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Teams tracked around 3,000 asteroids passing close to Earth in 2020 alone. More than ever before. Knowing their nature and pathways is important. Because an impact can be devastating.
On March 6, 2021, Apophis, a 340-meter-long space rock, raced past the earth. Without consequences. The next return in 2029, however, may be more eventful. Because Apophis will approach the planet up to 40,000 kilometers and thus touch the region in which some high-flying satellites orbit. For the first time, astronomers will be able to see an asteroid of this size fly so close to us.

Thanks to the flyby in early March, teams were able to test a global planetary defense system. It is used to estimate the probability of an object hitting the earth while astronomers are still tracking its path in the night sky. "It was a fire drill with a real asteroid," says Vishnu Reddy, planetary researcher at the University of Arizona in Tucson, who coordinated the observation campaign.
Apophis's visit shows how much astronomers have learned about near-Earth asteroids in recent years. But also how much they still have to learn. Since NASA began its largest search for near-Earth asteroids in 1998, teams have identified more than 25,000 of these objects. 2020 was a record year for discoveries. Despite the Covid-19 pandemic , which interrupted many of the surveys, a total of 2958 previously unknown near-Earth asteroids were cataloged over the course of the year (see "Lumps of space").
In 2020, teams found more near-Earth asteroids than ever before, as the bar chart shows.
Much of it comes from the Catalina Sky Survey, which uses three telescopes to search for threatening space rocks in Arizona. Although operations were temporarily suspended in spring 2020 due to the pandemic and a forest fire in June resulted in a prolonged closure, the Catalina Survey discovered 1,548 objects near the earth. Among them was a rare minimoon called 2020 CD3. The tiny asteroid, less than three meters in diameter, was temporarily captured by Earth's gravity. Last April, the minimoon withdrew from gravity again.
Another set of discoveries in 2020 - 1,152 pieces - is from the Pan-STARRS Surveying Telescopes in Hawaii. Among the finds was an object named 2020 SO, which turned out not to be an asteroid, but rather a leftover rocket booster that has been floating around in space since the start of a NASA mission to the moon in 1966.

Flyby less than 400 kilometers away

Some of the asteroids discovered in 2020 came quite close to Earth from a cosmological point of view - at least 107 of them passed the planets at a distance less than that of the Moon. One of the special features of the year was the tiny asteroid 2020 QG, which flew just 2950 kilometers over the Indian Ocean in August. It was the closest known approximation - a record broken by another small object just three months later. The 2020 VT4 passed the planet less than 400 kilometers away and was not seen until 15 hours after it passed. Had the course been different, 2020 VT4 would likely have broken apart in the earth's atmosphere.
All of these discoveries make astronomers more aware of the billiard ball nature of the solar system, in which a multitude of asteroids float around in near-Earth space. The latest foray into the observation of Apophis shows how astronomers around the world can work together to assess the threat posed by asteroids, Reddy says. "It was a huge international effort," he says, "and a lot of fun." When Apophis reappears in eight years, the scientists will have an even more detailed count of the threatening space rocks.

Source: spektrum