NASA estimates there are around 4,700 asteroids that are close enough, and big enough, to pose a risk to Earth.
According to CNN, the number of asteroids, give or take about 1,500 is, "how many space rocks that are bigger than 100 meters (330 feet) across and are believed to come within 5 million miles (8 million km) of Earth, or about 20 times farther away than the moon." These asteroids would also be large enough to survive passing through Earth's atmosphere.
Amy Mainzer, an astronomer at NASA's Jet Propulsion Laboratory in California, told CNN, "It's not something that people should panic about. However, we are paying attention to the issue."
More from GlobalPost: Super Earth light detected by NASA space telescope
NASA said a 40-meter asteroid would strike the Earth with an impact comparable to a 3-megaton nuclear bomb, according to CNN. A 2-km asteroid striking Earth "would produce severe environmental damage on a global scale," the space agency estimated, but an impact of that magnitude isn't likely to occur more than twice per million years.
NASA used the Wide-field Infrared Survey Explorer (WISE) as part of the NEOWISE project to find the asteroids. From there they estimated how many more were actually out there.
Of the project Lindley Johnson of the Near-Earth Object Observation Program at NASA Headquarters in Washington, told UPI, "The NEOWISE analysis shows us we've made a good start at finding those objects that truly represent an impact hazard to Earth. But we've many more to find, and it will take a concerted effort during the next couple of decades to find all of them that could do serious damage or be a mission destination in the future."
More from GlobalPost: Supermoon 2012: Did you see it? (PHOTOS)