The first asteroidcalled 2016 CZ31, will fly at about 7 p.m. ET (23:00 GMT) on Friday, at about 34,560 mph (55,618 km/h), according to NASA (opens in a new tab). Astronomers estimate that the asteroid is about 400 feet (122 meters) across at its widest point, making it about as wide as a 40-story building is tall. The asteroid will safely miss our planet, passing about 1,740,000 miles (2,800,000 kilometers) from Earth — or more than seven times the average distance between Earth and it moon. According to NASA, this space rock makes close approaches to Earth every few years, with the next one scheduled for January 2028. On Saturday, a second, larger asteroid will pass by our planet, albeit at a greater distance from Earth. This asteroid, called 2013 CU83, is about 600 feet (183 m) across at its widest point and will pass about 4,320,000 miles (6,960,000 km) from Earth, or about 18 times the average distance between Earth and Moon. This colossal space rock will be traveling at 13,153 mph (21,168 km/h) when it approaches Earth at 7:37 p.m. ET (23:37 GMT). Both of these close encounters are much further from the asteroid 2022 NF (opens in new tab), which came within 56,000 miles (90,000 km) — or about 23% of the average distance between Earth and the Moon — on July 7. NASA and other space agencies closely monitor thousands of near-Earth objects like these. Even if an asteroid’s orbit puts it millions of miles from our planet, there is an extremely small chance that the asteroid’s orbit will shift slightly after interacting with gravity of a larger object, such as a planet. even such a tiny shift could potentially put an asteroid on a collision course with Earth on a future flyby. Therefore, the space agencies take planetary defense very seriously. In November 2021, NASA launched an asteroid redirection spacecraft called the Double Asteroid Redirection Test (DART), which will directly hit the 525-foot-wide (160 m) asteroid Dimorphos in autumn (opens in new tab) 2022. The collision will not destroy the asteroid, but it might change the orbital path of the space rock (opens in new tab) slightly, Live Science previously reported. The mission will help test the viability of asteroid deflection should any future asteroid pose an immediate threat to our planet. Originally published in Live Science.