Saturn's icy moon Titan is like an alternate-reality twin of Earth, with its fair share of mysteries. It's the only other world in our solar system dominated by organic molecules and decorated with lakes and rivers. It even has a dense atmosphere, seasonal weather and rainfall.
Even though it isn't precisely the same as our home -- its lakes are filled with methane and its rain would probably burn our skin -- Titan has proven a promising arena to seek out signs of extraterrestrial life.
NASA has plans to launch a rotorcraft, which it describes as a "large drone," to Titan in 2027 with the Dragonfly mission, hoping to locate something remarkable. But because it would take another seven years for NASA's craft to reach the planetary body -- it's nearly a billion miles away -- many researchers are working to understand Titan's environment down here on Earth.
A new experiment, by researchers at Southern Methodist University, aimed to do so by mimicking the conditions of Titan in a test tube. Titan seems alien, but it shares many organic molecules with our planet. But it's a much colder place.
"If we're going to study the minerals on Titan, we need to take a look at these common organic molecules ... but look at them with different eyes; look at them through the prism of Titan," explains Tomče Runčevski, an assistant professor at Southern Methodist University and principal investigator of the experiment presented at the fall meeting of the American Chemical Society.
Runčevski's "Titan-in-a-glass" aimed to do just that. The team combined features of Titan, such as its plunging temperatures and characteristic liquids, within glass cylinders. Then, they added two molecules, acetonitrile and propionitrile, present in the moon's atmosphere.
On Titan, these compounds are in the form of solid crystals that contain sequences of "polymorphs," or variations in structure, that are temperature dependent. The chemical composition is the same, but the way the chemicals bond is slightly different based on how hot or cold it is.
Mixing the molecules together produced a somewhat surprising result.
When the researchers ran their "Titan-in-a-glass" experiment, the structural sequences of these two molecules changed, with both high and low temperature polymorphs stabilizing. The compounds' properties were adjusted, too.
"This is very interesting and important, because so far … all the studies that have been done for acetonitrile -- and there are a lot of studies -- they assume that they will have the low temperature polymorph, because on Titan, the temperature is low."
Titan boasts freezing temperatures dropping down to -290 degrees Fahrenheit. But that didn't stop high temperature polymorphs from forming. The result shows it's not just temperature affecting Titan's chemistry.
"On Titan, we cannot assume that these molecules will be alone," Runčevski said. "Titan is a world. The chances that one might encounter these molecules in the form that we propose, it will be decent."
Strikingly, the newfound properties of acetonitrile and propionitrile may also address many long-standing questions of Earth-based chemistry, too.
"On Earth conditions, those chemicals are liquid, so no one 'cares' what their solid might look like. And now because of Titan, this type of research got revitalized and people again started looking at those fundamental questions," Runčevski remarked, adding that "the fact that now, in the 21st century, we're still discovering things about the most common organic solvents and fuels on Earth is fascinating."
The team aims to check their results against the spectroscopic data collected by NASA's Cassini-Huygens mission, which sent a probe to tour Saturn and its moons between 1997 and 2017.