As per media reports, dated August 18, 2020, a car-sized near-earth asteroid, called, Asteroid 2020QG, made the closest-known approach of 1,830 miles away to the Earth, without colliding with the planet. Researchers did not even know about it until hours after its passage.
It was first observed at the Palomar Observatory, six hours after it passed over the southern Indian Ocean. About 10 to 20 feet in diameter, the asteroid was not actually big enough to pose a serious threat. Had there been a collision, it would have likely ended up as a fireball in Earth’s atmosphere.
The small asteroid approached the Earth from the direction of the Sun and could only be discovered in the night sky by ground-based observatories. As an estimate, there are hundreds of millions of small asteroids the size of 2020 QG, extremely hard to discover because of their distance from the Earth.
It is quite an accomplishment to find tiny close-in asteroids because they pass by quite fast. There’s typically only a short window of a couple of days before or after close approach when this small asteroid is close enough to the Earth to be bright enough. It moves too fast, at 27,600 miles per hour, or nearly 8 miles per second in the sky to be detected by a telescope.