It may be surprising to know that all four giants in our solar system have rings orbiting around them. Yet only Saturn has a system of rings visible to the naked eye. Why is that? What's so different about Saturn in comparison to Jupiter, Uranus and Neptune that makes it the only planet to have a visible ring system?
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2 Answers
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By "visible to the naked eye", I take it you mean "visible from Earth with a small telescope".
Saturn's rings are largely water ice, and so they reflect more sunlight back to us.
Jupiter's rings, have lower proportions of ice, and lots of smaller dust particles that tend to scatter light forward rather than back to us.
The ring systems of Uranus and Neptune are made of really dark material, so also don't reflect much light in our direction.
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$\begingroup$ Also, the mass of the material in the rings of Saturn is about 3 to 8 orders of magnitudes greater than that of Jupiter's and the rings of Uranus and Neptune probably even have less than that (I couldn't find mass estimates). Rings may be a temporary phenomenon resulting from collisions with moons (and some outgassing) so the amount of material at a given time may just be a function of the total amount of matter orbiting a planet and random luck. The type of material making up the rings may depend on where in the proto-planetary disk the planet condensed. $\endgroup$ Jun 28, 2017 at 3:26
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Building on what hartacus said, there's a couple other reasons involved as well:
Uranus and Neptune are much further out:
At closest approach to earth the distance to:
- Saturn is about 746 million miles (1.2 billion km)
- Uranus is about 1.7 billion miles (2.5 billion km)
- Neptune is about 2.7 billion miles (4.3 billion km)
So Uranus and Neptune are very far away... and they're also smaller, AND their rings are not as dense.
In an amateur telescope, it's very hard to see Uranus as anything other than a small, dim, fuzzy, blueish disk. Neptune is just a blue-green dot. The rings are so insubstantial, in comparison, that they just don't stand out.
In the case of Jupiter, the problem is simply that they're so insubstantial. The Jovian rings are very thin when compared to Saturn's. Two flyby missions, Pioneer 10 and Pioneer 11, flew by Jupiter without noticing them at all.
Combined with the difference in composition and albedo, they're just not visible to smaller Earth-based telescopes.