Human exploration of planets and moons in the solar system has thus far taken place on dry land, thanks largely to the lack of liquid water on most celestial bodies. The NASA Innovative Advanced Concepts program has developed a concept for a robotic submersible vehicle for planetary exploration, but it won’t be deployed in water. The aptly (though unimaginatively) named Titan Submarine Phase I Conceptual Design could some day go for a dip in the hydrocarbon lakes of Saturn’s moon Titan. 
 
 Titan has always been an interesting target for study because it’s so unusual for a moon. It’s larger than Mercury and has an atmosphere one-and-a-half times as dense as Earth’s. The atmosphere is mostly nitrogen and methane with hints of hydrogen, so certainly nothing that would support life as we know it. Titan’s temperature can reach a positively frigid -179 degrees Celsius (-290 degrees Fahrenheit). These super-low temperatures and thick atmosphere combine to create the feature scientists are so anxious to study in detail — vast lakes and rivers of liquid methane and ethane. 
 
 Data from the Voyager, Cassini, and Huygens (deployed by Cassini) probes have confirmed that there are three large polar seas on Titan’s surface, and the largest of them is known as Kraken Mare. This is the target for NASA’s Titan submarine as it would provide the most opportunities for exploration. 
 
 The conditions in Kraken Mare would be challenging to say the least. The massive hydrocarbon lake has an area of 400,000 sq km (154,000 sq miles) and is believed to be as much as 160 meters (525 feet) deep. There are also currents and tides to deal with, and it’s not like mission control could just nudge the submersible this way or that whenever it needed. Titan is about 80 light minutes away, so that means NASA would have to wait 160 minutes to get a response after each command was sent. Real time control is out of the question. 
 
 NASA engineers estimate the Titan Submarine would weigh in at about one ton and make use of electrically-powered turbines to get around the liquid methane lake. Titan is far from the Sun, making solar power inefficient, and the sub would spend most of its time beneath the surface where solar panels wouldn’t work anyway. Like many deep space probes, the sub would rely on a radiothermal Stirling generator to produce about 1kW of power. The concept submersible could reach speeds of about one meter per second, according to NASA. 
 
 There aren’t many details on exactly what sort of instruments the Titan sub would carry, but the data obtained would be transmitted back to Earth in an unusual way. Rather than introduce the complication of an orbital component to act as a link with NASA, the sub itself would have a large dorsal fin with a built-in planar phased-array antenna. It would surface for 16 hours per day to beam data back before sinking once more beneath the methane waves. Surfacing and diving will be controlled with ballast tanks, just like an Earth-bound sub, but the details have yet to be worked out. Methane and ethane don’t work quite like water, and there’s concern nitrogen gas could condense in the tanks, dropping the sub to the bottom of Kraken Mare. 
 
 This is still just an early concept of a possible future mission. NASA estimates some descendant of the Titan Submarine Phase I Conceptual Design could reach Titan around 2040, but there’s a lot of work to do before then. 
 
 Now read: A tribute to Cassini: 10 years spent revealing the secrets of Saturn and its moons ||||| Video screenshot by Eric Mack/CNET 
 
 I think we can now officially say that NASA's real-life mission concepts have met, if not exceeded, the wildest dreams of Jules Verne and the other early futurists. Verne saw us flying around the world, traveling to the center of the Earth (not a great idea, it turns out) and to the moon, but I bet he never imagined that just 110 years after his death, we'd be working on a robot submarine to probe the flammable seas of a distant world. 
 
 Truth can be stranger than fiction, indeed. 
 
 Earlier this month, NASA published the below video introducing its concept submarine designed to explore Kraken Mare, one of the methane seas on Titan, the remarkably strange moon circling Saturn. Even if it were possible for humans to go swimming in Titan's seas, it might not be advisable. It would be something like swimming in a freezing ocean of liquefied natural gas. 
 
 Clearly, this is a mission meant for a drone, specifically a nuclear-powered, single-ton robotic submarine equipped with a seafloor camera and sampling system as described in a brief (PDF) on the concept posted online. 
 
 Getting the sub to Titan presents a bit of challenge since it won't fit into the sphere-cone shaped landers that have typically been used for planetary exploration in the past. However, it could fit into a space plane like Boeing's X-37, which was recently orbiting the Earth for some sort of classified, likely spy-ish US Air Force mission. The space plane would make a soft water landing on Kraken Mare and jettison the sub, or possibly drop it at low altitude via a parachute. 
 
 In addition to floating or diving around checking out the chemistry of Titan's sea and sea floor composition, the sub could also study the moon's tides, weather, shoreline, disappearing islands and keep an eye out for any evidence of really weird life forms that like to hang out in super chilly, gassy locales. 
 
 The Titan sub concept is very preliminary at this point, but there's plenty of time to work on it. The team behind it anticipates that it might not splashdown until sometime around 2047.
– Saturn's moon Titan, which happens to be larger than the planet Mercury, is cold. Very cold. As in -290 degrees Fahrenheit is not out of the ordinary. These super low temps, combined with an atmosphere roughly 1.5 times as dense as Earth's, have resulted in a few extraordinary bodies of liquid methane and ethane, reports Extreme Tech, and scientists are anxious to explore their depths. (In fact, Titan is the only body aside from Earth to boast liquid lakes on its surface.) So NASA is working up a (very early) model of a submarine drone that could do just that—one that CNET reports will likely be nuclear-powered, weigh a ton, and come equipped with a seafloor camera, sampling system, and other fancy futuristic robotic accoutrements. But don't get too excited just yet. First, this is a fully automated mission: "Even if it were possible for humans to go swimming in Titan's seas," notes CNET, it "would be something like swimming in a freezing ocean of liquefied natural gas." Hence, NASA's goal of sending the "highly capable science craft" to Titan's largest sea, Kraken Mare, around the year 2040, in what it calls "an unprecedented planetary exploration mission." Many details remain to be sorted out, including how to get the craft to Titan (Boeing's X-37 is a possibility), how to land it (parachute drop), and while there, how to communicate with Earthlings (planar phased-array antenna). (Something else on Titan has been stumping NASA.)