After having successfully reconnoitered its first asteroid last year, NASA's Near Earth Asteroid Rendezvous spacecraft, or NEAR, will flash into view late Thursday night and early Friday morning across much of the United States. NEAR will swing within 540 kilometers of Earth's surface on its way to a close encounter with another asteroid, Eros. NEAR's solar panels will reflect the sun's light during its swift passage, treating observers to an ephemeral "sunglint" as bright as the night's most brilliant stars Last June, the $210 million spacecraft flew within 1200 kilometers of the asteroid Mathilde, dazzling planetary scientists with images of a primitive and severely battered object (Science, 4 July 1997, p. 30 ). NEAR's views of Eros, which it will orbit starting in January 1999, are expected to be 50 times sharper. A full year of data promises to reveal much about Eros's origins and composition: Some researchers speculate that it may be a floating "rubble pile." NEAR's mission to Eros, which orbits the sun between Earth and Mars, will end with an attempt to land on the asteroid's surface.
Tomorrow's slingshot around Earth will send NEAR on the proper trajectory to Eros while accelerating the craft to more than 46,000 kilometers per hour. During the swing-by, project scientists will calibrate NEAR's timing clock and check its navigation via a series of slight changes in the spinning flywheels that control NEAR's orientation. The craft will direct a beacon of reflected sunlight on a wavy path across the United States, between 1:25 a.m. and 1:48 a.m. EST on Friday, appearing as a slowly moving new "star" in the constellation Perseus. The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, which manages the mission, has posted detailed star charts and viewing times on its Web site .
David Dunham, NEAR's mission design chief, will coordinate a national network of amateur astronomers to observe the apparition. "If the solar panels aren't perfectly aligned, the 'star' will brighten in steps," Dunham explains. "Precise timings of the brightness pattern will help us align the panels." NEAR also will produce a movie of Earth during its flyby, with an especially stunning view of Antarctica as the spacecraft recedes from Earth.