Astronomers searching the skies for orbiting space rocks have made a startling discovery: a giant “planet killer” asteroid is speeding through space on a collision course with Earth’s orbit. The asteroid, called 2022 AP7, is believed to be 7,546 feet across — placing it among the top 5 percent of the largest asteroids ever discovered, says Scott Sheppard of the Carnegie Institution for Science. “Any asteroid over 1 kilometer in size is considered a planet killer,” Sheppard says. Should 2022 AP7 collide with the planet, it would cause “a mass extinction event like hasn’t been seen on Earth in millions of years,” he says. Fortunately, that’s not going to happen, Sheppard says. While 2022 AP7 will cross Earth’s orbit, the planet will be on the other side of the sun when it happens, he explains. What’s the most amazing thing you’ve seen in the sky?