Asteroid 2021 RS2 geocentric flyby diagram via Minor Planet Center/ The Watchers.
Small asteroid skimmed close to Earth
Astronomers at Mount Lemmon in Arizona discovered a car-sized asteroid yesterday (September 7, 2021). Quick calculations of its trajectory showed it was due to skim past our planet just hours after its discovery. According to NASA’s Center for Near Earth Object Studies (CNEOS), the asteroid’s closest approach came at 07:28 UTC (3:28 a.m. EDT) on September 8. The asteroid now carries the designation 2021 RS2. It’s the closest space rock to pass by Earth so far in 2021. According to The Watchers website, it’s the 81st known asteroid to fly by Earth inside one lunar distance since the start of 2021.
Asteroid 2021 RS2 came just 9,532 miles (15,340 km) from Earth’s surface. Was that close? Yes, really close. Earth’s diameter is about 7,917.5 miles (12,742 km). So we can say the new-found space rock was passing slightly farther than one Earth-diameter.
The small asteroid was traveling at 39,366 miles per hour (63.353 km/h) or 17.59 kilometers per second, relative to Earth.
But … this object is small. Its size is estimated at just 11.5 feet (3.5 meters) in diameter. ...