NASA said scientists with the agency's Deep Space Network at Goldstone, Calif., and the Arecibo Plantetary Radar Facility in Puerto Rico will be tracking asteroid 2005 YU55, which will make its closest approach to earth Tuesday at 3:28 p.m. PST, when it will be 0.85 the distance from the moon to earth.
"The last time a space rock as big as 2005 YU55 came as close to Earth was in 1976, although astronomers did not know about the flyby at the time," NASA said on its Web site.
The next known approach of an asteroid this large will be in 2028.
NASA scientists will use antennas to track the asteroid from the Deep Space Network and bounce radio waves off the space rock from Arecibo Observatory. Radar echoes returned from the asteroid will then be collected and analyzed.