There is no unbiased observer in any science. He didn't provide any data so he couldn't corrupt any data.  

---

## 2 answers

### Answer by username_3 on 2020-08-17. Score: 10

Earth, Mars, Jupiter and Neptune have "cleared their orbits" in the following technical sense: There are no objects that are co-orbital, of comparable mass, not in a orbit that is controlled or resonant with the planet.

So the Earth shares it's orbit with the Moon, but the moon's orbit around the sun is dominated by the Earth. Jupiter shares its orbits with it's moons and its Trojans. But the orbits of the Trojans are maintained by Jupiter's gravity. Neptune shares its orbit with Pluto, but the orbit of Pluto is maintainted in a 3:2 resonance with Neptune. It is the much larger mass of Neptune that maintains this resonance, not the mass of Pluto. By contrast, Pluto has not "cleared its orbit" There are numerous other bodies of comparable size or largder that share a similar orbit to Pluto. Likewise Ceres has not cleared it's orbit. It shares its orbit with other asteroids which are not held in resonant orbit.

Therefore, Earth, Mars, Neptune and Jupiter are called "planets".

> **Comments:**
> **username_4**: I just wanted to add that in addition to the good points you make above there are also the L4 & L5 Lagrange points ... but those points exist due to the gravity of the planet controlling them.  Humorously, a *much* older definition of planet was that it had to be a heavenly body which moved.  This meant the Sun and Moon *were* planets and Earth was *not* a planet.  
> **username_3**: L4 and L5 mean "trojans" (and "greeks")  
> **username_0**: Now explain what a 3:2 resonance is?  
> **username_2**: @username_0: In this case it means that Neptune orbits the Sun three times for every two times Pluto orbits the Sun.  

---

### Answer by username_2 on 2020-08-18. Score: 4

> Just like every astronomer they give zero evidence or real explanation for clearing their orbits.

There are three very specific and quantitative metrics regarding [clearing the neighborhood](https://en.wikipedia.org/wiki/Clearing_the_neighbourhood). All three show a multiple order of magnitude gap between Mars (the planet with the smallest metric, on all three scales) and Ceres or Pluto (the dwarf planets with the largest metric; which is largest depends on the metric).

One of these metrics was proposed six years before the vote to demote Pluto from planethood by S. Alan Stern, one of the most vocal critics of that demotion. **It was Stern's own metric that led to Pluto's demise.** Whenever there is a six order of magnitude difference in a metric used for classification, that metric (a) is a very good metric, and (b) almost certainly shows something real. The distinction between the eight planets and the smaller solar system bodies is real distinction. Stern knew that; the only difference between Stern's 2000 paper and the IAU vote in 2006 was that Stern wanted to label the objects on opposite sides of that huge gap as uberplanets and unterplanets. The IAU decided to use planets and dwarf planets instead. Despite the "dwarf" qualifier, dwarf planets are not planets.

The distinction is real, so what has happened to make that distinction real? The answer is simple: Each of the planets has cleared the neighborhood of their orbits to such a huge extent that each those things we call "planets" is far and away the most massive object in the vicinity of those objects' orbits. There are multiple ways that a planet can "clear its neighborhood."

They can collide with lesser objects, possibly resulting in a moon (e.g., the Earth and the Moon). They can expel objects from the solar system (e.g., a proposed fifth giant planet that was expelled by the four remaining giant planets, along with numerous comets and asteroids that have been expelled). They can capture lesser objects as moons (e.g., the myriad outer moons of the giant planets, and possibly the moons of Mars). They can effectively capture lesser objects as co-orbiting bodies (e.g., Jupiter's trojans in pseudo orbits about Jupiter's L4 and L5 points, various objects that co-orbit the Earth in horseshoe orbits or tadpole orbits). In a sense, Pluto is a co-orbiting object of Neptune. Neptune has forced Pluto, along with several other objects, to be in a 3:2 orbital resonance with Neptune.

To be deemed to be a "planet," an object has to pass two other qualification tests: Does the object orbit the Sun, and is it round? There is no reason for the "is it round" test. Any object massive enough to have cleared its neighborhood will almost certainly be round. The "does it orbit the Sun" test is even worse, in a way.

The "does it orbit the Sun" test means that there are only eight planets in the entire universe. The large and growing number of exoplanets are not planets simply because they do not orbit the Sun. Moreover, scientists have only directly observed a small number of exoplanets, none of which have been observed with enough resolution to determine whether they pass the "is it round" test.

Instead of the "clearing the neighborhood" test, which is a very good one, what the IAU should do is to get rid of the "is it round" test and replace the "does it orbit the Sun" test with a "does it orbit a star" test. There is no quantitative metric for "roundness", and if there was it would be very arbitrary. Objects 1000 km in diameter tend to be "roundish", while objects less than 100 km in diameter tend to be lumpy. In between, it's a bit fuzzy if objects are roundish or lumpy. An object capable of clearing its neighborhood, in any star system, will almost certainly be more well over 1000 km across.

> **Comments:**
> **username_0**: Both answers have their strengths but add more terminology that is poorly expressed and some details are vague. The username_2 answer has a lot of extraneous content. Wikipedia doesn't well describe what an orbital zone is.  
> **username_5**: There are good statistical measures of roundness. They wouldn't be more arbitrary than Stern-Levinson's k parameter. Jupiter and Mars differ in mass by 4 orders of magnitude. We might consider removing Mars and Mercury's planet status next.  
> **username_2**: @username_5 Name one good statistical measure of roundness such that solar system objects can be clearly and objectively distinguished as "round" or "not round" and that has a huge unfilled gap between "round" and "not round". You won't find it; such a measure does not and cannot exist. On the other hand, whenever one finds (or an AI finds) a multiple order of magnitude empty gap in some metric there's probably something very real going on. The gap between Jupiter and Mars (in the case of the  Stern-Levinson is not an empty gap. There are six other planetary objects that fill that gap.  
> **username_5**: Stern-Levinson is unclear and subjective. But you seem to be defending it.  
> **username_6**: Not "Pluto's demise" at all. What happened to Pluto is really part of a trend where things are meriting astronomical study even when they're not "planets".  

---

