This NASA diagram depicts the passage of asteroid 2012 DA14 through the Earth-moon system on Feb. 15, 2013.
Today's super-close asteroid flyby should be a wakeup call, spurring humanity to keep better track of the millions of space rocks whizzing through Earth's neighborhood, some scientists say.
There's no chance the 150-foot-wide (45 meters) asteroid 2012 DA14 will hit Earth on its closest approach today (Feb. 15) at 2:24 p.m. EST (1924 GMT). But it will cruise within 17,200 miles (27,000 kilometers) of our planet, marking the closest encounter with such a large space rock that researchers have ever known about in advance.
Some scientists hope the flyby serves as a warning shot, reminding folks that Earth sits in a cosmic shooting gallery and that it's just a matter of time before we suffer a major impact — unless we take action.
"This close approach could just as easily have been an impact," Dan Durda, of the Southwest Research Institute in Boulder, Colo., wrote in a blog post Wednesday (Feb. 13).
"With many tens of thousands of undiscovered objects this size roaming our neighborhood, it’s only a matter of time before one of them booms through our atmosphere rather than skating through our planet-circling constellation of satellites," added Durda, who also serves on the board of directors of the B612 Foundation, a nonprofit organization dedicated to predicting and preventing devastating asteroid strikes. [Asteroid 2012 DA14's Flyby: Complete Coverage]
Durda's point was rammed home early Friday morning when a brilliant fireball exploded in the skies over Russia's Chelyabinsk region, which is about 930 miles (1,500 km) east of Moscow. The blast damaged hundreds of buildings and wounded perhaps 1,000 people, according to media reports.
Scientists think the Russian fireball was caused by an object weighing about 7,000 tons. For comparison, 2012 DA14 tips the scales at about 140,000 tons. The two space rocks are completely unrelated, NASA researchers said.
Millions of space rocks
Earth has been pummeled by asteroids throughout its 4.5-billion-year history. Perhaps the most famous impact came 65 million years ago, when a 6-mile-wide (10 km) behemoth smashed into our planet and wiped out the dinosaurs.
The good news is that another such catastrophic impact does not appear to be in the offing anytime soon. NASA researchers have mapped out the paths of more than 90 percent of the near-Earth asteroids at least 0.6 miles (1 km) across, which could threaten human civilization if they hit us. Not one is on a collision course with our planet in the foreseeable future.
But the numbers get worse from there. Observations by NASA's WISE space telescope suggest that about 4,700 asteroidsat least 330 feet (100 m) wide come uncomfortably close to our planet at some point in their orbits.
So far, astronomers have spotted less than 30 percent of these large space rocks, which could destroy an area the size of a state if they slammed into Earth. And they've identified just 1 percent of the objects that are about the size of 2012 DA14 or bigger, B612 officials have said.
Such asteroids are capable of inflicting serious damage on a local scale, as the "Tunguska Event" illustrates. In 1908, a 130-foot-wide (40 m) asteroid exploded over the Podkamennaya Tunguska River in Siberia, flattening about 825 square miles (2,137 square km) of forest.
Astronomers think, all together 1 million or more near-Earth asteroids are out there, cruising silently through the dark depths of space. About 9,600 have been discovered to date.
"It is actually difficult to look for these things," said Paul Dimotakis of Caltech in Pasadena, who is part of a team studying the feasibility of capturing and retrieving a near-Earth asteroid for future study and potential use.
Dimotakis notes that it's tough to spot asteroids between Earth and the sun, because the star's glare drowns out the relatively tiny objects from our perspective here on Earth. So researchers often point their instruments in the other direction, spotting more-distant space rocks that generally pose less of a threat. The ones that likely hold more potential risk are left in the dark of sorts.
"It's like the man who lost the keys and is looking where there is light, not where the keys were lost," Dimotakis told SPACE.com. [The 7 Strangest Asteroids in the Solar System]
New space telescope needed
Dimotakis says humanity should place an asteroid-hunting telescope near the orbit of Venus, where it could look outward and scan Earth's neighborhood without having to fight the sun's overwhelming glare.
The B612 Foundation agrees and is working to make it happen. The organization is developing a space telescope called Sentinel, which is slated to launch in 2017 or 2018 and eventually settle into a Venus-like orbit around the sun.
In 5 1/2 years of operation, Sentinel should find about 500,000 near-Earth asteroids, including all of the remaining mountain-size space rocks that could potentially end civilization and roughly 90 percent of the asteroids big enough to wipe out an entire state, B612 officials have said.
The main goal is to spot the really dangerous asteroids decades before they may hit us, giving humanity plenty of time to mount a deflection mission— for example, to launch a gravity-tractor probe that would fly alongside the asteroid for years, nudging it off course via a tiny gravitational tug.
"Rather than playing the odds of time, wouldn’t it be far better to be able to know, with some reasonable certainty, that we’ve cataloged the entire population of potentially hazardous asteroids?" Durda wrote. "With such a catalog in hand, we'd either know we're safe from disastrous impacts for the foreseeable future or at least be able to plan ahead for any known to be on our near-term cosmic planning calendar."
Editor's note: If you snap a photo of asteroid 2012 DA14, or any other amazing night sky object, and you'd like to share it for a possible story or image gallery, please send images and comments to managing editor Tariq Malik at email@example.com.
This story was updated at 5:00 p.m. EST to give a revised estimate of the weight of the object that caused the Russian fireball.