Complex situation
"This is a complex situation," said Edward Weiler, NASA associate administrator for the Office of Space Science. The space agency will issue a mid-January "announcement of opportunity" for "the best minds in the country" to come up with alternative plans for a mission to Pluto that could fit within NASA's budget, he said.
Scientists with NASA's Solar System Exploration Subcommittee, an advisory group to the space agency, told Weiler they could accept a small slip in dispatching a mission to Jupiter's moon Europa in 2008, to fit in a Pluto mission within NASA's outer planets program. However, a slip to 2011 is not acceptable for the Europa mission, he said.
"We are trying to get them both launched in this decade. That's the goal," Weiler said.
The opportunity to use Jupiter as a gravity assist to reach Pluto necessitates a spacecraft launch in 2004 or 2006, at the latest. "This is likely the last chance to get to Pluto for a decade or more," Weiler said.
"We are not making a commitment to do a Pluto mission or to select any of the proposals," Weiler stressed. "We just want to see if we have any viable options," he said.
NASA will cap the cost of the Pluto mission at $500 million, in fiscal year 2000 dollars.
"I don't want to get a Pluto mission that is 'unobtainium.' That would automatically push Europa out," Weiler said. "There is no room for mistakes. I don't want over promising and underbidding. I don't want people to promise me things they can't deliver," he told SPACE.com.
Freeze out
By launching a probe to Pluto no later than 2006, scientists could reach the planet before its thin atmosphere collapses in 2020 -- a cycle that occurs every time Pluto's elliptical orbit starts tracking toward its farthest distance from the Sun.
"There is general agreement in the science community that the atmosphere will freeze out. There are honest differences of opinion about how fast and how completely," said Jay Bergstralh, NASA's acting director of solar system exploration.
"As time goes on, over the next decade or two, what remains of the Pluto's atmosphere will be more and more tenuous as the planet recedes from the Sun," Bergstralh said.
The study of Pluto's atmosphere is considered key to understanding the tiny planet.
in an elliptical path. It passed through its perihelion -- the closest point to the Sun during an orbit -- a decade ago. As Pluto moves farther from the Sun it will cool, and its tenuous atmosphere -- with a surface pressure just a few millionths that of Earth -- will begin to freeze. That atmosphere is expected to freeze out completely within the next two decades, depriving scientists of a chance to study it for more than two centuries. Pluto completes its orbit around the Sun every 248 years.
Cast the net widely
The Pluto mission is bundled with the Europa Orbiter mission under NASA's Outer Planets Program.
Weiler also announced that a NASA workshop will be held in early February to stimulate new ideas for outer planet exploration, including possible reshaping of the Europa orbiter mission.
"We want to cast the net widely to formulate a real outer planets program that includes more than two missions over a decade-and-a-half," Weiler said.
Pluto is the only planet in our solar system unvisited by a spacecraft. Some scientists have
to the Pluto mission, saying the Europa mission deserves immediate attention."Europa may harbor the only ocean in the solar system, other than on Earth. If you have water, energy, and hydrocarbons, you have life," Weiler said. "Europa is a very, very important mission."
Weiler said that due to intense radiation at Europa, sending a spacecraft to that Jovian moon is challenging. The Pluto mission is simpler to do than sending a probe to Europa, he said.
"Europa is not a place you want to send grandma. It's a tough place to go to," Weiler said.
Weiler encouraged mission planners to consider using novel propulsion methods for arriving quickly at Pluto, such as ion propulsion.
While the announcement of opportunity regarding the Pluto-Kuiper Express mission will be issued in mid January 2001, proposals will be due in March.
If ideas received are worthy of consideration, NASA will then award funds to the winning ideas to flesh them out further. A final decision on the Pluto mission would be announced in fall 2001.
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