Washington, May 6 (IANS): A new mission to Saturn's moons Titan or Enceladus to find signs of life beyond Earth cannot be ruled out as NASA says it is reviewing 12 proposals for future unmanned solar system mission to be launched in the mid-2020s.

The proposed missions of discovery -- submitted under NASA's New Frontiers programme - will undergo scientific and technical review over the next seven months, the US space agency said in a statement on Friday.

Selection of one or more concepts for Phase A study will be announced in November. At the conclusion of Phase A concept studies, it is planned that one New Frontiers investigation will be selected to continue into subsequent mission phases.

Investigations for this announcement of opportunity were limited to six mission themes - comet surface sample return; lunar South Pole-Aitken basin sample return; ocean worlds (Titan and/or Enceladus); Saturn probe; Trojan tour and rendezvous; and Venus in situ explorer

"New Frontiers is about answering the biggest questions in our solar system today, building on previous missions to continue to push the frontiers of exploration," said Thomas Zurbuchen, Associate Administrator for NASA's Science Mission Directorate in Washington.

"We're looking forward to reviewing these exciting investigations and moving forward with our next bold mission of discovery," Zurbuchen said.

The New Frontiers Programme conducts principal investigator (PI)-led space science investigations under a development cost cap of approximately $1 billion.

This would be the fourth mission in the New Frontiers portfolio. Its predecessors are the New Horizons mission to Pluto, the Juno mission to Jupiter, and OSIRIS-REx, which will rendezvous with and return a sample of asteroid Bennu.