Earth in the cosmic shooting gallery

NASA released this animation in 2018. It depicts a mapping of the positions of near-Earth objects (NEOs) known at that time. Why 2018? That year marked 20 years of predictions of possible asteroid collisions with Earth, made at NASA’s Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory in Pasadena, California. CNEOS is NASA’s center for computing asteroid and comet orbits and their odds of Earth impact. As the center was about to embark on its third decade, NASA wrote:

Asteroid search teams supported by NASA’s NEO Observations Program have found over 95 percent of near-Earth asteroids currently known. There are now over 18,000 known NEOs and the discovery rate averages about 40 per week.

That’s a far cry from the rate of discovery of these objects in the 1970s, when I first started writing about astronomy. Sure, we knew about asteroids then. And astronomers knew Earth had been subject to asteroid collisions in the past. For example, the one that made the famous Meteor Crater in Arizona.

Earth in the cosmic shooting gallery

But only a few thousand asteroids were known in the 1970s. And astronomers were just beginning to glimpse the potential danger to Earth from these objects. Today, astronomers know over 822,000 known asteroids in total. And about 20,000 of them are now known to be NEOs, with the potential to strike Earth. Fortunately, astronomers have discovered virtually all of the really big asteroids. But several unknown asteroids still sweep past us every year.

The DART mission to the double asteroid Didymos A and B – which yesterday resulted in dramatic imagery of the Didymos B shortly before DART struck it – would have been unthinkable just a few decades ago. But today the mission makes good sense, as a first step in what astronomers call planetary defense. That’s true because, after all, as astronomers in recent years have said, we are indeed living in a cosmic shooting gallery.

Bottom line: Earth in the cosmic shooting gallery: A dramatic animation showing some of the many thousands of asteroids orbiting the sun near Earth.

Via NASA/ JPL