NASA's Deep Impact probe is scheduled to lob a big copper "bullet" into a comet on July 4 to look into the heart of this remnant from the formation of our solar system, scientists said on Thursday. Impact is expected at 1:52 a.m. EDT (0552 GMT) on U.S. Independence Day. About a day before the collision, the Deep Impact craft will send a 317-pound (144 kg) copper-fortified impactor toward comet Tempel 1, which will be about 83 million miles (133.6 million km) from Earth. The impactor will steer itself toward the comet and the Deep Impact craft will pass about 310 miles (500 km) away from it and watch the smash-up, the scientists said at a briefing. Rick Grammier, the project manager for the mission, called this maneuver "extremely challenging". "It's a bullet trying to hit a second bullet with a third bullet, in the right place at the right time, watching the first two bullets and gathering the scientific data from that impact," Grammier said. --More 2242 Local Time 1942 GMT
