Image copyright NASA Image caption This illustration shows what NASA’s Voyager 1 spacecraft discovered on Saturn’s rings
NASA scientists want to get rid of proposals for new spacecraft, saying that they are no longer needed because alien life is already here.
A concept team working with the space agency says the planet-hunting Ames Research Centre is used enough for now.
Hans Koenigsmann, who heads the current effort, said the need to pursue that was now “minimal”.
But he wants to see new proposals, in the form of proposals for improved search techniques, in future.
He warned that there could be a limit to how much resources the Ames Research Centre could allocate to the search.
Mr Koenigsmann spoke to the BBC’s Kevin Connolly at the Australasian Planetary Science Congress in Tasmania, Australia.
“We’re looking at Kepler, which is largely completed,” he explained.
“We’re looking at all the aliens out there to make sure, particularly to look out for the missing methane… We’re still continuing, but with fewer people.
“We’re looking for different kinds of planets now – in a sense, I’m no longer sure we really need a new exoplanet-hunting system that’s equivalent to our current Kepler system because we already have a really large exoplanet-hunting system.”
A planet hunt
The astronomical survey NASA uses for its planet-hunting programme, called Kepler, monitors some 150,000 stars.
The size of that survey has increased recently as part of a worldwide upgrade to global earth-observing technologies.
It also carries powerful instruments to search for planets that could be rocky and suitable for life.
The size of an individual star and their habitable zone — the distance that water, on Earth, can remain liquid — are determined by the thickness of the star’s atmosphere.
Some of the planets can also have moons orbiting nearby, giving another picture of an orbiting world.
When asked why NASA is not looking at potential Earth substitutes, such as comets, Mr Koenigsmann said: “I don’t think we need those as much anymore because the planets have been found with spacecraft that orbit the sun.”
The 10-week survey is being run in conjunction with other astronomy projects.
The bulk of the funding for the Kepler programme comes from the Nasa Office of Science and falls under the umbrella of the astrophysics division.