If you’re looking for a scenic lakeside destination for your summer vacation, you have two options: Earth, and a moon of Saturn called Titan.
These are the only two places in the solar system with bodies of liquid on the surface. Like Earth, Titan has an atmosphere, weather, and a natural cycle in which drops fall from puffy clouds onto the surface, before evaporating back up to start again. But the “rain” isn’t water; it’s methane, which exists as a liquid on Titan.
Scientists suspected that Titan had lakes years before they sent a spacecraft to check it out. The nature of Titan’s intriguing atmosphere suggested that it might deposit droplets to fill streams, lakes, and entire oceans. When Cassini, the now-defunct NASA spacecraft, arrived at Saturn in 2004, it turned toward Titan, the largest of the planet’s moons. The spacecraft’s radar instrument, permeating the haze, detected a very smooth surface, with narrow shapes at its edges that spread like capillaries from a vein. Another instrument absorbed the little bit of sunlight reflected from this mysterious surface and analyzed it. “It looked exactly like afternoon light reflecting off lake waters on Earth,” according to Amanda Hendrix and Charles Wohlforth, the authors of Beyond Earth: Our Path to a New Home in the Planets.
Like water on Earth, the methane has slowly etched canyons into the landscape and filled them with lakes. Lakes that, perhaps someday, human beings might visit for a little R&R, hundreds of millions of miles away.
It’s unlikely, but summer, arguably the best season for daydreaming, is upon us, so I reached out to a few scientists who study Titan to gauge the moon’s qualifications for a cosmic getaway. Set aside the long and dangerous journey, which would require astronomical leaps in technology if you planned to leave tomorrow. What might it be like to stand on the shores of a Titanian lake and look out across the expanse?
Well, you wouldn’t be able to see much, actually. Our dinky human eyes weren’t made for Titan, which is covered in thick haze, tinted the color of Dijon mustard because of chemical interactions between sunlight and compounds in the moon’s atmosphere. Unlike on Earth, sunlight strains to break through to the surface.
“Our vision is adapted to the situation on Earth—a lot of visible light,” says Daniel Cordier, a scientist at the University of Reims in France. “On Titan, only a tiny fraction of visible light entering the atmosphere reaches the ground.”
To get a better look, vacationers would need high-tech sunglasses designed to see in other forms of light, like infrared. You wouldn’t need to pack sunscreen; the sun appears 10 times smaller on Titan than it does here on Earth.
You wouldn’t need a spacesuit either, which sounds inconceivable, considering that every person who has ever left the comfort of Earth’s atmosphere has had to wear protective material to prevent a swift death. But air on Titan is dense enough to allow people to walk around without pressurized spacesuits, free from bulky, constricting garments and the danger of their bodily fluids boiling. By this measure, Titan isn’t as inhospitable as other worlds in the solar system, like our own moon or Mars.
No stepping outside without an oxygen mask, though: Titan’s atmosphere is made of about 95 percent nitrogen. You’d also need the right clothes to contend with the temperature. This moon’s fleece of an atmosphere keeps the surface temperature about the same day after day, changing only by a degree or two. This might sound pleasant, but that temperature is about –292 degrees Fahrenheit (–180 degrees Celsius). Visitors would need garments layered with insulation or designed to generate heat for its wearers.
Let’s say you’ve chosen a Titan lake called Ligeia Mare as your holiday spot. Ligeia Mare is about the combined size of two Great Lakes, Huron and Michigan, but looks nothing like them. The surface is smooth, nearly textureless. There are no big waves, no whitecaps at their shifting peaks. When Cyril Grima, a scientist at the University of Texas, imagines himself there, he looks down at his feet and spots a block of ice the size of his fist. He thinks about throwing it out into the lake; at these temperatures, water on Titan exists only as ice and litters the surface like rocks. But he wouldn’t want to disturb the eerie tranquility of the alien lake. “You don’t want to break this quiet liquid body, as peaceful as pristine snow before being lacerated by footprints,” Grima says.
Scientists are still trying to explain the uncanny smoothness of Titan lakes. The Huygens probe, a little spacecraft Cassini dropped on the moon in 2005, was designed to float and measure the size of waves in the predicted bodies of water. But Huygens landed on solid ground and exhausted its batteries in less than three hours. The probe’s cameras captured and sent home mesmerizing photos of the terrain, including gullies, winding ravines chiseled into the landscape by flowing liquid. What scientists know about Titan’s liquid features, they glean from data collected by Cassini, which ended its mission in 2017, and telescopes here on the ground or in orbit around Earth.
According to Cassini data, most waves reach only about a centimeter in height, a fraction of an inch. This seemed unusual to scientists, who had seen, in other data, plenty of evidence of wind, including dunes. Gusts generate some patches of ripples, particularly in the spring and summer seasons, but no undulating patterns, like that of terrestrial lakes. Cordier suspects that something on the surface of the lakes is dampening potential ripples. One potential culprit, he says, are organic particles formed in the atmosphere that float down to the surface. The particles, known as aerosols, might not like mixing with water, and so they settle over the lakes like oil. They might also be less dense than liquid methane, so they simply float on top in a layer, muffling the waves.
Swimming is probably out of the question, not without the right, technologically advanced attire. If you made it in, the act would feel unnatural and difficult. Liquid methane is about half as dense as water, which means swimmers would have to exert more effort to keep themselves from sinking.
And watch out for bubbles rising from below. Titan’s lakes are made of a swirling mixture of methane, ethane, and small amounts of nitrogen. The methane-rich liquid at the surface flows downward into the depths, toward ethane-rich liquids. The movement jostles nitrogen, and it ascends to the surface and fizzes. “Methane and nitrogen mix better than ethane and nitrogen, so once you get rid of some of the methane, nitrogen is like, ‘Meh, I’d rather not stick around with you, ethane. I’m going to peace out and go back to the atmosphere,’” says Shannon MacKenzie, a planetary scientist at Johns Hopkins Applied Physics Laboratory.
In the midst of all that nitrogen fizz, keep an eye out for something even more startling: life. No life-forms have been detected on Titan, but scientists say the moon might provide the conditions for it. Telescope observations have detected a compound coursing through the atmosphere that could interact with the methane and ethane to create cell-like membranes.
Getting around on foot would be far easier than on Earth. Titan has even less gravity than our own moon. Vacationers could bounce around as the Apollo astronauts once did, decades ago. They could even, as Hendrix and Wohlforth suggest in their book, flap around in winged suits to “effortlessly glide great distances.” Falling would not be perilous; objects take longer to descend in such a thick atmosphere. (Scientists with multimedia skills: Please simulate someone executing a perfect cannonball off a diving board and into Ligeia Mare.)
The appeal of a lake vacation is not just the water itself. These spots are usually low on light pollution, providing more unfiltered views of the night sky. But under Titan’s opaque skies, the stars and other planets wouldn’t be visible. Neither would the sight that might draw tourists to the moon, which has dazzled humans from afar for centuries: Saturn’s rings. For starry views, it might be best to stay on Earth.