There are countless amount of asteroids floating about in space, and it's NASA's job to track the ones that are potentially dangerous to Earth.
Luckily, NASA believes it is tracking the large ones that could be a threat to our planet, as there aren't as many of those as the smaller ones that would burn up in our atmosphere if their trajectory lined up with Earth. Additionally, asteroids make "close" fly-by's with Earth quite regularly, and two will be doing that very soon. On its Jet Propulsion Laboratory website, NASA states that Asteroid 1998 SD9 and Asteroid RP12 will be making their closest approach to Earth on October 6.
Originally discovered in 1998, asteroid 1998 SD9 will arrive at 3:53 p.m. ET and will be traveling at a speed of 24,606 mph. 1998 SD9 is anywhere between 144 to 325 feet in diameter, or approximately the size of an airplane, according to NASA. Additionally, 1998 SD9 will be within 2,530,000 miles of Earth. Asteroid RP12 is slightly smaller than 1998 SD9 at around 104 to 256 feet in diameter, but it will pass closer - within 1,200,000 miles of Earth. RP12 will pass Earth at around 21,000 mph.
If you are interested in learning more about asteroids, check out this link here.