spaceSpace and Physics

A Space Rock The Size Of A House Whizzed Past Earth Today - And We Only Discovered It Last Week


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockDec 28 2017, 18:50 UTC


A house-sized asteroid flew past our planet today at about 58 percent the distance between the Earth and the Moon. The object, known as 2017 YZ4, is estimated to be between 7 and 15 meters (23 and 49 feet) – slightly smaller than the Chelyabinsk meteor that exploded over Russia in 2013.

2017 YZ4 was only discovered on Christmas Day by the Mount Lemmon Survey, which is one of the most successful detectors of near-Earth objects (NEOs) in the world. 2017 YZ4 is an asteroid in the Apollo family, a group characterized by orbits that are wider than Earth’s but fly closer to the Sun than our own planet.


The asteroid’s closest approach happened around 10:56 Eastern Time at 224,396 kilometers (139 433 miles) from the surface of our planet. This is a safe distance, not that we could do much about it since it was only discovered a few days ago. It has a speed of 9.5 kilometers (5.9 miles) per second relative to our planet, so you wouldn’t want to be on its path.

This is 2017 YZ4 orbit around the Sun. NASA

According to NASA’s Center for Near Earth Object Studies, this was the closest asteroid since 2017 WA14 approached Earth on November 21. In 2017, there have been another 51 objects that ended up flying within one lunar distance. All but one, 2012 TC4, were discovered this year as they were approaching our planet.

NASA and other space agencies used 2012 TC4 to study the asteroid in detail. They even ran tests to better understand our asteroid warning systems and to determine how capable we would be at fighting off these objects.


While 2017 YZ4 might not pose an extinction-level threat to our planet, we need to remain vigilant as these objects can create widespread damage, like the above-mentioned Chelyabinsk meteor whose shock wave broke windows and injured thousands. For this reason, NASA and the European Space Agency have projects monitoring NEOs.

So far, we have discovered just a small percentage of the estimated 1 million hazardous asteroids larger than 30 meters (100 feet) that populate the space around Earth. Only about one in four asteroids larger than 100 meters (328 feet) have been discovered.

Teams are trying their best to come up with the right tools to protect us against this unlikely but serious threat; however, we currently remain woefully unprepared.

spaceSpace and Physics
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  • 2017 YZ4