A small, harmless space rock turned into a fireball in our atmosphere. What's unusual is that astronomers saw it beforehand.

An asteroid the size of a refrigerator was spotted by telescopes in Hawaii on Saturday, just before it collided with Earth's atmosphere and burned as a fireball in the sky due south of Puerto Rico. The harmless space rock, officially named 2019 MO, never had a chance of making it to the ground or doing much damage, as it was only about a tenth the size of the bolide that exploded in the atmosphere over Russia in 2013. 

According to fireball and bolide data from NASA, our atmosphere is struck by a meteor this size or larger roughly once a year. 

What's most interesting about 2019 MO, though, is the fact that it was spotted by telescopes beforehand. That's only happened four times in history, according to Italian amateur astronomer Ernesto Guido.

The other three times all happened in the last 12 years, including asteroid 2018 LA that made it all the way to the ground in Africa. 

This doesn't mean space rocks are getting more aggressive in the 21st century, but that astronomers' equipment and techniques are getting better at spotting incoming asteroids.   

According to the International Astronomical Union's Minor Planet Center, 2019 MO impacted the atmosphere at around 5:30 p.m. EDT Saturday. 

Astronomer Peter Brown from Western University in Ontario noted that the impact was recorded at the equivalent explosive power of 5,000 tons of TNT. 

Of course, the same-day notice provided in the case of 2019 MO wouldn't be too helpful in making preparations if it were a much bigger asteroid smacking into the sky. Fortunately NASA and other agencies have mandated goals to work toward tracking as many of the biggest rocks out there as possible. 

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