An asteroid between 50 and 130 feet wide will fly by the Earth on Friday on a path closer than the moon's, NASA said this week.
Asteroid 2018 CB is the second small asteroid to buzz by the planet this week, according to NASA.
"Asteroids of this size do not often approach this close to our planet -- maybe only once or twice a year," said Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA's Jet Propulsion Laboratory in Pasadena, California.
NASA said 2018 CB will safely pass the Earth at a distance of 39,000 miles, pretty close by space standards.
On Tuesday, 2018 CC was about 114,000 miles away when it flew by Earth.
The moon is an average of 240,000 miles from Earth.
NASA detects about 1,500 new near-Earth objects a year. Small asteroids pass between the planet and the moon several times a month.
Earth isn't at significant risk of getting hit by any known asteroid for at least 100 years.