On Jan. 13 an asteroid whizzed past, buzzing us at only a third of the distance to the moon. If its course had taken it into the atmosphere, the air burst would have been somewhere between 2.8 times and 7.7 times the force of the atomic bomb that destroyed Nagasaki.
But don’t fret about it too much. “Those who study the complex interplay of cause and effect in the history of the Universe,” The Hitchhiker’s Guide to the Galaxy cheerfully points out, “say that this sort of thing is going on all the time.”
More to the point, asteroids of this size — between 33 feet (10 meters) and 49 feet (15 meters) across — pass within one lunar distance of Earth every week, and we haven’t lost any cities to asteroids lately.
The figures are derived from the Internet site Earth Science Picture of the Day, which on Saturday posted a dramatic video of the asteroid’s near pass, taken by Patrick Wiggins, NASA solar system ambassador to Utah.
The movie, located HERE, shows the space rock hurtling past the stars, which are rendered as streaks. They’re streaks because each exposure was 15 seconds long while his telescope tracked the asteroid. As the scope kept the minor planet in view, the asteroid whisked past the background stars. Altogether, Wiggins shot 30 photos, which were strung together to make the movie.
Kurt Fisher and Wiggins, both members of the Salt Lake Astronomical Society, wrote the caption, which explains that the asteroid, “2010 AL30,” is among several thousand similar near Earth objects. NEOs, which could be comets or asteroids, have paths that cross Earth’s orbit, making them potentially dangerous. Or deadly. Or devastating, if you’re a dinosaur living 65 million years ago.
That’s why NASA is vigorously tracking NEOs and is extending its search to smaller and smaller objects.
“NASA’s NEO program estimates that ‘with an average interval of about 100 years, rocky or iron asteroids larger than about 164 ft (50 m) would be expected to reach the Earth’s surface and cause local disasters or produce the tidal waves that can inundate low lying coastal areas,'” the caption notes.
The authors say an NEO 50 meters (164 feet) across “can create a blast equivalent to one megaton of TNT.” A megaton blast is equal to that of 1 million tons of the explosive. Fisher and Wiggins write that the Nagasaki bomb’s explosive yield was an estimated 15 to 18 kilotons; one megaton is 1,000 kilotons.
“There have not been a significant number of deaths caused by asteroids in historical times due to the infrequency of the major events. When such events do occur they are more likely to happen over unpopulated regions such as oceans,” they add.
The unlikely does happen — as evidenced by huge scars scattered throughout Earth. The nearest large one is the Arizona Meteor Crater, near Winslow, the eroded remains of which are almost a mile across and 550 feet deep. Around 50,000 years ago, that NEO didn’t just come near; it slammed in, producing a 20-megaton blast.
If astronomers detect a big rock racing toward Earth, could they blow it up? “It goes from being a single shot to basically a shotgun approach. So rather than a big explosion you get a lot of small ones, probably lethal ones,” Wiggins told Nightly News.
Our best hope is that someone will notice it while it’s far enough from Earth to be diverted. Methods proposed include nudging it with a rocket or even using a large spacecraft’s gravity to pull it into a harmless course. “The farther out you find them, the less effort it takes to redirect them,” he said. “If you get a tiny push, the cumulative effect over years and even decades is going to be a great deal.”
The latest count of space rocks, most of them not NEOs, is around 500,000, he said. Meanwhile, Earth sucks in hundreds of tons of tiny space debris every day, doing no harm to the inhabitants.
By no means are all such objects plotted. “We don’t find them all.”
Still, given the rarity of big asteroid strikes, Wiggins said, “This really is not the kind of thing that makes me worried.”