This NASA illustration shows Florence, an asteroid that passed within 4.4 million miles (7.0 million kilometers) of Earth last week. Radar images revealed that Florence has two moons

Florence, an asteroid that came within 4.4 million miles (7.0 million kilometers) of Earth last week, has two small moons, according to radar images obtained by NASA.

Radar images obtained between August 29 and September 1, when Florence came closest to Earth, reveal that the asteroid is about 2.8 miles (4.5 kilometers) in size, the US space agency said.

It said the two moons were probably between 300-1,000 feet (100-300 meters) across.

The inner moon takes approximately eight hours to revolve around Florence while the outer moon takes between 22 and 27 hours, NASA said.

According to NASA, 60 near-Earth asteroids are known to have moons and Florence is the first observed with two moons since Asteroid 1994 in June 2009.

NASA said the radar images of Florence, which was discovered in 1981, were obtained by the Goldstone Deep Space Communications Complex in California.

"While many known asteroids have passed by closer to Earth than Florence... all of those were estimated to be smaller," said Paul Chodas, manager of NASA's Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory in Pasadena, California. "Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began."

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