Visualization of sample return launch from Titan.
Titan is weird. The only known moon with an atmosphere, Saturn’s largest moon has rain, lakes, oceans and ice comprised not of water, but of liquid ethane and methane. It’s chemistry is therefore complex, but also combustible. Could NASA send a spacecraft to scoop-up a sample and return to Earth, using Titan’s freely available methane as propellant?
If it could, that mission could bring home to scientists a compound that could hold the secret of how life emerged in the early Solar System.
That’s exactly what NASA’s Steve Oleson and Geoff Landis are working on at the space mission-designing Compass Lab at NASA Glenn Research Center in Cleveland, Ohio. Part of the NASA Innovative Advanced Concepts (NIAC) program, the Titan Sample Return Using In-Situ Propellants project is being studied as a possible successor to an already planned mission to the bizarre Saturnian moon.
NASA’s Dragonfly—a kind of drone—will launch in 2025 and reach Titan in 2034 to study Titan’s prebiotic chemistry for almost three years.
The Titan Sample Return will build on that—and do something quite incredible:
Why is Titan so interesting?
“Titan is just absolutely fascinating in almost all possible ways,” said Geoff Landis, the science lead investigator for Compass Lab. With Oleson he’s previously worked on a Titan Submarine, to explore its lakes and a a hopper for exploring Neptune’s moon Triton. “It’s the only other world in the Solar System that has weather and liquid on the surface. It's Earth and Titan that have lakes and seas and rain—and that’s it! Except that on Titan it’s not liquid water.”
Why do we need a sample return from Titan?
Most fascinating about Titan is the organics on its surface. “Look at the surface and you see this muddy reddish color—that’s organic compounds called tholins,” said Landis.
The word “tholins” was coined by iconic astronomer Carl Sagan to explain what happens when organic materials, including hydrocarbons but also phosphorus and sulfur, are exposed to radiation and sunlight for a long period of time.
During NASA's Cassini mission's final distant encounter with Saturn's giant moon Titan, the ... [+]
What are ‘tholins?’
Tholins are the complicated organic molecules that result from that process—and we know almost nothing about them. “There’s a lot of thinking that these sort of molecules are the building blocks from which life started because they must have been present in the early Solar System,” said Landis.
Tholins don’t don't exist any closer than the outer Solar System—that’s at Saturn and further out—but they may have been present on the early Earth. “If tholins are the basis for the formation of life, we want to go to Titan essentially to find out where we come from,” said Landis.
How would a sample return mission land on Titan?
“We expect the landing on Titan to be relatively easy,” said Steven Oleson, lead of the Compass Lab and principal investigator for this study. “Titan has a thick atmosphere of nitrogen—1.5 times the atmospheric pressure of Earth—which can slow the lander’s velocity with an aeroshell and a parachute for a soft landing, just like astronauts returning to Earth.”
Unlike Mars landers, a mission to Titan does not need a final rocket-powered descent stage.
The importance of Dragonfly
“Dragonfly is our scout,” said Oleson. “Detailed images from Dragonfly will tell us everything we need to get ready.” Their sample return mission would require a rover or a Dragonfly-like drone to identify compounds to bring home, but by then that would all be using existing tried-and-tested technology.
“Once Dragonfly has demonstrated mobility on Titan we’ll have a vehicle that can fly around finding samples,” said Landis. “The next step is to use a Dragonfly-like vehicle to pick up samples and bring them to our our sample return vehicle.”
Saturn's moon, Titan, in ultraviolet and infrared wavelengths. The Cassini spacecraft took the image ... [+]
How could propellant be sourced on Titan?
The really clever part of the concept is the production of fuel on Titan itself, allowing a sample-return platform to be just a fifth of the mass compared to one that had to take its own fuel along.
Luckily, Titan is the perfect place to source and process propellant without complicated chemical processing. After all, there are lakes full of liquid methane and ethane. “We could use a hose and pump up the liquid from a lake,” said Oleson. Easy!
Meanwhile, liquid oxygen—which would be needed for the fuel to burn—could be produced by melting the hard frozen pieces of water-ice on Titan’s surface, as seen by the Cassini-Huygens probe back in 2005. “A reactor on the surface could grab that and heat it up and use electrolysis to make liquid oxygen and hydrogen,” said Oleson. Storage wouldn’t be a problem, either. “On Titan it’s only a few degrees above liquid nitrogen temperatures, so very easy to keep that cold.”
Oleson and Landis reckon that the small amount of technology development required—chiefly the electrolysis part—could be completed within a decade.
When will the mission launch how long will it take to get to Titan?
This mission would last about 14 years. It would take roughly seven years to get there, and then the same to get back, though well-timed gravity-assists either on the way there or back could reduce the total flight time to just 10 years.
When to go is tricker—though certainly it would go after Dragonfly has landed and returned data. “When you go is also going to tell you where you go because Titan has seasons that last about seven years—but we want good lighting,” said Geoff. “Orbital mechanics will tell you when is a good time to go to Titan and once that’s decided it will give us a band of where we can land on Titan.”
Jupiter's moon Europa, as seen in this image taken June 27, 1996 by NASA's Galileo spacecraft. ... [+]
Is Titan more interesting than Europa?
It’s way more accessible—and could be just as interesting. “Europa is the big target because we think there's an underground ocean, but it’s below so many kilometers of ice,” said Oleson. “On Titan everything is so accessible—you could get a submarine and splash down into its lakes [another idea of Oleson and Landis], you can fly around with Dragonfly, and it’s got organic compounds you could get a sample of.”
On Europa is aqueous chemistry—the chemistry of us. However, Titan could tell us something about the building blocks that may have been the origin of life. “As far as an accessible world that’s most like Earth and has organics, Titan really is the place to go,” said Oleson.
Wishing you clear skies and wide eyes.
