A lander heads for Comet 67P/Churyumov-Gerasimenko during the European Space Agency’s Rosetta mission. NASA/ESA

NASA might send a spacecraft to collect samples from a comet or it might visit Titan as part of its search for extraterrestrial life in the universe.

The space agency held a teleconference on Wednesday to announce the finalists in a contest to design its next New Frontiers program mission, which could launch in 2025. It chose Dragonfly, a mission to Titan that would investigate how habitable that moon of Saturn is, and Comet Astrobiology Exploration Sample Return, also known as CAESAR, which would bring home samples from Comet 67P.

Comet 67P is special because a spacecraft has already landed on it — the European Space Agency’s Rosetta mission flew around it in space for a couple of years and sent a lander crashing to its surface.

Titan also saw some action when the Cassini spacecraft, which spent several years orbiting Saturn and its moons and dramatically ended its mission in September by crashing into the ringed gas giant, sent the Huygens space probe down to Titan’s surface so scientists could gather data about the large moon’s atmosphere and surface.

CAESAR was proposed through Cornell University while Dragonfly is designed by the Johns Hopkins University Applied Physics Laboratory.

Between the funding NASA is offering to build one of these missions and the cost of its operation and launch, the space agency is projected to spend about $1 billion on the lucky winner. That winner will be chosen in 2019.

New Frontiers is geared toward furthering solar system exploration and has already launched the Juno spacecraft to examine Jupiter and its moons; the New Horizons spacecraft to Pluto and the cloud of icy rock at the edge of the solar system called the Kuiper Belt; and the OSIRIS-REx spacecraft that is currently headed for the asteroid Bennu with the goal of collecting samples in 2018 and bringing them back to Earth in 2023.

In choosing the missions to Comet 67P and to Titan as finalists, NASA declined other proposals that would have sent spacecraft to Venus, Earth’s moon, Saturn’s moon Enceladus and a couple of other comets.

The CAESAR mission would look to get information about the Comet 67P’s origin, according to NASA, which in turn could teach us more about the history of the solar system. Dragonfly would use "a drone-like rotocraft that would explore the prebiotic chemistry and habitability of dozens of site on Saturn’s moon."