The very first near-Earth asteroid was discovered in the 1800s, and since then, astronomers have been scouring the skies for more.
Over the course of many years, astronomers have continuously found more and more near-Earth asteroids, with researchers reaching a milestone number of more than 30,000 near-Earth asteroids only recently. As equipment increases in quality and accuracy, astronomers are exponentially finding more asteroids. To illustrate this, more than 15,000 near-Earth asteroids were discovered in just the past 10 years. So, are any of these dangerous?
Scientists believe that they have found all asteroids that would cause an extinction-level event if they impact Earth. These asteroids are considered to be "large" near-Earth asteroids (NEA), which means their orbit comes within 120,842,549 miles of the Sun, and their diameter is slightly larger than 1 mile. Researchers report that all of the asteroids of this caliber have already been discovered and that none as expected to hit Earth for at least the next 100 years.
There are still smaller NEAs out there, approximately several hundred feet in diameter, that could cause devastating damage if they hit Earth, possibly wiping out an entire city or, even worse, an entire country. These objects are much harder to spot than their large counterparts as they aren't as bright in the night sky. Luckily, researchers believe none of these smaller, but still large, level of asteroids are expected to hit Earth for the next 100 years.
This leaves us with the really "small" NEAs, and according to reports, there are 1,400 NEAs that have a "non-zero" chance of hitting Earth sometime in the future. While that does sound like bad news, the European Space Agency (ESA), which keeps a log of all NEAs, says that none of these space rocks pose an immediate threat to Earth and that if one or many are found to have a dangerous Earth-colliding trajectory, there will be more than enough time to launch a mission such as NASA's DART to deflect the asteroid off course.
Despite the overall good news that Earth is in no danger for at least the next 100 years from an extinction-level asteroid, it should be noted that researchers are still discovering new asteroids every day, which means there is always the possibility of one popping out of the void that was previously missed.