That's No Moon -- Okay No Wait That's a Moon
September 29, 2016 1:33 AM   Subscribe

There are 182 moons (and counting) in the solar system orbiting planets; there are a bunch more orbiting planetoids. Read on for all your moon facts.

Mercury and Venus have no moons; if moons were close to the planets they'd be destroyed by tidal forces, but if they were far from the planets they'd be captured by the sun and devoured. Venus may have once had a moon, but doesn't now; late Renaissance astronomers thought it maybe did, but were wrong.

Earth has a moon, but it's a very strange moon. It's the fifth-largest moon in the solar system and by far the largest moon compared to the body it orbits. Earth's barycenter with Luna is only just barely inside its own mass; some proposed definitions of planets would promote Luna to a planet. It is the only moon -- and only celestial body other than Earth -- that has been visited by humans. It was probably knocked off the Earth four and a half billion years ago.

Mars has two moons, among the smallest in the solar system -- Phobos (fear) and Deimos (panic), after the horses that pulled the war god's chariot. Both are potato-shaped moons, too small to pull themselves into spheres (Deimos is smaller than Mt. Everest; Phobos is smaller than Luxembourg). Phobos will eventually fall and crash into Mars; Deimos will eventually be pulled away by the sun. Phobos and Deimos may have formed with Mars in the early solar system, or may have been large asteroids captured by Mars later on. Phobos has a monolith that makes conspiracy theorists excited (but is just a rock).

Jupiter is the king of the solar system at 67 named moons. Ganymede, Callisto, Io, and Europa are visible with binoculars or amateur telescopes, and are known as the "Gallilean moons" because they were the four Galileo could see in 1610 with his telescope; no further moons were observed until 1892. (Although it's possible that Gan De observed Ganymede in 365 BCE by the clever method of obscuring Jupiter with a tree branch and observing its companions.) Ganymede is believed to have a saltwater ocean and a magnetosphere, although its magnetosphere is wholly within Jupiter's; Io is volcanically active; Europa has (as of Monday!) water jets spewing forth from its south pole. A further four -- Metis, Adrastea, Amalthea, and Thebe -- orbit regularly and close to Jupiter. The rest are irregular objects with inclined or eccentric orbits. Jupiter's moons are named after Zeus's lovers and their children, and there are plenty. (NASA sent his wife, Juno, to check up on him, and you can see her movie of his four Galilean moons here.)

Saturn, better known for its rings (made of highly-reflective ice) than its moons, takes second place with 62 named moons. Originally named after Titans and Greek giants, their sheer number has demanded the addition of Norse, Gallic, and Inuit giants to their numbers. The most interesting are Titan, Saturn's largest moon and one of the few moons with an atmosphere; Enceladus, a small moon (for a gas giant) that's geologically active and possesses water; and shepherd moons, which help the rings keep their forms and gaps.

Uranus, mother of 27 moons, names its moons for characters from Shakespeare's plays. Among the most interesting are Titania, Miranda, and Oberon.

Neptune's 14 moons are named for Greek water dieties, and by far the largest is geologically-active Triton, discovered just 17 days after Neptune itself and 100 years before the next Neptunian moon.

Pluto and Charon orbit around a barycenter that is outside Pluto (part of the evidence that Pluto isn't a planet).

Can moons have moons? Yes, but they tend to crash into the body they're orbiting rather quickly.
posted by Eyebrows McGee (45 comments total) 53 users marked this as a favorite
 
Of all the MeFites I ever thought I might be mooned by, you were never one.
posted by oneswellfoop at 2:02 AM on September 29, 2016 [2 favorites]


This moon post is out of this world! (Which, as I've learned thanks to this post, might make it a planet post instead)

It seem s like people want to keep redefining planets so that Pluto is a planet and the moon isn't a planet. Or that Pluto is a planet but Ceres isn't and so on.
Just give it up, Pluto is not and never was a planet.

I like the moons having moons post.
I'd love to see a little theoretical model of the most stable moons in moons in moons in moons system, like how deep can you nest your moons in a stable system.
posted by Just this guy, y'know at 2:57 AM on September 29, 2016


Both are potato-shaped moons

Well maybe potatoes are Martian-moon-shaped. Did you ever think of that, huh? The French should be calling them pommes des lunes de Mars instead of pommes de terre.
posted by XMLicious at 3:07 AM on September 29, 2016 [7 favorites]


That's almost one moon per country - given countries are almost as hard to define as are solar system objects.

Perhaps each country could adopt a national moon, or each moon could have its own TLD and set up a server on the NASA interplanetary internet. A Raspberry Pi for every planetoid! (Well, except Europa. Attempt no LAN thing there.)
posted by Devonian at 4:21 AM on September 29, 2016 [13 favorites]


We Like the Moon

Plus, one of my favorite video games series, Marathon, is based on a colony ship of the same name that was built out of Deimos. So, it didn't get pulled away by the sun, although it did get taken over by the Pfhor.
posted by Halloween Jack at 4:29 AM on September 29, 2016


Just a very pedantic correction to an excellent post: most of the moons of Uranus are named after characters from Shakespeare, but a few (Umbriel, Ariel, Belinda) are named after characters in Pope's The Rape of the Lock. Carry on.

As a side note/addendum, not only does Titan have an atmosphere as you mention, it also has surface lakes and seas! (It has rain of a sort, too.) I mean, the lakes are made of ethane and methane and the temperature is -180 C, but still. I also kinda feel like people forget that we sent a lander there.
posted by chalkbored at 4:33 AM on September 29, 2016 [3 favorites]


I misread this as 182 moms. That is all.
posted by dame at 5:12 AM on September 29, 2016 [1 favorite]


To put it in perspective, here's an image of all the known objects in the solar system over 200 miles in diameter (as of 2007ish). Lotta real estate out there.
posted by sexyrobot at 5:25 AM on September 29, 2016 [2 favorites]


I also kinda feel like people forget that we sent a lander there.

I know! The only landing on a moon other than our own, one with the only surface oceans other than ours, one with active carbon chemistry, the most distant landing ever - more than a billion kilometres away - and the only one in the outer solar system, and ten years on who can even spell Huygens?
posted by Devonian at 5:25 AM on September 29, 2016 [3 favorites]


Ganymede is believed to have a saltwater ocean

An underground saltwater ocean, and I bet it's pretty cold. Syd Barrett clearly knew about it in 1967.
posted by sfenders at 5:42 AM on September 29, 2016


Well, I think the fact that Huygens only operated for 90 minutes or so after landing might be contributing to its lack of popularity. To the extent that Curiosity (for instance) is a household name, that's mainly due to the fact that it's still rolling around lasering rocks.
posted by tobascodagama at 5:47 AM on September 29, 2016


"Perhaps each country could adopt a national moon"

I would like to propose the UK adopt Europa as it's national moon, just to annoy UKIP.
posted by Just this guy, y'know at 5:53 AM on September 29, 2016 [6 favorites]


Okay No Wait That's a Moon

Are you sure?
posted by misteraitch at 5:56 AM on September 29, 2016


Truly Titan is a moon to Huygens kiss.

(This doesn't even really work, but my brain just can't help it whenever I see Huygens)
posted by Just this guy, y'know at 5:57 AM on September 29, 2016


Pedantic note: Pluto is a planet, despite whatever ginned up definition some deluded scientists want to insist on.
posted by Brandon Blatcher at 5:59 AM on September 29, 2016 [3 favorites]


Pluto is not and never was a planet.
posted by Just this guy, y'know at 6:03 AM on September 29, 2016 [2 favorites]


Earth's barycenter with Luna is only just barely inside its own mass; some proposed definitions of planets would promote Luna to a planet

Huh, never that. Mind is currently being blasted into space like it was hit by a new thought 1/4 the diameter of the brain.
posted by Brandon Blatcher at 6:06 AM on September 29, 2016 [2 favorites]


I remember when I was a kid learning that Jupiter had 16 (I think) moons, and wow, that seemed like a lot of moons at the time.
posted by Pater Aletheias at 6:13 AM on September 29, 2016 [2 favorites]


if we can have dwarf [planets maybe some of those "moons" should be downgraded to dwarf moons.
posted by BentFranklin at 6:14 AM on September 29, 2016


Dwarf planet is an odd title, since the definition means the celestial body is not a planet. Make up your mind, science definers!

I proposed we change dwarf planet to 'Tyrion'. That sounds so much better.

"The Kupier belt has many Tyrions"
"Object P4928-1938 is Tyrion with a dull red color"
posted by Brandon Blatcher at 6:19 AM on September 29, 2016 [1 favorite]


As for interesting moons of Uranus (12 year-old giggle), how could you forget Triton? It has a retrograde orbit, is geologically active and has pluuuuuuumes!
posted by Brandon Blatcher at 6:26 AM on September 29, 2016


Real moon enthusiasts prefer Miranda.
posted by Jessica Savitch's Coke Spoon at 6:27 AM on September 29, 2016


Miranda is last century. Talk to me when it gets some pluuuuuuumes.
posted by Brandon Blatcher at 6:32 AM on September 29, 2016 [1 favorite]


Fantastic FPP, thank you!
posted by OrangeDisk at 6:36 AM on September 29, 2016


Everybody loves a pluuuuuuuume!
posted by Eyebrows McGee at 6:53 AM on September 29, 2016


itsnameisthemoon.com
posted by kiltedtaco at 7:00 AM on September 29, 2016 [3 favorites]


"As for interesting moons of Uranus (12 year-old giggle), how could you forget Triton? "

'Cause I remembered it was a moon of Neptune!
posted by Eyebrows McGee at 7:01 AM on September 29, 2016 [3 favorites]


D'oh! I musta been sniffing too many pluuuuuuuumes!
posted by Brandon Blatcher at 7:03 AM on September 29, 2016


Nice post!

In addition to bootprints on Mars, I would really love to see some more robotic landers on some of these moons during my lifetime. Specifically a Europa lander with something that can drill or melt through the ice and take a peek underwater.

But what if we send something underwater and there's a race of beings there that are like that race of people in one of the HGTTG books. Their planet was covered with clouds so they had never even considered that there was anything beyond their own planet and when something came crashing down from above it threw their whole society into chaos. What if there are some intelligent creatures on Europa who had never considered there was something above the ice?

Fully-formed creatures would be nice but just a smattering of bacteria would be a whole lot of fun to find.
posted by bondcliff at 7:15 AM on September 29, 2016


What if there are some intelligent creatures on Europa who had never considered there was something above the ice?

I've wondered about this also. Any sort of sentient creature would probably have no idea about something existing 60-100 miles beyond the walls of ice. The places where water escapes into plumes would probably be sort of no-go zone or ritual burial/trash spot. Something, anything, coming through that "wall" would seriously mess with the emotional and physical being.

Can you imagine if creatures suddenly emerged from a spot 100 miles below the crust? Humanity would collectively lose its mind, at least for a while.
posted by Brandon Blatcher at 7:22 AM on September 29, 2016


Aaaand I just imagined creatures with bubble feet walking upside-down on the ice...
posted by sexyrobot at 7:39 AM on September 29, 2016 [2 favorites]


> Just a very pedantic correction to an excellent post: most of the moons of Uranus are named after characters from Shakespeare, but a few (Umbriel, Ariel, Belinda) are named after characters in Pope's The Rape of the Lock. Carry on.

Just a very pedantic correction to your pedantic correction: Ariel is also a character from Shakespeare. Carry on.

Also: astronomically great post!
posted by languagehat at 7:41 AM on September 29, 2016 [3 favorites]


Any sort of sentient creature would probably have no idea about something existing 60-100 miles beyond the walls of ice.

In the ancient near east (and probably other ancient societies) the sky was thought to be a firm dome, with the heavens above it. You get lots of little hints of this in the Bible. The flood happens in God opens the flood gates in the sky and lets the waters of heaven fall through and overwhelm the earth. Or Elihu's words in Job 37:18, "Can you, like [God], spread out the skies, hard as a molten mirror? Or, in a related the-sky-is-some-kind-of-solid-canopy image, the Egyptian goddess Nut is sometimes portrayed as herself forming the sky with her own starry body, crouching over the earth.

All of which is to say, I bet you'd get some really interesting theology/cosmology from sentient life floating in the frigid seas under the literally icy dome of Europa.
posted by Pater Aletheias at 7:47 AM on September 29, 2016 [1 favorite]


Pluto is not and never was a planet.

Is, was, and ever shall be a planet without end. Amen.
posted by The Tensor at 7:54 AM on September 29, 2016 [2 favorites]


the sky was thought to be a firm dome

And still is, for many practical purposes. All the math used in Celestial Navigation essentially bases it's approach on the stars in the sky being in fixed locations. At the mind imploding distances of the universe the calculable change in the position of stars is fixed solid for many years if not millenniums. I don't know but I'd expect rocket navigation from celestial sightings (how do they do that) uses essentially the same principle of a "fixed" dome like sky.

Great post!
posted by sammyo at 7:59 AM on September 29, 2016


The trouble with landing capable robots on very low melting point ice is that active robots are hot, hot, hot and will sink, sink, sink. Better, at least for now, to fly them through the pluuuuumes and have then sniff daintily.

And the trouble with landing humans on places that may have had life on them is that humans shed bio-matter like bastards. Which probably won't lead to invasive species, but will mess up the science something dreadful. Mars landers are clean, clean, clean - it's a lot harder to sterilise Buzz and company, and there'll be no leaving those fecal containment bags on Mount Olympus, no shit. (Which would have rather mucked up The Martian, but there we go.)
posted by Devonian at 8:08 AM on September 29, 2016


Per the shadow biosphere hypothesis, we might even shed things that would look like alien life to us because we just haven't noticed them yet on Earth.
posted by XMLicious at 8:36 AM on September 29, 2016 [1 favorite]


Jupiter [has] 67 named moons. . . .

Saturn . . . takes second place with 62 named moons. . . .

Pluto and Charon . . .


When I was in high school, Jove had 12 and Saturn 10 or 11. Charon hadn't been resolved as a separate body from Pluto yet, either. My father was born before Pluto was discovered, when the distinction between galaxy and universe was still a little vague. That's one (rather long) human lifetime.

Pluto and Charon orbit around a barycenter that is outside Pluto (part of the evidence that Pluto isn't a planet).

Thanks, Obama!
 
posted by Herodios at 8:43 AM on September 29, 2016


Fully-formed creatures would be nice but just a smattering of bacteria would be a whole lot of fun to find.

As thrilled and excited as I am about sending something to Europa to explore, I'm a little worried about what we leave behind with our probes. I'm all for the exploration and the effort, but I'm hoping we're not going to leave some sort of toxic/radioactive device lying in Europa's waters if there is life there (or the potential for it). I mean, I don't expect that we're going to find an alien civilization, but I also don't want our explorations to trigger an extinction event there either. Though I guess the reverse might also be possible, that there isn't anything there, and a probe is what introduces the final ingredients for life.
posted by nubs at 9:01 AM on September 29, 2016 [3 favorites]


> As thrilled and excited as I am about sending something to Europa to explore, I'm a little worried about what we leave behind with our probes.

You need to be in the Europa plumes thread! There are concepts for spacecraft sample missions that only dive through the plumes ejected into space, scooping up samples as they go. At the end of the mission, it's a deep dive into the parent gas giant, where the spacecraft will be sterilized and crushed without any contamination issues.

But yeah, people have seriously considered planetary contamination and have very detailed protocols to address the concerns.
posted by RedOrGreen at 9:15 AM on September 29, 2016 [1 favorite]


Yeah I should have linked some previously pluuuuuuumes! but I got excited and forgot.
posted by Eyebrows McGee at 5:54 PM on September 29, 2016


Thanks RedOrGreen; I figured people way smarter than me would be working on it.
posted by nubs at 6:31 PM on September 29, 2016


I like the moons having moons post.
I'd love to see a little theoretical model of the most stable moons in moons in moons in moons system, like how deep can you nest your moons in a stable system.


At a certain number of moons with moons with moons, we could define this as a matryoshka system.
posted by bryon at 9:19 PM on September 29, 2016 [1 favorite]


Huh, There is a moon of Uranus called Sycorax.
Just like the Doctor Who Aliens.

Are there any other Who Aliens named the same as moons?
According to wikipedia and a spreadsheet I just made Janus is a moon of Saturn and also an Alien race (first seen in the episode Face the Raven)

So yeah.
I should be working.
posted by Just this guy, y'know at 5:39 AM on September 30, 2016


bondcliff: "But what if we send something underwater and there's a race of beings there that are like that race of people in one of the HGTTG books. Their planet was covered with clouds so they had never even considered that there was anything beyond their own planet and when something came crashing down from above it threw their whole society into chaos."

Krikkit, in Life, The Universe, and Everything. There is a dust cloud that surrounds the solar system, for Reasons.
posted by Chrysostom at 7:57 PM on October 5, 2016 [1 favorite]


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