Closeup Comet

By ALICIA CHANG, AP Science Writer – Thu Nov 4, 9:00 pm ET

PASADENA, Calif. – A NASA spacecraft sped past a small comet Thursday, beaming pictures back to Earth that gave scientists a rare close-up view of its center. Mission controllers burst into applause upon seeing images from the flyby that revealed a peanut-shaped comet belching jets of poisonous gases.

"It's hyperactive, small and feisty," said mission scientist Don Yeomans of the NASA Jet Propulsion Laboratory.

The close encounter occurred 13 million miles from Earth when the Deep Impact craft, hurtling through space, flew within 435 miles of comet Hartley 2. It's only the fifth time that a comet's core has been viewed up close.

Scientists are interested in comets because they're icy leftovers from the formation of the solar system about 4.5 billion years ago. Studying them could provide clues to how Earth and the planets formed and evolved.

"The scientific work is just beginning now," principal investigator Michael A'Hearn, of the University of Maryland, said at a post-mission news conference. "The engineers did a fantastic job of getting us data. Now we have to make sense of it."

Thursday's flyby is actually an encore mission for Deep Impact. It set off cosmic fireworks on July 4, 2005, when it fired a copper probe that crashed into comet Tempel 1. The high-speed collision spewed a cloud of debris into space, giving scientists their first peek of the interior.

After the $333 million comet-buster, NASA recycled Deep Impact for a new mission to visit another comet. It was supposed to target comet Boethin in 2008, but it was nowhere to be found. Scientists theorized the comet may have broken up into small pieces.

Deep Impact was then redirected to Hartley 2. Roughly 1 1/2 miles long, Hartley 2 is the smallest comet to be photographed up close. On its way there, the craft spent several months scanning a cluster of nearby stars with known planets circling them.

While its latest task lacks the Hollywood drama of the Tempel 1 crash, researchers still consider it an important mission. Unlike in 2005, viewers could not see Thursday's comet encounter in real time since the craft's antenna was not pointed at Earth as it flew past Hartley 2.

"There are a lot of open questions about comets and their life cycle," said project manager Tim Larson of JPL, which manages the $42 million encore mission. "We have so little data that every time we have an opportunity to go near a comet, it's a chance to expand our knowledge."

Since September, Deep Impact has been stalking Hartley 2 like a paparazzo, taking images every 5 minutes and gathering data. It's the first craft to visit two comets.

Deep Impact will observe Hartley 2 until Thanksgiving and then wait for further instructions from NASA. Thespace agency has not decided whether to reuse Deep Impact again. The craft does not have enough fuel on board to do another flyby.

The latest images add to scientists' cometary photo album, said astronomer David Jewitt of the University of California, Los Angeles, who had no role in the project.

"We're visual animals and nothing seems wholly real to us until we have a nice picture of it," Jewitt said.

Hartley 2 passed within 11 million miles of Earth on Oct. 20 — the closest it has been to our planet since its discovery in 1986.

British-born astronomer Malcolm Hartley, who discovered the comet, said he never imagined a spacecraft would get so close to his namesake find.

"When I saw the comet, it was millions and millions of kilometers away," he said. "I'm extremely excited and feel very privileged. After all, I only discovered it."

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Online:

Comet mission: http://epoxi.umd.edu/

2 big satellites collide 500 miles over Siberia

AP Associated Press:

NASA said it will take weeks to determine the full magnitude of the crash, which occurred nearly 500 miles over Siberia on Tuesday.

"We knew this was going to happen eventually," said Mark Matney, an orbital debris scientist at Johnson Space Center in Houston.

NASA believes any risk to the space station and its three astronauts is low. It orbits about 270 miles below the collision course. There also should be no danger to the space shuttle set to launch with seven astronauts on Feb. 22, officials said, but that will be re-evaluated in the coming days.

The collision involved an Iridium commercial satellite, which was launched in 1997, and a Russian satellite launched in 1993 and believed to be nonfunctioning. The Russian satellite was out of control, Matney said.

The Iridium craft weighed 1,235 pounds, and the Russian craft nearly a ton.

No one has any idea yet how many pieces were generated or how big they might be.

"Right now, they're definitely counting dozens," Matney said. "I would suspect that they'll be counting hundreds when the counting is done."

As for pieces the size of micrometers, the count will likely be in the thousands, he added.

There have been four other cases in which space objects have collided accidentally in orbit, NASA said. But those were considered minor and involved parts of spent rockets or small satellites.

Nicholas Johnson, an orbital debris expert at the Houston space center, said the risk of damage from Tuesday's collision is greater for the Hubble Space Telescope and Earth-observing satellites, which are in higher orbit and nearer the debris field.

At the beginning of this year there were roughly 17,000 pieces of manmade debris orbiting Earth, Johnson said. The items, at least 4 inches in size, are being tracked by the U.S. Space Surveillance Network, which is operated by the military. The network detected the two debris clouds created Tuesday.

Litter in orbit has increased in recent years, in part because of the deliberate breakups of old satellites. It's gotten so bad that orbital debris is now the biggest threat to a space shuttle in flight, surpassing the dangers of liftoff and return to Earth. NASA is in regular touch with the Space Surveillance Network, to keep the space station a safe distance from any encroaching objects, and shuttles, too, when they're flying.

"The collisions are going to be becoming more and more important in the coming decades," Matney said.