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NAU’s Ice Lab mixes up exotic ices from Titan

 A rim of ice crystals rings a round window with a blue backlight
Jennifer Hanley
Half methane, half propane ice forms in the chamber

It’s the middle of summer, but a science laboratory at Northern Arizona University is full of ice. Not just any ice, but bizarre kinds only found on faraway planets. KNAU’s Melissa Sevigny took a tour to see how scientists are making so called “exotic ices” that might exist in the outer reaches of the solar system.

 Two women look at a computer screen in a science laboratory filled with a complex-looking machine
Melissa Sevigny
Jennifer Hanley (standing) and Cece Thieberger examine results on the computer screen, next to the ice-making machine

This is not an ordinary icemaker. The machine in the middle of the NAU laboratory looks straight out of a science fiction novel. Tangles of tubes and wires lead to a small metal chamber in the center.

Jennifer Hanley is a researcher at Lowell Observatory.
"That sound is the coolant," she says of the constant humming. "That’s our helium compressor, and that’s basically what it sounds like when we’re running an experiment."

The experiment is making ice—the kind of ice you might find on Titan, the largest moon of Saturn.

"Titan is the only other planetary body that we know of that has stable liquids on its surface," Hanley explains. "But those liquids are not water like Earth. It is in fact mostly liquid methane."

Whole lakes and rivers of liquid methane, which can vaporize or freeze on Titan just like water does on Earth. Cece Thieberger, PhD student at NAU, says, "It's just so cool. I mean, there's an atmosphere on this moon. It rains on a moon!"

Humans have sent just one spacecraft to the surface of Titan—the Huygens probe, which transmitted data from the surface for an hour and a half. Another visit to Titan won’t happen for years. But scientists can create ice mixtures in this laboratory and study them without having to travel to outer space.

A row of large red and teal-colored canisters labeled with various gases
Melissa Sevigny
Canisters of methane, propane, nitrogen, and other gases wait to be mixed in the ice-making chamber

Thieberger demonstrates. "Behind you we have a bunch of scary look gas canisters that have all sorts of warning stickers on them," she says. She opens a valve and a hiss of propane gas whistles down a tube.

"We’ll open the gas canisters and put them into this part of our system, which is this Christmas tree looking setup," she explains.

Today’s mixture is half propane and half methane. Hanley says you can’t open the chamber to touch the forming ice, but: "We can look at it. We have windows which we can show you."

Droplets begin to form behind the circle of glass as the temperature in the chamber plunges. "Interesting," Hanley muses as the liquid begins to pool. "Do you see how it looks like there’s almost different densities as it cooling? There’s this a line in there, like a stratification."

The temperature drops to 70 Kelvin, or more than three hundred degrees below zero in Fahrenheit.

"Oh! I think it’s happening," Hanley exclaims as ice begins to form. "It’s really starting to go now."

 A round glass window shows forming ice backlit by a blue light
Melissa Sevigny
A tiny round window gives a glimpse of the ice making process.

The scientists will take spectra of the ice crystals—it’s a kind of chemical fingerprint. If future spacecraft return the same kind of spectra, Hanley says that’s a clue as to what kind of ice forms on other planets and how it behaves. Is it blobby or needle like? Does it float or sink?

"That’s another one of the things we’re trying to test," Hanley says. "Oh, wait, we might see ice floating on Titan? That is unexpected, but good to know, especially if we want to send a boat or submarine there, we need to watch out for icebergs."

Hanley and Thieberger say the dream to study these weird kinds of ice in their own environments, matching what’s found out in nature with the ice made in the lab.

"Spacecraft to all the planets, all at once," Hanley jokes.

"Spacecraft everywhere!" Thieberger chimes in.

"Instead of like one every ten years: all the planets, all at once, let’s do it."

Until then, the Ice Lab offers a tiny bit of solar system exploration right here on Earth.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.