TUCSON, Ariz. — Humans first explored the Earth’s moon 50 years ago, an impressive feat for sure. But if you are interested in venturing a little off the beaten path, here are some other extraordinary moons humans may be able to visit in the future.
Pit Stop on Phobos
Your guide: Alfred McEwen, UA Regents’ Professor of Planetary Sciences and principal investigator of HiRISE, the sharpest camera ever sent to another planet.
As you pack up your spaceship in preparation for decades of travel, you’re sure to feel like you’re forgetting something. Don’t worry! After about nine months of listening to “are we there yet” – even when traffic is at its lightest and Mars is at its closest to Earth – one of the red planet’s moons, Phobos, is the pit-stop you need.
Although its origin is still disputed, Phobos could be a specific type of captured asteroid that is rich in water, a valuable resource for space exploration and mining. While you’re buying replacement chargers and anti-nausea pills, let the kids out to stretch their legs on this seven-mile-wide moon. As they leap about in gravity about 100 times weaker than Earth’s, you should fill up your futuristic fuel tanks with water stored under the Martian moon’s surface. The fuel station’s ease of access is granted by a gravitational tug much weaker than Mars’.
While you’re there, explore the disorientingly close horizons that are distorted by Phobos’ small size and rugged terrain. You’ll feel as though you are standing in an Earthly canyon and notice that its surface is surprisingly dusty, like Earth’s moon. Make sure to stop by the largest feature on Phobos, the more than five-mile-wide Stickney crater, before blasting off to the outer solar system.
Don’t want to drive? Maybe you can catch a ride: Plans are in the works for Japan to send a sample return mission to the mysterious moon.
Visit the Underworld on Io
Your guide: Alfred McEwen, interdisciplinary scientist on the Galileo mission to Jupiter
Jupiter’s innermost moon Io is a wicked place for only the most extreme thrill seekers. Most of what is known about Io comes from the Galileo spacecraft, which studied the Jupiter system in detail between 1995 and 2006. If you park your starship on the nighttime side, your eyes will first fall on sprawling lava flows glowing across the color spectrum because of the various elements melting within. Hundreds of volcanoes pockmark the surface of Io, each one more active than the most active volcano on Earth: Kilauea.
Make sure to take a tour of Io’s top sites. The Loki caldera, or sea of lava, is the largest active volcano in the solar system. Pele, named after the goddess of volcanology of Hawai’i, is smaller than Loki but is ringed by red deposits the size of Texas (where everything’s bigger) and is one of the moon’s most prominent features.
While you might not hear the grumblings of the restless moon through the tenuous atmosphere, you will feel the terrain bucking beneath your soles and the swelling solid-body tides that reach more than 160 feet! All this activity is fueled by the planet Jupiter, which Io orbits every two Earth days, and the other large moons which regularly align to tug gravitationally on Io, heating the rocks to create the magma within.
With features named after the gods and goddesses of the underworld littering the surface, you might think you’ve died and gone to Hades. But don’t fret, Io isn’t Hades, though it is a hellish place in which there are many ways to die.
You could land in a boiling caldera and vaporize. Alternatively, you could land too far away from it and freeze to death. But freezing would be a slow, sad way to leave any world, and it’s likely that on Io, you’d run out of air first. If you desperately scrambled for breath, you’d find that the thin atmosphere is actually poisonous, and your last breaths of air would smell of rotten eggs due to Io’s sulfurous surface. Yet no matter how carefully you tread across the spectacularly vivid moon, the intense radiation generated by Jupiter’s magnetic field would unrelentingly destroy your cells. The noxious surface could even challenge the hardiest of robotic spacecraft. Be prepared!
Cool Off on the Solar System’s Icy Moons
Your guide: Veronica Bray, UA Lunar and Planetary Laboratory associate staff scientist developing a seismometer for a potential Europa lander
After visiting the volcanic world of Io, cool off in the frigid waters of another Jovian moon: Europa. Upon landing, you’ll notice Europa is the smoothest moon in the solar system. An icy surface of disputed thickness floats above a briny liquid ocean. The moon’s topography varies by only about 6,500 feet. The relative lack of craters and smoothness is due to a combination of geologic activity and a warm ice shell, resulting in topographic features that relax back toward a level plain.
But before you whip out your ice skates to glide along the ruddy fault lines that cut across the surface as a result of tidal squeezing, find shelter. If you are adventurous, you could set up camp in a deep ice cave; if your tastes are more refined, you might prefer a five-star hotel carved and stabilized within the ice layer. Similar to Io, on Europa, radiation from Jupiter would wreck your spaceship and your body, but water ice acts as a protective shield.
Hopefully, you’ll book ahead for the occult submarine tours in which you try to spot a Europan giant squid, though reports of their sightings have not been confirmed. Scientists think life, even bacterial life, might thrive in warm water vents on the ocean floor warmed by tidal forces.
While you might be slightly nervous about having miles of ice and water above your head, just remember that Europa’s gravity is about the same as Earth’s moon, so the pressure will not be greater than what a submarine can tolerate in the depths of Earth’s oceans. If the depths don’t get under your skin, then it’s likely that the creaking and groans of rock-hard ice echoing through the pitch-black ocean won’t either. Europan tides are responsible for the noise.
If you decide to brave the surface, acquire a certified spacesuit that protects against radioactivity. You’ll find that about 60 craters remain on Europa, which is relatively few for a moon with no atmosphere to erode surface features. The geologic activity is so great that the surface is very young. Also on the surface you might need to dodge “penitentes,” vicious spikes of frozen snow sculpted by the dancing sun.
If frozen sea worlds aren’t your thing and you want to spend more time on land, travel to Saturn’s tiny icy moon Enceladus to catch some powder.
Like an arctic Yellowstone, geysers erupt in Enceladus’s southern hemisphere from fissures in the surface layer of ice, much like Europa. The spray of subsurface water likely supplies fresh snow for skiing, snowboarding and sledding, and the low gravitational tug of a moon with a diameter six times smaller than Europa means you can take on steeper slopes and get more air.
What to pack: Enceladus is the brightest moon in our solar system, so bring sunglasses! Snowshoes and an umbrella can protect you from sinking into the snow or getting buried as the frozen spray falls to the ground.
A Moon like Earth, Except Totally Different: Titan
Your guide: Alfred McEwen, member of the imaging science team of the Cassini mission to Saturn
Titan, Saturn’s largest natural satellite, draws astrobiologists like moths to a flame. Observations made during fly-bys of NASA’s Cassini spacecraft reveal glimpses of a mesmerizingly alien landscape of mountains, rolling hills and valleys, complete with meandering streams and lakes. Underneath its surprisingly Earth-like surface, Titan is thought to harbor a vast underground ocean of liquid water. That discovery, made only fairly recently, adds Titan to the handful of worlds in our solar system that could potentially contain habitable environments.
Titan, which is about the size of planet Mercury, offers some of the most spectacular views and experiences our solar system as to offer. For much of the final descent through Titan’s atmosphere, which is thick with an orangish shroud of nitrogen and smog, you wouldn’t see a lot. Picture Los Angeles on a really bad day during rush hour, multiply that by 1,000, and you get the idea.
As you approach the surface, though, ridges of steep mountains come into view, as do sand dunes and gullies carved by rushing liquid. At times, you’ll catch a glint from the glass-like surface of a distant lake. Once on the ground, don a heavy space suit to protect you from Titan’s harsh (in Earth terms, “polluted”) atmosphere and extreme cold before you start exploring.
Your first excursion onto Titan’s surface should be to visit a historic artifact: the Huygens lander – or what’s left of it. The only human-made object to ever touchdown on a moon other than Earth’s, the probe hitched a ride on the Cassini spacecraft with a mission to study Titan up close. Once Huygens cast off from its mothership, it hurtled toward Titan and was soon swallowed by the orange haze that hides the moon from view. Dangling from a parachute, Huygens spent two-and-a-half hours floating down toward the surface, snapping pictures with its UA-built descent imager and taking all sorts of measurements.
Next, take a leisurely trot around the shore of one of Titan’s famous lakes. Where else in the solar system could you skip rocks across an endless expanse of liquid methane? Wrap up your trip with another highlight: Strap on a set of wings and, after a brief orientation on how to steer and safely land, take off and flap to new horizons, supported by Titan’s dense atmosphere. Isn’t zip-lining so 2000’s?
Book your travel early – NASA just approved the Dragonfly mission, which will send a quadcopter to Titan in 2034.
Looking for the Fringe? Here’s a Strange Moon You’ve Never Heard of
Your guide: Erich Karkoschka, Lunar and Planetary senior staff scientist and expert on Neptune, the pale blue giant
If you’re the type who avoids tourist crowds and finds Jupiter’s and Saturn’s moons too mainstream, consider a trip to Neso. Don’t worry if you’ve never heard of it – most people haven’t. Named after the Nereids, female water spirits in Greek mythology who accompany Poseidon, god of the ocean, Neso is the fringiest of several dozens of moons that belong to the outermost planet of the solar system: Neptune (which is how the Romans referred to Poseidon).
It’s no coincidence that Neso gets short shrift in most glossy tourism ads: This strange world is so far out that nobody knows for sure what it looks like, how big it is or how long a day lasts on its surface. What is fairly certain is that none of the other known moons get as far away from their host planet as Neso does. Its orbit is so oblong that a Neptunian observer enjoying a Neso full moon would have to wait more than a quarter-century to see another. That said, it would not be a huge loss, as attempting to spot Neso from Neptune is pretty futile to begin with, and vice versa. If you want to catch a glimpse of Neptune while standing on Neso, the big gas planet would be barely visible as a disc — not quite the breathtaking blue-marble-rising-above-the-moon, one-for-the-ages shot the Apollo astronauts managed to capture on film. The sun, too, would just be a shiny dot in the sky above Neso, just bright enough to allow you to enjoy some vacation reading.
Popular with the scruffy backpacker crowd, Neso is not for you if you consider dependable public transportation or cushy rental cars non-negotiables. But here’s the good news: Because Neso is estimated to be a mere 40 miles or thereabouts in diameter, its gravity is low enough that you can hike – or rather, hop – around the whole thing in a day or so, and it would take you just a few hundred steps. They’d be big, slow and long steps, each lasting for about five minutes. Don’t worry about dropping your phone on Neso – it would take almost 30 seconds to make it to the ground, giving you plenty of time to catch it before having to check your travel selfies on a spiderwebbed screen.
While the starry night sky at the edge of the solar system likely is a sight to behold, stargazers should beware: the nightly lows on Neso spell serious trouble to the un(der)prepared. On Triton, another one of Neptune’s moons, temps go down to minus 391 degrees Fahrenheit, and while Triton holds the record as the solar system’s coldest object, Neso is unlikely to be any cozier. So be sure to bring some extra space blankets before heading out to stargaze.
Other useful items to carry on Neso include a quality flashlight, a healthy stockpile of batteries, boots with cleats to navigate rock-hard ice and pocket warmers (preferably the portable, nuclear generator kind because solar-powered devices won’t work this far out).
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