If you’ve ever wondered how many planets have rings you’re not alone. Saturn is not the only ‘giant’ planet with rings. Neptune and Uranus also have rings but scientists don’t know how many they all have. It’s thought they range from 500 to a thousand. Jupiter however has four known rings. And scientists don’t even know how many of those are on the moons of Saturn.
The rings on Saturn are made up of water-ice particles that vary in size from boulders to household dust. The particles coalesce into small objects and then fall apart as the conditions change. Scientists have observed half of Saturn’s annual seasonal cycle during the 13-year Cassini mission. The next generation of spacecraft Webb will allow scientists to see the entire ring system during a Saturnian year.
The rings have only minimal effect on the planets. In fact they may even serve as a reservoir for shooting stars as the material from the rings falls into the planet’s atmosphere as its orbit decays. The rings on Saturn for example would be visible on the planet itself if the ring system were thick enough. On the other hand the rings on other planets could be more faintly visible but still not as prominent as the planet itself.
These rings formed along with the planet and its major moons. Because material that comes close to the planet does not coalesce into a moon it spreads out into a ring. Close calls with other moons can result in the planet’s gravitational tidal force breaking up the bodies and creating a ring system. The ring system is a perfect example of how close the collision of two bodies can be.
How many planets have rings? This is a question that has plagued astronomers for centuries. Many scientists believe that rings are the result of collisions between the planet and a massive object twice the mass of Earth. This collision tipped Uranus’ axis permanently. However other scientists say the rings may be a result of orbital tilt which has not yet been proven. This debate has led to a lot of speculation.
The answer depends on which definition you use. A planet may have several different types of rings each with its own origin story. In general rings are formed at the same time as the planet and its major moons. As a result the material that would form a moon is too close to coalesce forming a ring. Sometimes a planet has a close encounter with a moon which results in the body breaking up in the collision and fragmenting the remaining material.
There are eight primary planets in our solar system. Pluto was recently demoted to a dwarf planet. Four of those planets have rings with Saturn having the most extensive collection. There are hundreds of billions of planets in the Milky Way galaxy. And even more may exist beyond this. The question of how many planets have rings has remained a mystery until NASA’s James Webb Space Telescope launches in 2021.
In our solar system we have found the rings of Saturn Jupiter and Neptune. These ring systems are comprised of ice rock and dust ranging in size from a micrometer to the size of a house. Saturn is the largest of these planets with a ring system that extends out to a thousand times the diameter of the Earth. Scientists have known about Saturn’s rings for a long time but it was only in the 1970s that ring systems were discovered around other gas planets.
Although we don’t know exactly why planets have rings we do know that they formed at the same time as the planet and its major moons. If the planet has a large moon material that would make a moon can’t coalesce into a moon and instead spreads out into a ring around it. Alternatively a planet may have had a close call with another planet which can result in a dense ring of debris. This debris then coalesces into a moon.
The rings of Saturn are thin in comparison to their larger cousins but their size and composition make them easy to observe. They range between 32 feet and 0.6 miles thick and contain 99 percent water ice. The ice particles are only a few inches across. This makes them visible in close-up images and is one of the reasons why the rings of Saturn are so popular. If you have ever wondered how rings formed you can find out the answer using the Hubble Space Telescope.
Scientists believe that the planet Deimos has rings because it was affected by a past ‘grandparent’ moon. This moon was so massive that it tilted Deimos outward. In fact the outer moon had 20 times more mass than Phobos a 200-pound person would only weigh three ounces on the surface of Phobos. The outer moon orbited the planet over three billion years ago and the ratio of the two orbits interfered with gravitational interactions.
Scientists believe that the planet Deimos was part of a ring system that pushed an object 20 times larger than Phobos outward. However Phobos did not make it to Mars and it was likely pulled apart by Mars’ gravity. The debris then formed the rings around Phobos. In theory this would cause Deimos to tilt and the ring to grow. This process could have taken two more ring-moon cycles to lead to the current Phobos.
In the Book ‘Abaddon’s Gate’ the Rocinante crew is in the process of returning to Tycho Station and their mission is halted by the destruction of Deimos. This is also where the Deimos Ring is discovered. The SETI Institute has not only looked for alien life but also studied Deimos’ formation. The research team believes that the two moons formed around the same time.
We’ve heard that Saturn has a ring system but what are the reasons for their existence? A ring system is created when a planet and its major moons form at the same time. Those bodies can’t coalesce so they spread out into orbits in the form of a ring. Planets with close encounters with other bodies however can form a ring system as a result of the gravitational tug of war.
Some scientists believe that the rings surrounding a planet were formed after comets were captured by the planet’s gravity. Since comets are relatively young their formation dates are relatively recent. The ring on Saturn was formed about 3 Gyrs ago although measurements from the Cassini mission indicate that the rings formed much younger. This suggests that they formed over a longer time period than previously thought. If that’s the case how many planets are there?
Cassini’s observations of Saturn’s rings have revealed propeller-like features. These features are hundreds of miles long and were first observed by the mission in 2006. These propeller-like features are caused by the gravitational influence of moonlets which are chunks of ring material around one kilometer in diameter. The moonlets are much smaller than the moon itself and the surrounding ring particles are launched hundreds of feet above and below them.
When it comes to rings on the surface of a planet the answer is probably more than one. We know that Jupiter has four of them but how did they form? These rings are composed of dust that’s hard to spot without a backlit Sun but we also know that they were formed when meteors hit Jupiter’s inner moons and kicked up dust. That’s how Jupiter got its four rings.
The rings on Saturn and Jupiter likely formed as the result of meteors that crashed into their inner satellites which orbit the planet for many years. We can trace the rings to the inner satellites of Jupiter and Uranus through the Galileo space probe. Saturn’s rings are probably the result of debris from a collision between the ringed planet and its icy moon. Earth is also acquiring its own ring system.
So what planets have rings? Saturn Uranus and Neptune are all known to have rings. But the fourth planet Jupiter also has rings. The ring system on Saturn is the most beautiful in the solar system. Other gas giants such as Uranus and Neptune have rings as well. It’s even possible that Pluto and Rhea have rings. And if Jupiter and Saturn have rings then Mars might as well.