Titan sample return
A new NASA Institute of Advanced Concepts study is looking at the surprising advantages of a mission to Saturn’s moon
A new NASA Institute of Advanced Concepts study is looking at the surprising advantages of a Titan sample return
We’ve launched missions across the Solar System and studied an increasing number of diverse targets, from gas giants to asteroids. But so far we’ve only brought physical samples back from the Moon and a couple of asteroids, with a Mars sample return a long-held ambition for NASA. However, Titan has such good resource options it may make sample return surprisingly easy for such a distant target.
Titan is arguably the most interesting target in the Solar System. It’s the tenth-largest body and has a dense atmosphere of mostly nitrogen and methane. A similar effect that makes the surface pressure of Venus crushingly high gives this small body an atmospheric pressure just slightly greater than Earth’s, making it the only surface beyond Earth where you wouldn’t need a spacesuit. The other thing this dense, cold atmosphere enables is a surface liquid cycle, giving Titan rain, rivers, lakes and seas like we see on our home planet, but rather than water they are methane.
Though not expected to have surface life, it’s an example of a prebiotic planetary surface, deep frozen for posterity. Titan also has a subsurface water ocean, which like Europa and Enceladus offers the possibility of harbouring simple life in the depths. But it’s not an easy place to reach. Pioneer 11 and Voyagers 1 and 2 have performed Saturn flybys, and the Cassini orbiter spent 13 years in orbit after a journey of almost seven years. Cassini also brought the Huygens lander, which touched down on Titan in January 2005.
But despite the distance, Titan has a selection of attributes which could make sample return surprisingly feasible, starting with landings. This year saw NASA perform another dramatic crane landing with Perseverance. NASA is forced to employ such a complex system because Mars has a thin atmosphere. It’s enough to get in the way and generate entry heating, but not thick enough to significantly slow spacecraft down. Titan’s thick atmosphere would enable a lander to shed orbital speed through atmospheric drag and make a soft landing with a parachute.
All this serves to reduce the mass that must be taken to Titan in the first place, but it’s with propellant supply that Titan really shines. On Mars methane must be formed out of the atmosphere, but on Titan rocket fuel is actually falling from the sky and lying around in pools, ready to be pumped into fuel tanks.
For oxygen, water ice doesn’t need to be carefully filtered from the soil, as it constitutes the whole planetary crust. A prospective mission could melt the ice with waste heat from a radioisotope thermoelectric generator before splitting it into hydrogen and oxygen, releasing the hydrogen and storing up the oxygen.
On Titan oxygen and methane can even be stored as liquids without refrigeration. When it comes to launching home, potentially with samples collected by NASA’s nuclear-powered Titan quadcopter Dragonfly, the surface gravity is only 14 per cent of Earth’s, making access to space somewhat easier. It may be some time before Titan samples are coasting back to Earth, but it could be sooner than you might think.
1 Saturn
Titan is the largest moon of Saturn, and the iconic Ringed Planet will loom large – clouds permitting – in Titan’s sky.
2 methane lakes
Titan’s unique advantage is that methane exists on Titan as water does on Earth, so there are huge reserves of liquid methane handy for filling tanks.
3 Water ice
While methane takes the place of water on Titan, water ice takes the place of rock. The crust is formed of ice, which can be melted and split to produce oxygen.
4 Dense atmosphere
Titan’s atmosphere is made up of nitrogen, giving the small body slightly more surface pressure than Earth. Combined with low gravity, this makes Titan good for aerobraking and parachute landings.
5 Dragonfly mission
NASA is also working on the Dragonfly mission for Titan, a nuclearpowered drone to explore the surface. This could bring samples to a samplereturn mission.
6 Samplereturn launch pad
The mission will likely consist of a lander, which will take care of the descent and resource collection before serving as the launch pad.
7 Lowtemperature storage
Titan’s lowtemperature and highpressure environment means both methane and oxygen can be stored at ambient temperatures without refrigeration.
8 Samplereturn vehicle
Samples would be loaded into an aerodynamically shaped launcher to cope with Titan’s atmospheric drag, despite its low gravity.