Forget a boring old rover and try nuclear-powered boats or quadcopter space drones. If we want to explore Saturn's moon Titan — with its liquid methane lakes and dense nitrogen atmosphere — we'll need exploration schemes that are just as unique as the alien moon itself.
To date, manmade crafts have usually landed on celestial bodies with entirely solid surfaces or thin or non-existent atmospheres. (The moon, Mars, and Rosetta's comet to name a few.) For that, a rugged rover is fine. But Titan is otherworldly body in our solar system with stable liquid lakes and oceans, which call for underwater (undermethane?) explorers. That, and its dense atmosphere supports swooping aircraft more easily than on our home planet.
In 2005, the European Space Agency landed the Huygens space probe on Titan. The little round probe was designed to sit at its touch-down site and transmit data for just over an hour before bidding a final farewell. Since then, we've learned a lot more about Titan, and the proposed probes for exploring it have grown ever more extravagant.
Just last week, NASA unveiled a robotic submarine to explore Titan's methane seas. Let us take a look at some of the other fascinating ideas that space scientists have dreamed up for Titan.
A Hot Air Balloon That Circumnavigates the Moon
The closest we actually have to a plan for exploring is the joint NASA/ESA Titan Saturn System Mission, which is supposed to launch in 2020 and arrive in 2029. If it ever gets funded, but that's a whole other story. The TSSM is 3-in-1 plan that includes an orbiter and two exploration probes: a hot air ballon and a lake-lander. Let's tackle the hot air balloon first.
With atmosphere thicker than Earth's but gravity only 1/7th as strong, Titan makes it much easier to stay aloft. (In fact, it's been suggested that even humans could take off while wearing wingsuits if they were on Titan.) Since it's also a frigid -290 Fahrenheit on the moon, it takes only 1 per cent of the heat it would need on to fly on Earth. Titan's trade winds could allow the balloon to circumnavigate it, providing a close-up aerial view of the moon's terrain.
A Nuclear-Powered Boat
With a balloon for the air, the second half of TSSM's exploration plan is focused on the seas. The Titan Mare Explorer (TiME) would parachute down into one of the large lakes that dominate the moon's northern pole. The most likely candidate is the Ligeia Mare, a body of liquid hydrocarbons like methane, ethane, and propane that is larger than Lake Superior. TiME would be the first floating vehicle to ever explore an alien sea.
Titan's winds would push the boat along the surface of the lake as it analyses the moon's methane cycle, which is analogous to Earth's water cycle. But the boat would still need a power source to navigate and run its instruments. Since the atmosphere of Titan is too hazy for solar panels, it would to be powered by nuclear energy.
Small Quadcopter Drones
We've already extolled the virtues of the hot air balloon on Titan, but balloons are not nimble; they are not good at landing and taking off. But you know what could be good at all that? Drones.
To that end, NASA JPL scientist Larry Matthies has proposed studying small 10-kilo drones that deploy from a mothership like a balloon or a lander. The drones could, "acquire close-up, high resolution imagery and mapping data of the surface, land at multiple locations to acquire microscopic imagery and samples of solid and liquid material, return the samples to the mothership for analysis, and recharge from an RTG on the mothership to enable multiple sorties". Small drones get ever more useful for flying on Earth, and that technology could one day also help us explore Titan.
A Big Non-Quadcopter Drone
Image by Mike Malaska
So maybe a hot air balloon and quadcopters is too much. Maybe we just need a vehicle that is a compromise between the two. That would be AVIATR, or the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance, proposed by University of Idaho physicist Jason Barnes in 2012.
AVIATR is a 113-kilo plane that would soar through Titan's atmosphere with a nuclear power source that lasts for a year. Barnes also proposed a novel "gravity battery" idea, where AVIATR could climb to high altitudes to store energy and then cut off power to its propeller and glide. During that time, its power can be focused on sending data back to Earth. Of course, this is only possible because of Titan's dense atmosphere and low gravity.
Titan's largest and northern most body of liquid is the Kraken Mare, 150,000 square miles of what we believe to be mostly liquid methane. Based on measurements from Cassini, the probe orbiting Saturn, scientists believe the Kraken Mare could be over 150 miles deep.
In a proposal unveiled last week, NASA envisions sending a Titan submarine in 2040, some time after the Titan Saturn Mission System has already explored the moon's surface. The sub would be equipped with instruments to study tides, currents, chemical composition, underwater features, and whatever weird life might lurk below. I mean, with a name like Kraken Mare...
Along with its proposal for the submarine, NASA released this video with beautiful artist renditions of Titan's glittering methane seas. The music is stirring, but it obscures the fact that a Titan mission is not high on NASA's current agenda. Hopefully, mankind, or at least its robotic probes, will make out there. Because not only are there fascinating things to discover, there are also fascinating ways to discover them.
All image via NASA unless otherwise credited.