Ah, moons. So often overshadowed by your rocky, gassy, and thermonuclear overlords, you help invoke tides, stabilize axial tilts, sculpt and replenish rings, and provide at least one species with a stepping stone to timidly venture from the safety of their home planet. In this article we pay tribute to all those underappreciated planetary custodians by recognizing five of the downright weirdest moons in the solar system.

1. Titan (Saturn)

Imagine a dreamy world with clouds, wind, rain, rivers, lakes, shore lines, sand dunes and seasons, and this distant moon of Saturn is probably the last destination that springs to mind. Titan not only exhibits all of these familiar characteristics, but it is also the only moon known to have a thick atmosphere – composed mostly of nitrogen too, just like Earth.

That’s where the similarities just about end, though. If you excitedly read the paragraph above, hopped into the nearest spacecraft, journeyed the 750 million miles to Titan, landed on the surface and casually strolled outside to stretch your legs or go for a swim, you might be in for an unpleasant surprise. With no oxygen to breath, its thermostat set to a chilly -179° Celsius, impenetrably dim, hazy skies and vast lakes filled with liquid natural gas; Titan offers a fairly unforgiving environment for life as we know it.

2. Io (Jupiter)

Like a cosmic game of tug o’ war, Io is gravitationally pulled in several directions at once by its parent planet and fellow Galilean moons. All this interaction generates a heck of a lot of internal heat that eventually needs to be released. As a result, the Jovian moon is currently the most volcanically active body in the solar system. The tidal forces inflicted on Io are so strong that its solid surface may contract and expand as high as 330 feet, as opposed to Earth’s comparatively pathetic high and low tides of about 60 feet.

3. Europa (Jupiter)

It’s been about 30 years since hydrothermal vents were discovered in Earth’s oceans, and along with them the first community of organisms that relied on minerals and bacteria extracted from deep within the planet to survive, rather than sunlight. As evidence began to mount that a liquid water ocean could exist beneath Europa’s icy crust, so then did the possibility of finding life beyond Earth.

The same processes responsible for turning Io into an overflowing cauldron of silicate and sulphur could also play a key role in keeping Europa warm enough for microbial life to survive in a sub-surface ocean. Unfortunately, sending Bruce Willis and his crack team of oil drillers to find this ocean would be a mission somewhat difficult for NASA to justify in today’s economy, so we may have to wait a decade or two before probes can investigate the moon a little closer to make sure it’s worth the effort.

4. Mimas (Saturn)

I could rattle off a few mildly interesting facts about this moon, like how it’s largely responsible for creating the famous Cassini Division in Saturn’s rings or that it was almost shattered by an enormous impact that left a 130-kilometer-wide crater; but you’re probably staring blankly at the picture above, wondering if you should stock up on canned goods and hustle your family into a bomb shelter to await inevitable invasion by the Galactic Empire (coincidence? Or… cosmic conspiracy?!). FYI: My bunker has Wi-Fi.

5. Triton (Neptune)

Billions of years ago Triton is thought to have existed as one of two nameless, oversized snowballs in the Kuiper Belt, happily traveling around the sun while orbiting a common center of mass with its companion. At some point in time this duo moved a little too close to Neptune and the gas giant’s superior gravity proceeded to capture what is now Triton by wrenching the object out of its heliocentric orbit, subjecting it to a future of planetary subordination. One of the repercussions of this traumatic event is also what makes Triton so unique; it is the only large moon in the solar system that has an orbital direction opposite to that of its planet’s rotation – also known as a retrograde orbit.

Unfortunately for Triton, its orbital energy is being steadily depleted by the conflicting influence of Neptune’s rotation. As a result, the moon is gradually drifting closer to Neptune, all but ensuring one of two unhappy fates: breaking apart due to tidal forces or violently crashing into Neptune in a mere few billion years.

Saturn’s North Pole (Cassini-Huygens, 2007 and 2008)

In November 1980, planetary scientists eagerly examined transmissions received from the Voyager 1 spacecraft as it sped past Saturn. And with good reason! Amid those transmissions was the first image of Saturn’s North Pole – a region that’s virtually impossible to see from Earth, and, depending on the degree by which Saturn is tilted, can be cloaked in darkness for up to 15 years at a time (and you thought your last winter was never going to end).

What those scientists saw, and later missions confirmed, was a decidedly bizarre feature in the gas giant’s atmosphere directly above the North Pole: a 15,000-mile-wide hexagon.

At this point, before we lose all but Weird Thing’s distinguished geometry geek readership (you know who you are, you magnificent bastards), it’s worth pointing out that hexagons naturally occur all over the place: basalt columns; beehive honeycombs; snowflakes; and even molecules offer some examples. Unfortunately the processes responsible for these formations by no means explain the feature on Saturn.  In fact, the planet’s thick atmosphere is one of the last places experts were prepared to find such a geometric oddity – even its South Pole has a reassuringly circular, terrifyingly enormous hurricane churning up the clouds.

A Comparison of Saturn’s Poles (Cassini-Huygens, 2008)

So why is it there? Besides dropping Jodie Foster – or, ideally, Matthew McConaughey – into the middle of the 60-mile-deep hexagon and seeing where she goes, a slightly less exciting experiment conducted by the Niels Bohr Institute in Denmark provided some intriguing results. And by slightly less exciting, we mean they stirred a bucket of water. What they found was that at certain speeds the water flow would interact with the edges of the cylindrical container to create rotating polygons with up to 6 corners.

As you may have already guessed, the experiment has a long way to go before it explains Saturn’s hexagon. For one thing, a colossal bucket isn’t sitting at the North Pole to provide distinct boundaries for the planet’s many complex layers of clouds to interact. Scientists have yet to figure out precisely how Saturn is creating a similar result with its multifaceted toolkit of jet streams and waves. Perhaps a more relevant explanation may be found in satellite observations of Hurricane Isabel (PDF) from 2003, wherein the storm’s eyewall alternated between pentagonal and hexagonal formations through unique combinations of smaller rotational features called mesovortices; showing us that even home grown storms can test and inevitably improve our equations of motion.

Satellite Observations of Hurricane Isabel in 2003 (PDF)

We’ll probably have plenty of time to figure out Saturn’s hexagon though. One of the most profound mysteries surrounding the formation (second only to its existence in the first place) is that it has stuck around as a stable feature in the 29 years or so since Voyager first observed it. As Saturn is currently in the unhurried process of tilting its North Pole towards the sun, scientists can soon point the Cassini-Huygens spacecraft’s superior optical instruments at the newly illuminated region to assist the relentless effort to discover answers (or more questions). Until then, we hope you’ll join us in simply appreciating this hexagon as one of the many weird things that makes our universe even more fascinating.