NASA selected two finalists for the next New Frontiers planetary science mission today (December 20, 2017). CAESAR, a comet sample return mission, would go back to the same comet visited by the European Space Agency’s (ESA’s) Rosetta spacecraft. The other, Dragonfly, would send a drone-like vehicle to explore the surface of Saturn’s moon Titan, which was briefly studied in 2005 by ESA’s Huygens probe as part of the NASA-ESA Cassini-Huygens mission. The new missions would build on what was learned earlier. NASA also will fund enhanced technology development for two other potential missions, one to land on Venus and the other to study Saturn’s moon Enceladus.

New Frontiers is series of Principal Investigator (PI)-led missions that cost approximately $1 billion ($850 million without launch), a mid-sized planetary exploration mission (larger than the Discovery-class, but smaller than a flagship). Three New Frontiers missions have been launched to date: the New Horizons mission that flew past Pluto in 2015 and is now enroute to fly past a Kuiper Belt object; the Juno mission currently orbiting Jupiter; and the OSIRIS-REx asteroid sample return mission now enroute to Bennu.

In April, NASA received 12 proposals for the New Frontiers 4 (NF-4) selection. Thomas Zurbuchen, head of NASA’s Science Mission Directorate, and Jim Green, Director of the Planetary Sciences Division, announced two winners today. Each will be funded by NASA through 2018 to further define the concepts (Phase A), with reports due back to NASA in January 2019. In July 2019, NASA will pick one of the two to move forward.

Comet Astrobiology Exploration Sample Return (CAESAR). Steve Squyres of Cornell University is the PI. He is well known in the planetary science community as the PI of the Spirit and Opportunity Mars rovers that landed on Mars in 2004. Opportunity is still operating today.

If selected, in 2025 CAESAR would be launched to comet 67P/Churyumov-Gerasimenko (or 67P for short), land, collect a sample, and return the sample to Earth in 2038. The project would be managed by NASA’s Goddard Space Flight Center, Orbital ATK would build the spacecraft, and the Japan Aerospace Exploration Agency (JAXA) would provide the sample return capsule. The spacecraft would be solar powered.

ESA’s Rosetta mission studied 67P, captivating the scientific community and the public especially when the Philae lander unexpectedly bounced three times before settling down in an unknown location on the comet in 2014. Philae returned a lot of data about the comet’s surface while its batteries functioned, but its solar panels were not oriented properly to receive enough sunlight to recharge them and contact was lost. Rosetta remained in orbit around 67P as the comet made its way in towards the Sun. Eventually imagery from Rosetta’s cameras located Philae. In September 2016, as the spacecraft reached a point where communications with Earth would be obstructed by the Sun, ESA commanded Rosetta to also land, so the two are now together on the surface as the comet continues its journey back towards the outer edge of the solar system.

Squyres explained at a media teleconference today that he chose 67P as the target for CAESAR exactly because of the extensive data obtained during the Rosetta mission. Every comet has its own history, he said, and by going to 67P “we can design specifically for the conditions we know exist there.”

He is also taking advantage of technology developed by JAXA for its Hayabusa mission that successfully returned a sample of an asteroid in 2010. Squyres explained that the Hayabusa capsule is perfect for CAESAR because it protects the samples from heating during the capsule’s reentry through Earth’s atmosphere. The 67P samples will contain both volatiles and non-volatiles. Heat could ruin the volatile samples because temperatures reach 3,000 degrees during descent, Squyres said. The Hayabusa capsule retains its heat shield until it has passed through most of the heating, protecting the samples.

Dragonfly. Dragonfly is a drone-like rotorcraft that could fly from place to place on Titan, one of Saturn’s moons. The PI is Elizabeth “Zibi” Turtle from Johns Hopkins University Applied Physics Lab (JHU/APL). The project would be managed by JHU/APL, which would also build the radioisotope-powered spacecraft.

If selected, it would be launched in 2025 and arrive at Titan in 2034. ESA’s Huygens probe, delivered to Saturn’s vicinity by NASA’s Cassini spacecraft, descended through Titan’s hazy atmosphere in 2005 and landed, providing the first ever glimpses of the surface. It sent back data via Cassini during its 2 hour 27 minute descent and for another 72 minutes after landing until Cassini set below the horizon. Imagery showed a surface with features that suggest rivers and lakes that scientists theorize could be filled periodically with liquid methane and ethane.

Like Squyres, Turtle pointed to the existing knowledge about the target as an impetus for the mission. Huygens data will make it easier to selecting the best landing sites to maximize scientific return, she said at the teleconference today.

Titan is categorized by NASA as an “ocean world.” Rep. John Culberson (R-Texas), chairman of the House Appropriations subcommittee that funds NASA, is fascinated by the possibility of discovering life in our solar system, which, to the best of our knowledge today, requires liquid water. He directed NASA to create an Ocean Worlds program to focus on studies of such bodies. According to NASA’s Ocean Worlds website, Titan is on the list because it “is believed to have a salty subsurface ocean … beginning about 30 miles below its ice shell. It is also possible that Titan’s ocean is thin and sandwiched between layers of ice, or is thick and extends all the way down to the moon’s rocky interior.” A JHU/APL Dragonfly website states that Titan’s surface is “dominated by water ice” and also has “an interior ocean.” Dragonfly will essentially hop from place to place “to explore potential habitable sites.”

Advanced Technology Development — ELSAH and VICI

NASA will also fund advanced technology development for two mission concepts to help them compete in future selections and more broadly advance the state-of-the-art.

Enceladus Life Signatures and Habitability (ELSAH). Chris McKay of NASA’s Ames Research Center is the PI. Enceladus is another moon of Saturn that is quite different from Titan. It is thought to have a liquid ocean under an icy crust, similar to Jupiter’s moon Europa. NASA’s Cassini spacecraft, which just ended a 20-year mission orbiting Saturn and its moons, detected geysers rising up from the surface of Enceladus. Scientists are eager to sample the material to determine if life might exist in that ocean. The advanced technology development is to develop cost-effective techniques to limit spacecraft contamination and thereby enable life detection measurements on cost-capped missions like those in the New Frontiers category. (Separately, at the direction of Congress, NASA is building a spacecraft to investigate Europa, but that is a flagship mission with greater financial resources at its disposal.)

Venus In-Situ Composition Investigations (VICI). Lori Glaze at Goddard Space Flight Center is the PI. The concept is to land on the surface of Venus, an extraordinarily harsh environment with temperatures over 900 degrees F and a surface pressure 90 times that at the surface of Earth — enough to melt lead. Several Soviet Venera spacecraft landed there, but survived for very short times. The technology development NASA will fund is focused on the Venus Element and Mineralogy Camera so it can operate in that environment.

Note: the title of this article was updated on December 21. The original title was “NASA Wants a Second Look at Rosetta’s Comet and Titan”.