High winds forced NASA to scrub the launch Tuesday of an unmanned spacecraft on a nine-year, 3-billion-mile voyage to Pluto, the solar system's last unexplored planet.

NASA planned to try again Wednesday to launch the New Horizons probe, although the forecast held a greater chance of thunderstorms, clouds and gusty winds that could prevent a launch.

On Tuesday, winds at the launch pad exceeded the space agency's 38 mph flight restriction.

"The winds picked up sooner than expected," said MIT scientist Richard Binzel, one of the mission's investigators. "Blame the meteorologists."


"What we know about Pluto today could fit on the back of a postage stamp," Colleen Hartman, a deputy associate administrator at NASA, said earlier. "The textbooks will be rewritten after this mission is completed."




Pluto is the brightest body in a zone of the solar system known as the Kuiper Belt, made up of thousands of icy, rocky objects, including tiny planets whose development was stunted by unknown causes. Scientists believe studying those "planetary embryos" can help them understand how planets were formed.


An Atlas V rocket had been programed to speed New Horizons away from Earth at 36,000 mph, the fastest launch speed on record.

Once launched, the craft was expected to reach Earth's moon in about nine hours and arrive in 13 months at Jupiter, where it will use the giant planet's gravity as a slingshot, shaving five years off the 3-billion-mile trip.

The distance involved means scientists will not be able to receive data on Pluto until at least July 2015, the earliest date the mission is expected to arrive.

Some NASA safety managers had raised concerns about a rocket fuel tank since a similar test tank failed a factory pressure evaluation. The decision was made to attempt the launch since the flight tank was in pristine condition and had no signs of any defects like the ones found on the test tank, said NASA launch director Omar Baez.

Thirty anti-nuclear protesters showed up recently to oppose this mission's plutonium-powered generator, compared with hundreds who protested the launch more than eight years of the Cassini mission to Saturn, which carried 72 pounds of plutonium.

The two Mars rovers, Spirit and Opportunity, sent up in 2003, had much smaller amounts of plutonium, which also was used on six Apollo flights.

NASA and the Department of Energy estimated the probability of a launch accident that could release plutonium at 1 in 350. As a precaution, the agencies brought in 16 mobile field teams that can detect radiation and 33 air samplers and monitors.