Fearing that an opportunity to study Pluto's tenuous atmosphere might be lost for centuries, scientists this week expressed their concern over NASA's plans to delay a spacecraft mission to the distant planet Fearing that an opportunity to study Pluto's tenuous atmosphere might be lost for centuries, scientists are expressing their concern over NASA's plans to delay a spacecraft mission to the distant planet.
The Division for Planetary Sciences (DPS) of the American Astronomical Society issued a statement last Thursday expressing its concern over a directive issued by NASA earlier this month that stopped work on the
Pluto-Kuiper Express (PKE) mission.NASA associate administrator Ed Weiler told Congress last week that he issued the stop-work order because the cost of PKE and a related mission, Europa Orbiter, has doubled from a 1998 estimate of $700 million, largely because of launch vehicle costs and technologies needed for the two missions.
An artist's rendering of the proposed Pluto-Kuiper Express mission, which may face cancellation.
Weiler said he stopped work on PKE so that NASA could focus on Europa Orbiter, a mission he said was a higher priority that the Pluto probe. "Basically, I directed the project to go full speed
on Europa to give us the earliest possible launch of that mission," Weiler told a House of Representatives subcommittee September 13.That decision did not sit well with the DPS, whose 1,225 members make up the world's largest professional organization devoted to planetary science. The DPS said that astronomers have expressed "major concerns" over the decision to halt work on PKE.
The DPS "has urged that NASA and the U.S. Congress to find a way to fund this important mission, but not at the expense of other equally important planetary missions or its basic research and analysis programs," it noted in a statement.
The concerns about the mission focus largely on its time-sensitive nature. PKE was to launch in 2004 and use a gravity-assist flyby of Jupiter to arrive at Pluto around 2012. If the launch is delayed much beyond 2004, the window for the Jupiter gravity-assist will close, delaying the spacecraft's arrival at Pluto by as much as seven years.
Moreover,
Pluto goes around the sun in an elliptical orbit, and passed through perihelion -- the closest point in its orbit to the sun -- a decade ago. As Pluto moves away 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 out. 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.~
Weiler said he was aware of the unique constraints for a Pluto mission when he made the decision to stop work on PKE. "Certainly after 2006, I believe, we miss the deadline [for a Jupiter flyby] and miss the opportunity for many, many years down the road," he said. "But all that taken into consideration, I still believe that Europa is a higher priority mission."
The DPS leadership believes that work on PKE must resume by the end of the year to avoid missing a 2004 launch date. To that end, the organization is talking with NASA and Congress about the mission, according to DPS chairman Robert Nelson, an astronomer at JPL.
"The DPS has an ongoing dialogue with NASA, its advisory committees and with Congress, and there is nothing to prevent this issue from being discussed," he said. Further action, he noted, "is still under discussion."
"Certainly after 2006, I believe, we miss the deadline [for a Jupiter flyby] and miss the opportunity for many, many years down the road. But all that taken into consideration, I still believe that Europa is a higher priority mission."
Nelson also said that the DPS was open to working with other organizations, such as The Planetary Society, about PKE. The society called on its 100,000 members last week to write members of Congress, urging them to restore funding for the mission.
"A modest increase in the NASA budget -- say 2 percent -- would solve the funding problem for the Outer Planets program," said
Lou Friedman, executive director of The Planetary Society.Alan Stern, director of the Department of Space Studies at the Boulder, Colorado office of the Southwest Research Institute and a longtime proponent of a Pluto mission, said that while he was "very surprised" at the stop-work order, he was optimistic that funding for the mission would resume soon.
"The exploration of Pluto-Charon and the Kuiper Belt is both scientifically and publicly appealing, and popular," he said. As for getting a mission to Pluto before its atmosphere freezes out, he concluded, "if we can launch by 2004 or perhaps 2006, we're in good shape. Otherwise, my feeling is that all bets are off."
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