Pluto Rings

Pluto Rings – Face The Rings That Could Have Been

Everything you see, or everything far too small to see, is a whole of atoms. Planets in a similar and simple manner are formed by aggregation of atoms and small particles in big time scales.

What it takes for small particles to evolve to a more complex and dynamic body is the process of smaller particles coming together. And such process requires triggering sources to energize those particles, which will eventually lead to collisions, mergers and formation of planet-sized objects. In the universe, those sources are the consequences of formation of stars; which are actually conseqences of previous enchained events.

While above mentioned collisions suggest a tendency of growth in size, this is not the only case. Because as the sizes grow bigger, collisions can also result with separation, dispersion and reduction of sizes. However, it’s not only the collisions that prevent enlargement of smaller bodies.

Neptune and its rings.
Planet Neptune and its rings as seen by Voyager 2. Image Credit: NASA/JPL

How Are Planetary Rings Formed?

This is inevitably the first thing to know here.

There usually are tiny materials which are the remains of protoplanetary period, debris of previous collisions or the like. In addition to above, the particles in the universe do not just freely wander, stick together and grow into larger masses. Or just collide and crumble. Gravity has more to offer!

Consider a mass running in between Earth, Moon and the Sun. Such object will be exposed to tidal forces from three different sources. If it is weak enough and if it is exposed to such forces long enough, this will stretch the body so much that it will lose the gravitational battle and eventually break apart.

What planets do is, to form a gravitational force that aligns those particles in the form of a ring. That’s what gas giants have been doing in the past, forming relatively stable rings consisting of dust, rock and ice particles of various sizes around them.

Size of the materials constituting, their formation and the layer shapes of these rings vary depending on their structure and density; and obviously the gravitational and orbital dynamics between the host planet and the rings.

Planet Saturn.
Mighty Saturn and its glowing rings. Credits: NASA, ESA, A. Simon (GSFC), M.H. Wong (University of California, Berkeley) and the OPAL Team

Ring Systems of Different Planets

One more thing to note here is that, formation process of planets and their latter structure are highly dependent on their relative locations. Consider the best example in hand: The Solar System and how different groups of planetary objects have been formed in different regions. While bigger objects are closer to the Sun, scientists believe that sizes of planetary objects beyond Neptune are mostly limited due to the gravitational dynamics of Solar System.

And size of a planet is the primary determinant of planetary rings. Actually it’s pretty simple. The bigger mass you have, the more power you hold to break apart and/or possess other masses. That’s basically why the gas giants have their rings in the first place.

Another factor here is, as mentioned before, the collisions of such planetary bodies with each other or bigger sized asteroids. When such event occurs, it’s inevitable to experience outbursts, by which the bodies crumble to smaller particles again.

Collisions are common cosmic events frequently happening in cosmic time scales. And this is a chance for smaller bodies to be able to have cool rings. There are couple of rocky planets/moons/bodies in solar system having rings. A good example of a rocky planet with a ring is from the neighborhood; Haumea.

Planet Haumea
An illustration of Haumea with its ring. Image Credit: IAA-CSIC/UHU

Why Should Pluto Have Rings?

Does Pluto have rings? If not, why do we even mention about Pluto rings? What is this article for?

There are many reasons for such a ring system to be formed, but first we can summarize the formation process in Pluto area as follows: Scientists believe Pluto System is originated from a primordial Pluto which went through her initial phase: The growth. When this phase is considered, there are couple of things to note down.

Although planets might possess smaller particles with different dynamics, when we mention about rings of Pluto; what scientists have been referring to is a kind of collision-merger-collision-seperation cycle. It’s estimated that Pluto went through a huge collision resulting with the initial versions of Pluto and her biggest moon Charon. When it comes to smaller Pluto Moons, they were either the residues of this big collision or reached to their current formation after more and respectively smaller collisions.

Above makes quite many residues. In addition to those, scientists estimated that especially the existence of smaller moons makes it easier for the meteorites to rip off some parts of those due to low gravity. This way, such tiny particles could form Pluto rings in time.

Pluto rings
Pluto Rings! What do you think? Does she look better with the ring outfit?

Estimations Before New Horizons

However; before such estimations, even before the discovery of smaller moons, scientists did similar calculations. Possibility of a Pluto Ring System was first suggested by Stern, Tholen and Buie in 1988 and dozens of different papers were published regarding this subject from that year on.

In the article published by Steffl and Stern in 2006, “First Constraints on Rings in the Pluto System“, scientists mentioned that although the observations were limited; it’d be possible that rings might be a Pluto fact in above extent and may last for hundreds of years once formed.

Rawal and Nikouravan even went one step further and estimated existence of more Pluto moons and possible rings in 2011 (Are There Rings Around Pluto?). They did not have to wait too long before the discovery of moons Styx and Kerberos.

Pires dos Santos, in 2013, concluded that, such particles should have been totally destroyed with the effects of solar radiation in the past.

Bromley and Kenyon in 2015 approached the matter from another perspective and suggested that the smaller moons might have been born from such a ring system in the past after Pluto’s famous Big Bang.

Pluto Moons
Moons of Pluto in scale. Credit: NASA/JHUAPL/SWRI

Does Pluto Have Rings?

Another question: Why did scientists intensively search for Pluto rings in the first place?

The answer makes a vicious circle: The search for Pluto rings triggered discovery of new Pluto moons, and discovery of new Pluto moons triggered the search for Pluto rings!

How on Pluto is that possible?

After New Horizons Mission was kicked off, team scientists started to observe Pluto area using Hubble Space Telescope. Because it was essential to know if there were any kinds of objects in the trajectory of New Horizons Spacecraft that could cause any harm. And potential satellites were also included in that search.

Soon later, they found that Pluto and Charon were not alone! In 2005, scientists discovered two new Pluto Moons which were later named Nix and Hydra. And this slightly changed the game. Because,
1) All gravitational calculations about potential Pluto rings had to be re-made.
2) As we indicated before; when the meteorites hit to such small objects, the debris might float around. And this might lead to ring formation.

For this purpose, Porter and Stern also conducted another study and published an article in 2015 evaluating other possible satellites and their orbits together with possible ring formations and their locations to secure the flyby. Luckily they did not find any dangers and the flyby mission was successfully executed.

Pluto explored.
Or instead of Pluto rings, do you just prefer the naked version? Image Credit: NASA/JHUAPL/SWRI

New Horizons Mission Was There To Answer

With the New Horizons Pluto Flyby, we learned more about Pluto System than ever. And days before the flyby, mission team verified that there were no objects/rings/debris/dust formation to endanger the mission.

Actually the mission and the following studies showed that the area was as less dense as an ordinary interplanetary space environment! And most of the scientists believe that, even if such formations intend to originate, they are quickly sweeped off by solar radiation pressure.

But what if there were rings including particles smaller than detection limitations of various New Horizons Spacecraft devices?

This possibility could also be ruled out by calculations, but given the complexity of Pluto System; it’s hard to eliminate this option. However the general idea is, such small particles are, one way or another, destroyed.

Did Pluto Have Rings Before?

Although Pluto System was clearly laid bare with the New Horizons Mission, it provided new mysteries as well.

Pluto explored by New Horizons Spacecraft
Yeah, it was! Credit: NASA/JHUAPL/SWRI

According to Smullen and Kratter‘s study in 2016, there should be 14 to 42 pcs ejected icy bodies following the Pluto Big Bang with radius bigger than 10km.

Even if those bodies are lost/destroyed or not (why would they?!), researchers believe that in any case Pluto System had a ring system or irregularly wandering particles once considering the amount of debris created after the famous big collision. And it took time to clear the debris.

But what about today? May Pluto have rings the next time we look at her?

Researchers have been working on this as well.. So did Kenyon and Bromley and published the conclusions of their researches in August 2019. According to their calculations, that can only be possible with objects bigger than 10-20 kilometers in radius; which makes a body bigger than half of Pluto’s moons. In other words, objects smaller than this radius will be sentenced to death.

Above studies also show how Pluto System is cleared off from tiny particles. So in general, what researchers conclude is; even if a big collision occurs in the future for some reason, gravitational dynamics will make them go away without forming a systematic Pluto ring.


  • 10-2006, “First Constraints on Rings in the Pluto System
    A. J. Steffl, S. A. Stern
  • 9-2011, “Are There Rings Around Pluto?
    J. J. Rawal, Bijan Nikouravan
  • 07-2015, “Evolution of a Ring Around the Pluto-Charon Binary
    B.C. Bromley, S.J. Kenyon
  • 5-2015, “Orbits of Potential Pluto Satellites and Rings Between Charon” and Hydra
    Simon B. Porter, S. Alan Stern
  • 6-2015, “On the Existence of Regular and Irregular Outer Moons Orbiting the Pluto-Charon System
    Erez Michaely, Hagai B. Perets, Evgeni Grishin
  • 9-2016, “The Fate of Debris in the Pluto-Charon System
    Rachel A. Smullen, Kaitlin M. Kratter
  • 9-2017, “The New Horizons and Hubble Space Telescope Search For Rings, Dust, and Debris in the Pluto-Charon System
    Tod R. Lauer, Henry B. Throop, Mark R. Showalter, Harold A. Weaver, S. Alan Stern, John R. Spencer, Marc W. Buie, Douglas P. Hamilton, Simon B. Porter, Anne J. Verbiscer, Leslie A. Young, Cathy B. Olkin, Kimberly Ennico, New Horizons Science Team
  • 8-2019, “A Pluto-Charon Sonata III. Growth of Charon from a Circum-Pluto Ring of Debris
    Scott J. Kenyon, Benjamin C. Bromley
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One Response

  1. Joseph Newton February 20, 2020

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