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Scientists clamor for Pluto, Europa missions

Pluto and its moon Charon, as seen through the lens of the Hubble Space Telescope  

By Richard Stenger

(CNN) -- Space exploration enthusiasts are urging Congress to restore funding to proposed missions to the solar system's most distant planet and a jovian moon thought to possess a saltwater ocean.

The Pluto and Europa projects, which the White House targeted for cancellation earlier this year for budgetary reasons, were among the top mission priorities endorsed this week by the National Research Council. The council polled professional scientists and space enthusiasts at the behest of NASA to assess priorities for unmanned scientific missions over the coming decade.

"While the report encompasses all aspects of planetary exploration, the pressing issue before Congress is whether it will now overturn the administration's proposed cancellation of the Pluto/Kuiper Belt flyby and Europa orbiter missions," said Louis Friedman, director of the Planetary Society.

"A mission to the Kuiper Belt, including Pluto-Charon, will provide the first exploration of this newly discovered domain in our system," Friedman said in a statement. "Europa holds the most promise for understanding the biological potential of icy satellites."

Many astronomers classify Pluto and its moon Charon as minor planets known as Kuiper Belt objects, a group of perhaps thousands of icy bodies that ring the outer reaches of the solar system.

Europa, one of the largest moons of Jupiter, is considered one of the most promising spots in the search of extraterrestrial life. Scientists theorize that it contains vast reservoirs of liquid water that could sustain primitive life.

The first mission, originally slated to launch in 2006, would fly by Pluto, Charon and more remote Kuiper Belt objects. The second mission, tentatively scheduled to launch in the decade, would orbit Europa and study its icy surface and subsurface ocean.

Time is of the essence for a Pluto expedition. The planet travels in a highly eccentric orbit and now is heading further from the sun. Should a mission be delayed several years, it might arrive after the planet's tenuous atmosphere has frozen over completely -- a seasonal big chill that can last more than 100 years, according to astronomers.

"The Pluto/Kupier Belt mission is the best opportunity for exploration of these objects for decades, if not centuries," Friedman said.

The icy moon of Europa, imaged by the Galileo probe
The icy moon of Europa, imaged by the Galileo probe  

The NRC, part of the National Academy of Sciences, outlined priorities for robotic space missions. Besides Pluto and Europa, the council endorsed missions to the moon, Venus, Jupiter, Io -- another large jovian moon -- and a comet.

Most of the projects would be considered small or medium-sized ones, meaning their price tags would run from about $300 million to $600 million, the report said.

But less frequent flagship missions, to be undertaken once every decade or so, would likely cost in excess of $1 billion, it added. Once such mega-mission is the Europa one.

"You can't do the Europa mission cheaply because of the harsh environment in which that mission will operate. Yet these [flagship missions] are critical to approaching some of the very important questions we wish to address," said astronomer Michael Belton, who chaired the NRC committee.




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