There was no reason to fret, but perhaps reason to be wowed: "Florence," an asteroid stretching an estimated 2.7 miles wide, became the largest known asteroid to come as close as it did to our planet when it whizzed by Friday at 8:06am EDT. But though it came relatively close to Earth by space standards, it was still 4.4 million miles away, or about 18 Earth-Moon distances, according to NASA. Astronomers who've mapped Florence's orbit were well aware the asteroid posed no danger to Earth—and it won't get any closer to us until after 2500—and were thrilled at the prospect of its flyby, which provided an opportunity to study the mass up close. Radar images could perhaps reveal details of Florence's surface as small as 10 feet wide, per Space.com.
The images may also allow astronomers to gauge Florence's true size and shape for the first time. Until now, they've only been able to speculate that it may take "the shape of a top" with "a bulge at the equator," Paul Chodas of NASA's Jet Propulsion Laboratory tells Space.com. That's a common form for fast-spinning asteroids like Florence—named after Florence Nightingale and one of an estimated 10 large asteroids flying in near-Earth space. "If it were spinning any faster, it would fly apart," says Chodas, who says of the flyby, "Nothing this big has passed this close to Earth since we've been tracking." (The asteroid that wiped out the dinosaurs was twice as big.)