Several massive asteroids are expected to whiz close to Earth in the coming weeks, including one nearly the size of the Empire State Building.
Two are expected to soar near the planet on Saturday, followed by more in the coming days, according to data from NASA's Center for Near Earth Object Studies.
On Friday, Asteroid 2021 SM3, which has a diameter of up to 525 feet -- bigger than the size of the Great Pyramid of Giza in Egypt -- was projected to zoom by around 3.5 million miles away from Earth, USA Today first reported based off CNEOS data.
Near-Earth objects are defined by NASA as "comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood."
But fear not, though these asteroids are passing relatively close to Earth, they're still a great distance away, experts say.
"Astronomically, these are coming close to the Earth. But in human terms, they are millions of miles away and can get no closer than millions of miles away," Paul Chodas, the director of the CNEOS at NASA's Jet Propulsion Laboratory in Southern California, told ABC News.
The center tracks near-Earth objects for the entire asteroid community so that when close approaches happen astronomers can know where and when and observe their movements.
One of the closest approaches is Asteroid 2021 TJ15, which will pass the Earth at the same distance at the moon, or 238,854 miles away, on Saturday.
"That asteroid has a diameter of 5.6 to 13 meters (18 to 42 feet). That's a tiny asteroid coming to about the distance of the moon. It's still a long, long way, it can't hit the Earth, there's no chance of that," Chodas said.
Asteroid 2004 UE is up to 1,246 feet, nearly the size of the Empire State Building, that will make its close approach Nov. 13 about 2.6 million miles from Earth.
"So that is the size of a small building. That's approaching a medium size. But that's 11 lunar distances approaching sequence, it cannot get any closer than 11.11 lunar distances," Chodas said.
The center has discovered and tracked over 27,000 near-Earth objects. Asteroids range in size with most being small-, medium-size asteroids ranging from 300 meters to 600 meters (984 feet to 1,968 feet) in size and large ones 1 kilometer (3,280 feet) and up in size. He said many of the asteroids that pass Earth are tiny and burn up when they enter the planet's atmosphere.
Unlike the apocalyptic plots in movies, the chances of a massive astroid striking the planet is extremely rare, Chodas said.
"It's simply the fact that there are very fewer medium- and large-size asteroids that come near the Earth to begin with," he said. "There are comparatively few large asteroids. The largest near-Earth asteroid is something like 10 kilometers. But there's only one or two of those."
The asteroids are discovered through observatories, cameras, telescopes and asteroid surveys that search the night sky for movement. After an asteroid is discovered, the center tracks their measurements and locations, and computes an orbit trajectory to predict its future movements to see if there's any chance it'll intersect with Earth.
Just how often do asteroids end up hitting Earth?
"Over the last 20 years of doing this, we've had a total of four asteroids -- tiny, tiny asteroids -- that have been observed in space and headed for the Earth, and have impacted the atmosphere and burned up. They became a bright fireball in each case," Chodas said. "In two of the cases, we've predicted where they would hit ahead of time and predicted where to find the meteorites. Expeditions have gone out and found the meteorites. So our mathematics work pretty well."
One of the most prominent was the Chelyabinsk Event in Russia in February 2013.
"That was the largest observed impact we've had in recent memory, I guess it's a 100-kind of year event. That was a 20-meter asteroid that blazed through the atmosphere over Russia, and it disintegrated. What was started off as a 20-meter asteroid ended up as a core rock that was only one meter across, and it landed in a frozen lake and made a nice round hole in the ice," Chodas said.
So far this year, the biggest asteroid to pass by Earth was Asteroid 2001 FO32, dubbed Apophis the "God of Chaos", in March which was estimated to be 1,100 feet across, NASA said.
Michael Zolensky, an astromaterial curator and researcher at NASA, told ABC News asteroids are " basically leftovers from planet formation."
"Some of them have been whacked and broken by impacts from the other asteroids and then have kind of come back together again, as sort of traveling beanbags of loose rubble," he said.
On Saturday, NASA's newest asteroid probe named Lucy took off from the Kennedy Space Center in Florida for a 12-year mission to study some asteroids known as Trojans around Jupiter.
Lucy will be the first spacecraft to visit these asteroids with the hopes of helping scientists learn more about how our solar system's planets formed and how they ended up in their current configuration, NASA said in a release.