'Potentially hazardous'? An asteroid the size of the Space Needle will pass near Earth. A massive asteroid is expected to whiz by Earth in a relatively close encounter - 4.5 million miles - on Tuesday, according to NASA. The asteroid, known as 2021 KT1, is about 600 feet, the size of the New York Olympic Tower or the Seattle Space Needle. The asteroid is classified by NASA as a "Potentially hazardous object" because it is larger than 492 feet and within 4.6 million miles of Earth. It will be flying near Earth at a speed of 40,000 mph, according to the laboratory. While the asteroid is not expected to make a direct hit, NASA is keeping a close watch. Ref. USAToday.