An asteroid nearly two miles (three kilometers) wide is set to pass by Earth Friday with no risk of impact, offering scientists a rare chance to study a massive flying object with its own moon.
Asteroid 1998 QE2 will make its closest approach to Earth at 4:59 pm (20:59 GMT), at a distance of 3.6 million miles (5.8 million kilometers), or about 15 times the distance between Earth and the moon, the US space agency said.
"This is the closest approach the asteroid will make to Earth for at least the next two centuries," NASA said.
The asteroid will not be visible to the naked eye, but radar astronomers are already studying it with complementary imaging telescopes in California and Puerto Rico and will continue to analyze it until June 9.
On Thursday, NASA scientists using the 230-foot (70-meter) Deep Space Network antenna at Goldstone, California reported that the asteroid, first discovered in 1998, also appears to have its own moon.
The huge flying object is known as a binary asteroid, and is circled by a satellite, or moon, that is about 2,000 feet (600 meters) wide, NASA said.
Scientists hope that measurements gathered as the asteroid approaches will help space agencies track other asteroids, including those that might impact the Earth, and calculate their orbits further in advance.
"Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than if radar observations weren't available," NASA said.
The asteroid-moon duo is in rare company—NASA says about 16 percent of asteroids that are 655 feet (200 meters) or larger are binary or triple systems.
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