NASA halted work on its Pluto-Kuiper Express mission last year, citing the cost of the project. In December, the agency revived hopes for a mission by saying it would accept new proposals from universities or research institutions.

NASA stipulated, however, that the project must cost less than $500 million and deliver a spacecraft to Pluto [reference page] by 2020. Proposals are due by March, but NASA has made it clear that it reserves the right to not select any of the bids.

The Planetary Society intends to push NASA into accepting one of the proposals, Huntress said.

"We know how to do this mission," said Alan Stern of the Boulder, Colorado-based Southwest Research Institute. "Theres one thing we dont know how to do -- get it out of the Washington Beltway."

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Panelists and audience members recommended a letter writing campaign to lawmakers, especially those on the House and Senate Appropriations VA-HUD and Independent Agencies Subcommittees, which control NASAs purse strings.

Panelist noted that the window of opportunity for a Pluto mission is closing. The planet revolves around the Sun in an elliptical orbit. The longer the mission is postponed, the less sunlight will fall on its surface. By 2020, only a quarter of the planets surface will be bright enough to be studied. As it recedes, its unique atmosphere will collapse.

"It doesnt matter if we go there in the Starship Enterprise, there wont be an atmosphere to study," Stern said.

NASA can send missions to Saturn [reference page], Jupiter [reference], Neptune [reference] and Uranus [reference] "at its leisure," Stern added. But this generation will only have one shot to go to Pluto, he said.

Neil de Grasse Tyson, director of the New York-based Hayden Planetarium, said he believes Pluto is not a planet but rather a larger member of the so-called Kuiper Belt [reference page] of ice and rock asteroids. However, he said he strongly supports a mission to Pluto that would also explore some of its smaller Kuiper Belt neighbors.

"Theres enough uncertainty [about Pluto] that we want to know more about this place.... Theres something to be learned out there."

Pluto and its relatively large moon, Charon [reference page], are similar to Earth and its own moon, Stern said. Getting a closer look at Pluto may help scientists understand the origin of the solar system and how Earths moon formed.