NASA has announced that it will launch a space probe called Dragonfly on an ambitious mission to Saturn's moon Titan, in which a robotic rotorcraft-lander will fly around Titan's surface and touch down in various places. As part of its exploratory mission, the Dragonfly space probe will look for traces of chemical processes similar to the ones that led to life on Earth, in addition to gathering other information about the moon's surface and atmosphere.
Dragonfly will launch in 2026 and arrive at Titan, which is 886 million miles (1.4 billion kilometers) from the sun, in 2034. Once it's there, the space probe — which is about the size of the space agency's Spirit and Opportunity Mars rovers — will turn on its eight rotors and fly through Titan's dense, hazy atmosphere, which is about four times the density of Earth's, and explore its still-mysterious surface.
Titan, the biggest of Saturn's 62 moons and a close second in size in our solar system next to Jupiter's moon Ganymede, has a radius of about 1,600 miles (2,475 kilometers), making it about 50 percent wider than Earth's moon. But it's not just Titan's size that has made it a longtime object of fascination to scientists.
Titan also is the only moon in the solar system with much of an atmosphere, and it's the only slot in the solar system besides Earth that's known to have liquid rivers, lakes and seas on its surface. Though the latter are made up of liquid hydrocarbons such as methane and ethane, Titan also is believed to have an underground ocean of water 35 to 50 miles (55 to 80 kilometers) beneath its icy surface that possibly have harbored some form of life, or may still contain it. If life exists there, it would have be extremely hardy to survive in Titan's brutally cold surface temperature of minus 290 degrees Fahrenheit (minus 179 degrees Celsius).
Titan's thick atmosphere is about 95 percent nitrogen, with the rest mostly composed of methane. That creates a thick, orange-colored haze that hangs over the moon's surface, making it difficult to observe from Earth. Much of what we do know comes from the European Space Agency's Huygens spacecraft, which landed on Titan and transmitted data for 72 minutes in 2005, and from NASA's Cassini probe, which did multiple flybys of Titan between 2005 and 2017. (Huygens actually was attached to Cassini for the seven-year trip to Titan's vicinity.)
"It is hard to imagine a more exciting scientific mission than a nuclear-powered helicopter on a voyage of up to eight years of exploration of a new world," says Dale Skran, chair of the executive committee for the National Space Society, a nonprofit organization that advocates the exploration and colonization of space.
Dragonfly's Flight Advantage
Scientists are particularly excited about Dragonfly's ability to fly rather than crawl along on the ground. Unlike Mars, where NASA also plans to test a small robotic helicopter with large, high-speed blades in 2020, Titan's atmosphere is thick enough to enable Dragonfly to attain lift with relatively small rotors, and able to carry a bigger payload over longer distances than the experimental copter being sent to Mars. It's expected to cover more than 108 miles (175 kilometers) during its nearly three-year mission on Titan. It will fly in short hops of up to five minutes at a time.
"Flight allows us to move the lander much greater distances in a short period of time than a traditional rover, allowing us to more efficiently explore Titan," Jason Soderblom, a research scientist in the Department of Earth, Atmospheric and Planetary Sciences at Massachusetts Institute of Technology and one of Dragonfly's co-investigators, explains in an email.
Curt Niebur, New Frontiers program scientist for NASA, explains via email that Dragonfly's design is fundamentally different from the Mars Helicopter. "Not just because the atmosphere of Titan and Mars are so different, but because they are different vehicles," he says. "The Mars Helicopter is a short-lived technology demonstration with no science payload. Dragonfly is a self-contained spacecraft designed to pursue a science mission with high autonomy. It's like comparing a self-driving car and an electric scooter: both have wheels, but they have very different purposes and therefore very different designs."
The Geology of Titan
The researchers working on Dragonfly are excited about the opportunity to investigate the giant moon's many mysteries. "I am looking forward to Dragonfly finally giving us detailed answers about the surface of Titan at the small scale. Not just its composition but also its geology," Neibur explains. "Telling us about the complex organic materials present there, and how they interact, and also giving us a good look at surface features like dunes and the Selk Crater. Cassini did a good job at giving us broad answers to this question at the large scale (tens of miles, for example), but nothing beats getting down to the surface and actually digging your hands and feet in, so to speak."
"There is a plethora of unanswered questions about Titan's surface," Soderblom says. "One fundamental question we have yet to answer is what is the composition of Titan's major geologic units, or if the water-ice bedrock is exposed anywhere on Titan or if it has been buried beneath organic gunk. This is because Titan's atmosphere obscures the surface at most wavelengths, limiting our ability to use traditional remote sensing techniques to study the surface composition."
Dragonfly's scrutiny of Titan's surface may also yield insights about the moon's atmosphere. "The organics on Titan's surface are all made in the atmosphere," explains Sarah Horst, an assistant professor in the School of Earth and Planetary Sciences at Johns Hopkins University, who also is an investigator on the project. "So understanding the composition of the complex organics we find on the surface will allow us to dramatically improve our understanding not just of the processes that happen on the surface, but also the chemistry that is occurring in the atmosphere," she says.
"That, in turn, is important for understanding the role that atmospheres may play in the origin or evolution of life and also help us figure out what types of molecules may constitute evidence for life when we are looking at observations of faraway atmospheres like those of exoplanets," Horst says.