NASA's New Frontiers program consists of a series of unmanned missions with the intent of exploring the solar system. The missions are designed to target specific goals as defined by the broader planetary community. Yesterday, NASA announced the two finalists for a robotic New Frontiers mission, with a planned launch in the mid-2020s. One is a sample return mission to a comet; the other is to explore Saturn's moon Titan. The first mission, called CAESAR, or Comet Astrobiology Exploration Sample Return intends to send a spacecraft back to 67P/Churyumov-Gerasimenko. This is the same comet that the ESA spacecraft Rosetta explored.

The field for NASA's next New Frontiers mission is narrowing. Officials announced the two finalists for a new robotic explorer mission -- one that would send a spacecraft to bring samples of the comet 67P/Churyumov-Gerasimenko to Earth, and another to explore Saturn's moon Titan. The two mission concepts, CAESAR and Dragonfly, detailed in a NASA briefing Wednesday, beat out 10 other proposals to explore solar system targets including a basin on the moon; the surface of Venus; and Enceladus, the icy ocean world that also circles Saturn. "The New Frontiers program is really the premier program for our principal investigators and indeed it's one of the most difficult programs to be selected for," said Jim Green, director of the Planetary Science Division at NASA Headquarters in Washington. NASA only selects about two of these medium-class missions every decade, he added.