The near-Earth asteroid Apophis (artist’s impression) will fly within 40,000 kilometers of the planet in 2029 – much closer than it came this month.Credit: Detlev van Ravensway / SPL
A space rock 340 meters named Apophis whispered safely past the earth on March 6th. The next time it returns, in 2029, it will not happen that much: Apophis will come within 40,000 kilometers of the planet, skimming just above the region where some high-flying satellites orbit. This will be the first time astronomers can see such a large asteroid passing by so close to us.
Flying past last week gave scientists the chance to test the global planetary defense system, in which astronomers quickly determine the chance that an asteroid could hit Earth if they follow the path across the night sky. “This is a fire drill with a real asteroid,” said Vishnu Reddy, a planetary scientist at the University of Arizona in Tucson, who coordinated the observation campaign.
The Apophis fly-by highlights how much astronomers have learned about near-asteroids – and how much more they need to learn. Since 1998, when NASA began the largest search for asteroids near Earth, scientists have detected more than 25,000 of them. And 2020 was a record year for discoveries. Despite the COVID-19 pandemic that interrupted many of the surveys, astronomers cataloged 2,958 previously unknown asteroids over the course of the year (see ‘Space Tests’).
Source: NASA Center for Near Earth Object Studies
A large number came from the Catalina Sky Survey, which uses three telescopes in Arizona to hunt in threatening spaces. Operations closed short last spring due to the pandemic, and a wildfire in June caused a prolonged closure, but the Catalina survey still discovered 1,548 near-Earth objects. It contains a rare ‘minimoon’ named 2020 CD3, a small asteroid with a diameter of less than 3 meters that was temporarily captured by the earth’s gravity. The minimoon pulled off the earth last April.
Another series of discoveries last year – 1,152 – came from the Pan-STARRS telescopes in Hawaii. The find included an object called 2020 SO, which was not an asteroid, but a remnant of a rocket launcher that has been orbiting space since launching a NASA mission to the Moon in 1966.
Close calls
Some of the asteroids discovered last year came close to Earth – at least 107 of them passed the planet at a distance less than that of the moon. Last year’s near shear included the small asteroid 2020 QG, which ran just 2,950 kilometers above the Indian Ocean in August. This made it the closest known approach – a record that was broken just three months later by another small object, 2020 VT4. The one passed less than 400 kilometers from the planet and was only spotted 15 hours after it whizzed past. If it had hit, it would probably have broken apart in the Earth’s atmosphere.
All these discoveries make astronomers more aware of the billiard ball nature of the solar system, where many asteroids orbit in space near the earth. The recent attempt to observe Apophis highlights how astronomers around the world can work together to assess the threat of asteroids, Reddy says. “It was a big international effort,” he says, “and a lot of fun.” By the time Apophis returns, in eight years, scientists will have an even more detailed census of looming space rocks.