NASA has discovered two asteroids near Earth only after the space rocks safely skimmed past our planet.

2018 NX And 2018 NW

The two tiny asteroids 2018 NX and 2018 NW sneaked past Earth last weekend and were only discovered hours after their flyby. They flew past our home planet at distances of 72,000 miles and 76,000 miles, respectively, or about a third of our distance from the moon.

The International Astronomical Union's Minor Planet Center said that scientists at an observatory on the Palomar Mountain range in California detected the asteroids on Sunday.

Astronomers estimate that the space rocks spanned between 16 feet and 50 feet in diameter. This size is relatively small compared with other near-Earth asteroids.

The space rocks may have passed Earth almost at the same time, but they were not traveling as a pair. Asteroid 2018 NW hurled toward our planet five times faster than 2018 NX.

The duo traveled relatively near Earth, but they did not pose risk because they were far enough not to penetrate our atmosphere.

Asteroid 2018 LA

This is not the first time that an asteroid was discovered only after they passed by close to Earth. Last month, asteroid 2018 LA was discovered just before it hit the atmosphere. The space rock broke into several pieces after it hurtled through space. It eventually fell and lit up the sky over Botswana when it exploded and turned into a fireball meteor.

"The discovery of asteroid 2018 LA is only the third time that an asteroid has been discovered to be on an impact trajectory," said Paul Chodas, from the Center for Near-Earth Object Studies (CNEOS) at JPL. "It is also only the second time that the high probability of an impact was predicted well ahead of the event itself."

Among the reasons why asteroids can be difficult to spot until they are very close are their relatively small size and darkness.

Protecting Earth From Asteroids

Nearby asteroids do not often pose threat to Earth, but space agencies are working on strategies that can help protect the planet from these objects. An asteroid, after all, is blamed for the extinction of the dinosaurs in prehistoric times.

NASA is currently working on the spacecraft called HAMMER (Hypervelocity Asteroid Mitigation Mission for Emergency Response). The spacecraft is intended to crash into a small asteroid to change its course. HAMMER will also use nuclear weapons for big asteroids to divert their trajectory.

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