The first October 31st full moon in decades won't be the only celestial event making this Halloween a little scarier. Scientists say a giant asteroid is expected to come precariously close to Earth the same night. The asteroid, known as 2020 UX3, is about the size of a Boeing 747, according to NASA's Center for Near Earth Studies. It's expected to zip by Earth at a breakneck speed of 36,000 miles per hour, scientists say. Although the massive space rock will be about 3.2 million miles away when it passes Earth, the distance is just a stone's throw in astronomical terms -- and close enough for it to be classified as a "near-Earth object," per NASA.