Planetary Accessories — Moons and Rings

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In our Solar System, we are used to a certain order of things. Our terrestrial planets, Mercury, Venus, Earth and Mars, i.e. the little ones, have zero, one or two moons. Jovian planets, the big ones, Jupiter, Saturn, Uranus and Neptune, have lots of moons and rings, some more extensive than others. The idea of small rocky planets having rings may sound a bit weird. Just imagine looking up at the sky and seeing rings across our sky…

Well, it appears that Mars might be trading in a moon for some rings, though not anytime soon. Researchers at the University of California Berkeley have examined Mars and its two moons, Phobos and Deimos, and they have concluded that the moon Phobos might eventually break up, with some of its parts settling down as a ring around Mars.

Both Phobos and Deimos are small moons, and Phobos appears to be somewhat porous and brittle, a condition which might eventually lead to its doom. Planets and their moons are connected gravitationally, much like stars and their planets. Using Earth and the Moon as an example, both are exerting a gravitational force on each other. One effect of this force is the tides we see in many coastal regions on Earth.

Mars has the same gravitational interaction with its moons. As it turns out, Phobos is slowly spiraling inwards, so it is getting closer to Mars. This means that the gravitational force between Mars and Phobos is increasing. There will come a time when this gravitational force between Mars and Phobos will exceed that of the particles of Phobos to each other, at which point Phobos will break apart. Some parts will undoubtedly impact on Mars, but some would settle into Mars orbit as a ring. The image below shows what that might look like. Of course this will not happen for a few tens of millions of years, so don’t dig out your telescope for that just yet.

Figure 1: (left) Mars’ moon Phobos. (right) Mars with a ring. Credits: UC Berkeley, NASA.

In Star Trek, especially in the remastered versions of the episodes, we have seen a few inhabited terrestrial planets with rings. One example was Gamma II in the “The Gamesters of Triskelion,” a cratered planet with rings.

Figure 2: The planet Gamma II in “Gamesters of Triskelion.” Credit: Memory Alpha.

Another example was Zeon M34 Alpha system, featured in The Original Series episode “Patterns of Force.” This planet was threatened by the Nazi-like regime from the other inhabited planet in the system, Ekos.

Figure 3: The planet Zeon in “Patterns of Force.” Credit: Memory Alpha.

Another planet with rings we saw in Star Trek was Mudd’s Planet, the origin of Harry Mudd’s androids.

Figure 4: Mudd’s Planet in “I, Mudd.” Credit: Memory Alpha.

In Deep Space Nine, Jadzia Dax planned her honeymoon with Worf on a ringed world called Casperia Prime, a resort planet much like Risa.

Figure 5: The planet Casperia Prime in “Change of Heart.” Credit: Memory Alpha.

In the very last TOS episode “Turnabout Intruder,” Dr. Janice Lester used a machine invented by the long-dead natives of Camus II to briefly trade bodies with Captain Kirk. Camus II was portrayed as a ringed world.

Figure 6: The planet Camus II in “Turnabout Intruder.” Credit: Memory Alpha.

In “Up the Long Ladder” the Enterprise D visited Mariposa, an inhabited ringed world in the Ficus sector. This world was to be the home of colonists from Bringloid V.

Figure 7: The planet Mariposa in “Up the Long Ladder.” Credit: Memory Alpha.

In Star Trek Insurrection, the Enterprise D visited the planet Ba’ku. The rings around the planet emanated a particular kind of radiation that gave the inhabitants perfect health and virtual immortality.

Figure 8: The planet Ba’ku. Credit: Memory Alpha.

The planet Tantalus V was the site of a Federation rehabilitation colony, to which the Enterprise delivered supplies in “Dagger of the Mind.” In the two images below we can see very nicely the rings from orbit and from the planetary surface.

Figure 9: The planet Tantalus V in “Dagger of the Mind.” (left) from orbit, (right) from the surface. Credit: Memory Alpha.

And finally, the exoplanet hunters have found one world (a gas giant though) that has a rings system much more extensive than that of Saturn. It may take a bit more time before we can detect rings systems around smaller, Earth-like planets. I can’t help but wonder what it might be like to live on a world with rings.

Figure 10: The ring system of exoplanet J1407b. Credit: Ron Miller, University of Rochester, and Leiden Observatory.

Here are a few links for you if you’d like to know more about this topic.

Mars to lose its largest moon, but gain a ring

Gigantic ring system around J1407b much larger, heavier than Saturn’s

Memory Alpha:

If you are interested in hearing more about the latest discoveries in the physical sciences and technology in a fannish setting, come visit us at Shore Leave next July. This fan-run convention features over 12 hours of science programming, in addition of course to all the usual con activities. For more information please visit

Inge Heyer

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