While the agency typically keeps New Frontiers submissions a secret, the themes it listed when it was looking for submissions can give you an idea of what they're about:
- Comet Surface Sample Return
- Lunar South Pole-Aitken Basin Sample Return
- Ocean Worlds (Titan and/or Enceladus)
- Saturn Probe
- Trojan Tour and Rendezvous
- Venus In Situ Explorer
During a talk about Cassini's Grand Finale, Linda Spilker, one of the project's scientists, revealed that three of the proposals want to continue the probe's work. One of them wants to bring back gas from Saturn's atmosphere, while another wants to explore Titan's hydrocarbon lakes. The last one intends to get samples from Enceladus' geysers and to analyze them for amino acids, which are a possible indicator of life.
NASA aims to launch the mission it chooses by 2024, and based on previous New Frontiers projects, we might be in for a lot of fascinating discoveries and high-res images. New Horizons took the closest photos of Pluto we've ever seen, Juno (pictured above) is exploring Jupiter and has been capturing detailed images, as well, while Osiris-Rex is on its way to rendezvous with near-Earth asteroid Bennu.