Hundreds of millions of miles away, in the orbit of Saturn, on the surface of Titan, the planet’s largest moon, rests a piece of human-made technology. Huygens, a nine-foot-wide, saucer-shaped probe, was dropped by the passing Cassini spacecraft and parachuted down to the surface in 2005. For a precious 72 minutes after it landed, Huygens transmitted data back to Earth, including image after image of its surroundings. There they were—gullies, the kind that on Earth are etched into rocky terrain by flowing water. Scientists watched, enthralled, as views of an alien land flashed across computer screens, marking humanity’s first look at the surface of a moon that wasn’t their own.
Then Huygens, out of battery power, went dead; its demise was, as grim as it seems, part of the plan. Huygens remains in the spot where it landed, a dusty monument to the desire to glimpse, even briefly, the worlds in our solar system.
But a new piece of technology may be on its way. Not to land on Titan, but to hover—getting just close enough to reveal secrets.
A mission to send a drone-like spacecraft to study Titan received approval and funding from NASA Wednesday. Dragonfly, a dual-quadcopter, would launch in the mid-2020s and, upon arrival, hop from one spot over Titan’s surface to the next, searching for signs of life.
The funding comes from NASA’s New Frontiers program, a competition for exploration proposals that has produced several well-known and successful robotic missions in the solar system: New Horizons, which flew past Pluto in 2015; Juno, which currently orbits Jupiter; and OSIRIS-REx, which is on its way to an asteroid called Bennu, where it will carve out some surface material and return the sample back to Earth. The Dragonfly mission, led by Elizabeth Turtle, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory, now has $4 million and one year to complete its concept. So does the second mission NASA approved today, the Comet Astrobiology Exploration Sample Return (CAESAR) that would target a comet that approaches the sun about every six-and-a-half years. But only one of these missions will actually launch—NASA will choose between them in 2019.
Titan, the largest of Saturn’s moons, has long mystified scientists. The moon is wrapped in a dense, planetlike atmosphere mostly made of nitrogen. Spacecraft like Voyager 1 and Cassini have detected a plethora of complex and organic molecules in the atmosphere that are also found on Earth. Robotic missions have also revealed Titan has a similar liquid process to the water cycle on Earth, but with a different chemical compound: methane, the main ingredient of natural gas. On Titan, methane clouds release methane rains that feed methane lakes and seas and streams that can erode the rocky landscapes. This makes Titan, like Earth, an ocean world. All together, these features mean Titan is one of the best candidates for life in our solar system.
But, aside from Huygens, the imaging instruments on spacecraft that have visited Saturn’s orbit have been unable to penetrate Titan’s hazy atmosphere, and the composition of its surface remains largely unknown.
Dragonfly, should it take flight, will carry equipment capable of identifying chemical components important to biological processes. It will search for signatures of hydrocarbon-based life-forms and water and check for signs of progress in prebiotic chemistry—the transformation of simple molecules into complex life. It will carry cameras that will help the copter choose future landing sites and, of course, send home potentially beautiful, high-resolution images. “We’re not exactly looking for five-legged creatures running around or something like that,” Peter Bedini, the program manager for Dragonfly, said during a talk in July. “Although if we did confront one of those, we’d be sure to take a selfie and send it home.”
The support for the Dragonfly mission is a boon to astrobiologists seeking signs of life on other ocean worlds, like Enceladus, another Saturnian moon, and Europa, a moon of Jupiter. On these moons, potential oceans lurk under thick crusts of ice, perhaps teeming with microbes and other life-forms.
The drone-like design of Dragonfly is unusual given the previous roster of robots sent to explore the solar system, like the suite of landers and rovers that have traveled to Mars since the 1970s. But “the dense, calm atmosphere and low gravity [of Titan] make flying an ideal means to travel to different areas of the moon,” the Dragonfly team explains. Aerial probes can cover more ground than rovers. Mars rovers like Curiosity and Opportunity have a top speed of less than one mile per hour, and are not built to maneuver over particularly rough terrain. After five years on Mars, Curiosity’s wheels show some significant damage from crunching over rock. As NASA pushes forward with the exploration of worlds whose surfaces are less understood than that of Mars, scientists and engineers may need to rethink the hardware best suited for exploration.
“In just a few flights, Dragonfly will be able to go farther than the Opportunity rover on Mars has in the last 12 years,” Bedini said.