* Last radio communication was on Aug. 8
* Deep Impact spacecraft was launched in 2005
* Studied comets, looked for extrasolar planets
By Irene Klotz
CAPE CANAVERAL, Fla., Sept 11 (Reuters) - NASA has lost radio contact with a pioneering comet probe that hunted for planets beyond the solar system, officials said on Wednesday.
The last radio communications with the Deep Impact spacecraft were on Aug. 8, and recent attempts to contact the probe have failed, NASA said.
Engineers suspect a software glitch is causing Deep Impact's computers to continually re-boot, crippling its ability to fire its steering thrusters and position itself for communications with Earth. The spacecraft's solar panel may also not be pointing toward the sun to generate power.
"The team is now trying to determine how best to try to recover communication," lead scientist Michael A'Hearn, at the University of Maryland, wrote in a mission status report.
The next attempt to contact the spacecraft is expected this weekend, said NASA spokesman D.C. Agle, at the Jet Propulsion Laboratory in Pasadena, California.
Deep Impact was launched in January 2005 for a close-up study of a Comet Tempel 1.
As the probe's name implies, the primary mission, which took place in July 2005, involved the release of an 820-pound (379 kg) metal slug that tore into the comet's nucleus, raising a plume of materials for the mother spacecraft - as well several ground and space-based telescopes - to analyze.
Five years later, Deep Impact sailed by a second comet, Hartley 2, and has made long-distance observations of two other comets, including the recently discovered Comet ISON, which is heading toward a close encounter with the sun in November.
In its extended mission, Deep Impact was used to search for extrasolar planets. With no more fuel for comet visits, the probe has been heading toward the only target it could reach, an asteroid approaching Earth called 2002 GT.
Since the asteroid's orbit brings it as close as 4.7 million miles (7.5 million km) to Earth, astronomers consider it a hazardous object and gained approval from NASA to keep Deep Impact operating in hopes of a 2020 rendezvous.
More recently, Deep Impact was playing a role in an ongoing campaign to study Comet ISON, which scientists believe is making its first pass through the inner solar system.
Deep Impact began making observations in January that showed the comet brightening in a matter of hours. ISON is expected to be within Deep Impact's view through September and again in March through May 2014 after the comet swings around the sun.
The spacecraft returned its first images of ISON in January.
"We have not received any of our expected observations of comet ISON due to a spacecraft problem," A'Hearn wrote.
Comet ISON, which was discovered in September 2012 by two Russian astronomers, may not survive its close encounter with the sun. It has not brightened as much as scientists expected, dampening predictions that it might be visible from Earth even in daylight. (Editing by Jane Sutton and Christopher Wilson)