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It was a bright stain in the night. On April 27, something caught the attention of astronomers who were carefully studying the data collected by the Pan-STARRS Observatory in Hawaii – a previously unknown event. space rock, and one that was very, very close to Earth.
Coincidentally, the alert came as a fairly large asteroid (called 1998 OR2) was making its closest approach to Earth. That space rock, which was discovered decades ago, is approximately 2.5 miles (4 kilometers) wide. On April 28, he flew across Earth. over a range of about 3.9 million miles (6.3 million km), about 16 times the distance from Earth to the moon. That distance is fairly smooth for Earth flybys; It was the size of the asteroid that made the event intriguing.
It turned out that the Pan-STARRS observation represented the opposite combination of features: A small asteroid and a close flyby shave. The initial sighting sent planetary defense experts around the world into high activity because the first hour of observations suggested that the space rock, now named 2020 HS7, had a 10% chance of colliding with Earth.
Related: Potentially dangerous asteroids (images)
Within an hour, other observatories around the world were also on the case, tracking the object. And as the scientists gathered more measurements, their concerns dissipated: the object was going to safely pass through Earth. These observations also showed that the object was only 13 to 26 feet (4 to 8 meters) wide, suggesting that even if it had collided with Earth, it would simply burn in the the thick atmosphere of the planet.
“Small asteroids like the 2020 HS7 safely pass Earth several times a month,” Lindley Johnson, NASA planetary defense officer he said in a statement released April 28. “It does not pose a threat to our planet, and even if it were on a collision course with Earth, it is small enough for our Earth’s atmosphere to disintegrate it.”
Still, it was an impressively close flyby: According to the European Space Agency (ESA), 2020 HS7 passed 26,550 miles (42,735 km) from the center of the Earth and only 750 miles (1,200 km) from the closest satellite in geostationary orbit, one of the most distant satellite rings that surround Earth. The space rock went under the satellite and left it intact.
According to ESA, the flyby is one of the 50 closest recorded, making it far more interesting to scientists than the much-hyped (and more distant) flyby of the larger 1998 OR2 rock the same week.
Both flybys show the way planetary defense systems they are designed to work: First, identify as many asteroids as possible, starting with the largest. Then track them long enough to trace their orbits. The more data scientists can gather, the more accurate those orbits become, hence the 10% drop probability of impact to a safe failure.
If, on the other hand, more observations show that the probability of impact increases, warning systems are implemented to prepare areas at risk and evaluate possible mitigation approaches, but those systems were not necessary for 2020 HS7.
Email Meghan Bartels at [email protected] or follow her @meghanbartels. Follow us On twitter @Spacedotcom and in Facebook.
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