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In popular science fiction, we see habitable Earth-like planets with visible, Saturn-like rings.

In reality, such rings exist only on gas giants, a category where we can find Saturn.

Is it really possible for a planet similar in gravity to Earth to have the kind of gravity needed to create these rings? If no, then what kind of changes would I do to make sure Earth does have them?

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    $\begingroup$ At the risk of self-promotion, my answer here talks about this. $\endgroup$ – HDE 226868 Oct 16 '15 at 23:07
  • $\begingroup$ I know that we had a very similar question early during the site's beta period, but I can't seem to find it. One answer even had a picture showing what it would look like from the ground... $\endgroup$ – a CVn Oct 17 '15 at 19:05
  • $\begingroup$ @MichaelKjörling are you thinking of this question? It asks what it would look like rather than about how to do it. $\endgroup$ – Monica Cellio Oct 18 '15 at 2:51
  • $\begingroup$ I'm asking if it's possible for someone the size and gravity of Earth to have Saturn-like rings, as often portrayed in science-fiction. $\endgroup$ – JohnWDailey Oct 18 '15 at 3:07
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    $\begingroup$ It think "what it takes" is called gravity. $\endgroup$ – Serban Tanasa Jun 17 '16 at 13:53
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Yes, Earth is large enough to have rings. What you need would be an object orbiting close to the planet like a small moon. It needs to be inside the Roche limit, where the object will start to disintegrate because of the tidal forces.

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    $\begingroup$ As it turns out, we have an object that would make some nice rings. Now only how to get it within the Roche Limit? $\endgroup$ – PyRulez Oct 17 '15 at 1:26
  • $\begingroup$ @PyRulez How about Earth with planetary ring? $\endgroup$ – a CVn Oct 17 '15 at 19:04
  • $\begingroup$ @PyRulez You could use a large rocket/engine/whatever to push the celestial body where you want it. $\endgroup$ – Vincent Oct 17 '15 at 19:21
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We kind of already do:

enter image description here

This is a false-scale image of all objects in orbit around the Earth that NASA/RSA/EASA jointly monitor. You can clearly see the outer ring of GEO objects. Most of these objects are manmade, and most of those are space junk; decommissioned satellites and their debris, pieces of launch vehicles we had to accelerate fast enough to get into a stable orbit, etc. There are thousands more manmade pieces of debris that NASA doesn't keep an eye on because they're too small to pose a re-entry hazard and aren't in a conflicting orbit with any valuable satellites. There was, at one point, an image from a survey probe that caught a beautiful "goodbye" picture of Earth with the sun perfectly aligned to glint off the debris ring around Earth, but I can't find it in the midst of all the "artist's impressions" and enhanced images.

In addition to debris, there's space dust and meteoroids that have been drawn into a stable orbit around Earth, too small to track, but definitely still a hazard; this is what one of those micrometeorites did to the Challenger on STS-7:

enter image description here

As far as why we don't have more, it's mainly chance. A long-term stable orbit around a planet of Earth's size is a fairly tricky thing to achieve, especially without being able to make adjustments. The rings around the gas giants are much more prominent for three reasons:

  • They're more massive, so as they formed, they carved wider swaths out of the accretion disk as they "cleared the neighborhood" of their orbit. In addition to its size (95Me) and its rings, Saturn has 13 objects large and round enough to call "moons" (at least 50km diameter), plus 40 additional named orbiting bodies and another 9 objects with a confirmed size and orbit.
  • They're further out than Earth, so they get the first shot at capturing "new" stuff that de-orbits from the Kuiper belt and Oort cloud out around and beyond Pluto.
  • Because of the relative importance of the mass term and the distance term in gravitational force equations, more massive objects have a wider range of stable orbits, thus random object incursion doesn't have to be quite so precise as it would around Earth.

In addition, what you're seeing around the gas giants is survivor bias; the gas giants, being, well, gas and giants, are much more tolerant of outright impacts, so we don't really see their effects unless we happen to be watching (like when the remains of Shumacher-Levy 9 hit Jupiter). The earth, in its first few million years of existence as a ball of cooling magma, was nearly destroyed by a mass that would become the moon. This chance encounter turned out to be advantageous for the planet, as it gained a sizable shield which has protected the planet from countless impacts over the years by taking the hits itself.

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  • $\begingroup$ The problem is, these rings aren't visible. $\endgroup$ – JohnWDailey Oct 17 '15 at 0:33
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    $\begingroup$ I very much want to upvote this beautiful answer, but it doesn't answer the question from what I interpret the intent (actual rings like we see around Saturn). If you could simply add: "yes, Earth can, but only if xyz happens," or "no, Earth cannot, because of xyz reasons," then I would vote this as the best answer. I think the answer is somewhere in here, but it is not explicit. $\endgroup$ – Mikey Apr 15 '17 at 16:25
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Earth DID have a ring! BUT, it slowly collapsed in on itself by the force of its own gravity.

4.527–4.533 Billion years ago Theia, a planet with a size similar to Mars, smashed into Earth, and the remains collected in orbit around earth. That is why Luna is comprised partially of mater originating from Earth's crust. (Some people used to call Theia "Orpheus")

Theia originally orbited around Earth at the L4-L5 points. As it gained mass it was slowly knocked loose from orbit by Venus, and caused it to strike Earth, possibly merging the two planetary cores, which is why Earth's core is much larger than the cores of similarly sized planets.

In around a century (less than two) gravity collected all the larger portions together into Luna. Within the next Million years, the crust had formed. Over the next 300 million years (3.9B–4.1B) meteor storms and comets ripped the surface back apart, temporarily creating ANOTHER small ring. It settled back when the "weather" calmed down again, until about 108 million years ago when the last great asteroid impact formed the Tycho crater.

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  • $\begingroup$ Did this prehistoric ring resemble Saturn's in any way? $\endgroup$ – JohnWDailey Oct 17 '15 at 3:44
  • $\begingroup$ The last great asteroid impact was 65 million years ago and scientists speculate the asteroid came from the asteroid belt (between Mars and Jupiter). Debris resulting from Theia-Earth collision would be more likely to fall on Earth than Moon as Earth has ~6 times stronger gravity. $\endgroup$ – Youstay Igo Oct 17 '15 at 7:56
  • $\begingroup$ possibly, but on a MUCH smaller scale. Saturn has the ability to gravatationally hold MUCH MORE debris in orbit than Earth does. $\endgroup$ – Ronk Apr 29 '16 at 8:20
  • $\begingroup$ The post-impact situation did not resemble rings. It would be classified as an extended atmosphere, as detailed in a presentation I saw in the SETI colloquium series. $\endgroup$ – JDługosz Jun 16 '16 at 16:40
  • $\begingroup$ Was that pasted from another text file? I wonder if you need to cite a source, or you just edit in notepad first. $\endgroup$ – JDługosz Jun 16 '16 at 16:41
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Solid bodies disintegrate after reaching the Roche Limit. However, Earth´s Roche Limit is a little bit inside the atmosphere so any body that is destroyed by tidal forces inside that limit will also fall by loss of potential gravitational energy because of any interaction between air particles and molecules, this is why Earth doesn't have rings. If we have a smaller, less massive and thinner atmosphere it could be possible for Earth to have rings.

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