We all know that Jupiter played a great role in the Solar System by cleaning up debris and dust from the Solar System, and deflecting asteroids. Saturn also played a similar role. Uranus and Neptune helped Earth by sending water ice-rich comets our way to enrich our planet with water, and now deflect rowdy Kuiper Belt objects.

But, Earth does not seem to play any role in the Solar System. It simply looks as if it is just a honorary guest in the Solar System, just idling in the Solar System. But it must be doing something, like protecting a planet from radiation, or deflecting asteroids away in the Solar System.

What (if any) role did Earth play in the evolution of the solar system?

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    $\begingroup$ You need to be more specific by what you mean by ‘role’. Every planet in the solar system has a ‘role’ in that it gravitationally affects all other planets to some degree or other. $\endgroup$
    – user438383
    Commented Oct 27, 2022 at 8:11
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    $\begingroup$ "We all know that ..." any such statement is bound to be disputed. "But it must be doing something, ...", no, why would it? Stuff just happens according to physics. Whether we assign an arbitrary nomenclature to this as "role" depends entirely on us. There are furthermore factual wrongs and gross oversimplifications in your question, which do not hold to be true. $\endgroup$ Commented Oct 27, 2022 at 8:39
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    $\begingroup$ You seem to be confusing "function" with "purpose". Jupiter does "clear up debris" (to some extent) This is a function of Jupiter. But it is not its "purpose" or "role". Notions of "purpose" suppose some being with agency to give purpose (ie "god") and so questions of the "role" of the Earth are theology, not astronomy. You seem to be personifying the planets, as if they "choose" to protect. $\endgroup$
    – James K
    Commented Oct 27, 2022 at 9:38
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    $\begingroup$ But it must be doing something There is no "must". Basically planets are stuff left over when a star is born. You seem to think everything has a purpose, which just is not how science works. $\endgroup$ Commented Oct 27, 2022 at 10:47
  • $\begingroup$ Well, it "serves" as a parent body for the Moon, for starters. $\endgroup$ Commented Oct 27, 2022 at 11:37

1 Answer 1


All the objects astronomers now call "planets" are major players in the development of our Solar System. By "clearing" or more accurately controlling their orbital neighborhoods, the neighborhood-clearing planets have herded the vast majority of smaller objects into belts and outer zones, and firmly control practically all those which accompany them in their respective orbits (horseshoe-type orbiters, Lagrange-point objects, etc). The main belt of asteroids begins where it is seen to do so precisely because of the cumulative neighborhood-clearing effects of the seemingly small planets out to Mars. One reason "clearing the neighborhood" enters into the definition of a "planet" is the major role it plays in the structure of the Solar System.

In the case of Earth, this neighborhood-clearing role is coupled with that of the Moon. If we were to ignore the "not a satellite" part of the definition of a "planet" and work out the Stern-Levinson parameter of the Moon orbiting the Sun, we would find that the Moon could of itself clear an orbital neighborhood. In the actual setting it plays a secondary role in the clearing of Earth's neighborhood, resulting in Earth's orbital neighborhood being relatively clean even compared with other "planets"; see the Soter planetary discriminant values given by Wikipedia.

  • $\begingroup$ Thanks @jamesk. Every so often Autocorrect goes rogue on me and I add hyphens to words in order to hold it at bay. $\endgroup$ Commented Apr 18, 2023 at 9:59

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