So even if there's not a lot of advance warning, EarthSky.org said, Earth's atmosphere does a pretty good job of protecting the planet from incoming asteroids, with most exploding high in the atmosphere, or over an ocean, doing little to no harm.
The Catalina Sky Survey and Steward Observatory in Arizona first observed Asteroid 2018 GE3 in the early morning hours on Saturday. "It was shining like a 13th-magnitude star at the time of my observations", Jäger said.
The intensity of the light reflected off of 2018 GE3 indicates that it's between 157 feet and 360 feet wide. This puts it into the exact same class as the 60-meter Tunguska impactor that leveled a forest in Siberia in 1908.
But an asteroid need not be in the Tunguska range to do damage: in 2013, the 65-foot-wide Chelyabinsk meteor exploded over Russian Federation, injuring 1,200 people and smashing thousands of windows. Congress tasked NASA with tracking all objects bigger than 460 feet wide, which 2018 GE3 falls shy of, but NASA has only been able to identify about one-third of the estimated total so far.
If 2018 GE3 had hit Earth, it would have caused regional, not global, damage, and might have disintegrated in the atmosphere before reaching the ground.
It's common for asteroids to be spotted for the very first time at this relatively close distance, but this particular space rock is among the largest ever to come that close to the surface of our planet. 2018 GE3 was discovered less than a day prior to prior to its closest method.
Based on an observational arc of only 1 day, 2018 GE3 appears to follow an elliptical orbit which stretches from the asteroid belt to deep inside the inner solar system. The moon, by comparison, is roughly 238,900 miles from Earth.