CNN News:NASA计划四个太空探索新项目

NASA, the National Aeronautics and Space Administration, has four ideas it's looking at as possible future missions.
Two of them would focus on Venus. One of them would explore Jupiter's moon Io and one of them would fly by Neptune's moon Triton. I keep saying would because these are just ideas at this point. They'll each be researched by a team over a period of nine months and when the final proposals are made NASA will then decide whether to turn them into actual missions.
So what would scientists hope to learn from all this? As far as Venus goes, one thing they're interested in is its atmosphere which is toxic another is the planet's surface which is hot enough to melt lead. Venus' scorching rocky landscape could be mapped.
Jupiter's moon Io is believed to be the most volcanically active place in our solar system so NASA would like to find out more about the eruptions that happen there. And Triton, a moon that orbits Neptune could also be mapped and studied to see if there are signs of an ocean beneath the moon's surface.

None of these missions would involve astronauts. Robotic spacecraft would be doing the traveling and of course all of them would come at a cost. In fact, the teams that are assigned these subjects will each receive $3 million just to come up with their proposals.
If any of those are approved for missions, space.com says each one would be limited to a price of $500 million but that doesn't include the costs of launching the spacecraft and supporting it while it's in space. And for reference, the Juno mission alone from developing the spacecraft to getting it off the ground to processing all of its information was more than $1 billion. NASA could choose to give two of these new missions the green light.