On July 25, 2015, the near-Earth asteroid 1999 JD6 made its closest pass of Earth in at least over a century, coming within 4.5 million miles of our planet (7.2 million kilometers, or about 19 times the distance between Earth and the moon) and traveling at a relative velocity of 45,410 mph (20.3 km/s).
As the 1.2-mile (2 km) asteroid zipped by, NASA aimed two of its largest radio telescopes at it, bouncing radar waves off its surface to measure its size, shape, and rotation.
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The observations revealed that 1999 JD6 is what's known as a "contact binary," a peanut-shaped world that's likely the result of two smaller objects stuck together through their mutual gravitational attraction.
"Radar imaging has shown that about 15 percent of near-Earth asteroids larger than 600 feet [about 180 meters], including 1999 JD6, have this sort of lobed, peanut shape," said Lance Benner of NASA's Jet Propulsion Laboratory in Pasadena, Calif., a specialist in NEOs.