NASA has selected two missions to further explore past targets—Saturn's largest moon, Titan, and the comet 67P/Churyumov-Gerasimenko—as the final candidates for its next billion-dollar robotic spacecraft, the agency announced today. The candidates for the next New Frontiers mission, chosen from a field of 12, will now have until January 2019 to refine their pitches to the agency, with a launch planned by 2025.
The first, Dragonfly, would send a semiautonomous quad-copter to fly between sites on the surface of Titan, which features an Earth-like landscape of rivers and lakes filled with liquid methane. The second candidate, Comet Astrobiology Exploration Sample Return (CAESAR), would capture and return to Earth a sample from the nucleus of 67P/Churyumov-Gerasimenko—a comet previously explored by the European Space Agency's Rosetta spacecraft.
Rather than selecting three final candidates, as it has in the past, NASA opted for a head-to-head competition. "I selected these mission concepts based on their outstanding and visionary science," Thomas Zurbuchen, associate administrator of NASA’s science mission directorate in Washington, D.C., said in a teleconference announcing the finalists. "I didn't start with a number in mind."
Dragonfly is led by Elizabeth "Zibi" Turtle, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. CAESAR is led by Steve Squyres, a planetary scientist at Cornell University who has long led the Spirit and Opportunity rovers on Mars. Dragonfly would be managed by APL, whereas CAESAR would be managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Both missions would feature a long wait: Dragonfly would arrive at Titan in 2034, and CAESAR's samples would return to Earth in 2038.
With hydrocarbon seas that may contain amino acids and other interesting molecules, Titan is thought to be a place for testing ideas for how life arose on Earth. With a suite of spectrometers, drills, and cameras, Dragonfly would split its mission between science in the air and on the ground. The rotocraft could travel up to 100 kilometers between sampling sites, and recharge its batteries between flights with a nuclear power source. Although frigid, Titan is otherwise a relatively benign place, and the rotocraft could survive for several years. That could give the team time, Turtle said, to "evaluate how far prebiotic chemistry has progressed in an environment where we know we have the ingredients for life."
CAESAR would also do something unprecedented, Squyres said, by not just sampling a comet, but capturing both dust and volatile ices from its interior. Comets are thought to contain the early building blocks of the solar system, and returning such samples to Earth would allow close analysis. By returning to 67P/Churyumov-Gerasimenko, a body mapped in detail by Rosetta, the mission can target the best sites for retrieving samples, which it will divide into volatile and nonvolatile components for the journey back to Earth. "We're able to design our spacecraft specifically for the conditions we know," Squyres said.
The picks deal another blow to the small pool of researchers who have longed for NASA to return to Venus. One-fourth of the proposed New Frontiers missions targeted Venus, but like other recent competitions, NASA could not convince itself to move a mission toward flight. One of the Venus proposals, led by Goddard’s Lori Glaze, was selected for further technology development, however, along with a mission targeting Enceladus, the saturnian moon with perhaps the best chance of supporting life, led by Chris McKay of NASA’s Ames Research Center in Mountain View, California.
The cost-capped New Frontiers program, with $850 million set out for the mission and about $150 million for the launch, is the largest planetary exploration line that NASA opens to outside competition and leadership. Each candidate must target research priorities from a list set by the scientific community, which this time included a return to Venus; probing of Saturn or its ocean moons; exploration of the moon's south pole; or returning a sample from a comet, among other options.
Previous spacecraft launched under New Frontiers include New Horizons, which surveyed Pluto and is now due to visit MU69, an icy object in the farthest reaches of the solar system; Juno, now in orbit around Jupiter; and OSIRIS-REx, launched last year, which will collect samples from an asteroid and return them to Earth.