13,000 lethal near-Earth asteroids, and what the White House plans to do about them

The Earth is regularly peppered with small, harmless asteroid impacts, but there's an estimated 13,000 giant asteroids, most of which we can't find yet, that could potentially release cataclysmic destruction on the planet. Here's how the White House plans to locate, track, and deflect or destroy them.

Space is a vast, mainly empty expanse, but ours is most certainly not the only giant rock hurtling through it. Earth's orbit frequently crosses paths with asteroids of various sizes – NASA tracked some 556 atmospheric fireballs caused by meteorites between 1 and 20 meters in diameter over a 19-year period between 1994 and 2013.

These were all harmless enough, and indeed the vast majority of near-Earth objects, or NEOs, that enter our atmosphere are small enough to burn up in the atmosphere without causing any problems. But there are plenty of bigger, faster and denser space rocks out there.

Take a look at this incredible compilation of videos of what a single asteroid 20 meters across can do when it hits our atmosphere. The 2013 Chelyabinsk meteor exploded about 30 kilometers above the Earth's surface like a 500-kiloton bomb, releasing nearly 30 times more energy than the Hiroshima atom bomb over a small Russian city. It hospitalized 1,500 people, a remarkably small toll.

Back in 1903, the famous Tunguska impact happened, again over Russia although thankfully in a sparsely populated area. A meteor somewhere over 60 meters wide detonated over a forested area, flattening 80 million trees across some 2,000 square miles of forest. The blast shock, it's estimated, would have measured 5.0 on the Richter scale.

And in relative terms, those two were babies. In the last 10,000 years, we've been hit by at least 8 asteroids that left impact craters more than 100 meters across, including one in Argentina with a 4.5 kilometer diameter.

If you're prepared to go back millions of years, you start finding confirmed impact craters 300 kilometers across. There's some evidence suggesting there's a 600-kilometer wide crater in Australia's Northern territory, and dozens upon dozens of craters more than 20 kilometers wide. These things would have rained utter destruction on everything beneath them, unleashing power many times beyond the scope of the world's entire nuclear arsenal and causing enormous climate and ecological shifts, including mass extinctions and giant glacial melts.

Large meteors will hit Earth again. It's only a matter of time. And while we may have a few technological ideas on how to deflect a big space rock away before it hits us, we still don't have anywhere near a comprehensive set of information about the Near Earth Objects we stand a chance of being hit by.

Cataloguing and tracking these things is no small task. As of December 2016, we know for sure of some 15,342 NEOs between 1 meter and 32 kilometers in diameter. The current estimate is that there are about a thousand out there larger than a kilometer wide, and about 13,000 that are more than 140 meters across – real killers, each with their own speed, direction and orbits through the galaxy.

After two decades of searching, only about 28 percent of the estimated total number of NEOs bigger than 140 meters across have been found and tracked. That's far short of the 90 percent that US Congress directed NASA to get a handle on by 2020, and it leaves a global blind spot of more than 9,000 potential extinction-level threats that we could potentially do something about if we gave ourselves enough warning.

To give you a sense of the scale of the problem, here's a NASA chart showing the orbits of currently known, potentially dangerous asteroids with orbits that bring them close to Earth. The outer ring is Jupiter, and this chart only represents the small percentage of these objects we're currently able to track.

In December 2016, the US White House released its National NEO Preparedness Strategy, a curt 19-page document showing that it understands the problematic potential of NEOs and is working toward addressing it, albeit at the speed of politics.

Enhance NEO detection and tracking capabilities.
Develop methods for deflecting or disrupting incoming asteroids.
Improve modeling and predictions capabilities.
Develop emergency procedures for NEO impact scenarios.
Establish impact response and recovery procedures.
Leverage and support international co-operation.
Establish co-ordination and communication protocols and thresholds for taking action.

Certainly the most urgent aspects would appear to be the first two. In this regard the paper suggests one way to greatly speed up the detection, tracking and categorization of the missing NEOs would be to build a space-based observatory – an exciting possibility for astronomers in and of itself.

In terms of dealing with imminent asteroid collisions, the paper suggests starting out with a fast-response reconnaisance craft that could send back critical information on an approaching NEO's composition, mass and structure to help with decision-making on what the next step should be.

At this point, assuming we've got the time to act, the next step would be to decide whether to try to deflect it, using a "kinetic impactor" that could use fast gravity slingshots and orbital transfers to build up speed and knock the thing off course like a pool ball. This would require very precise aim, as well as high-acceleration maneuvering capability to make sure of a direct hit on a very small, fast-moving target.

For bigger objects or ones that are detected with little time to spare, a "disruption" technique might be the best hope of disaster mitigation. This is an effort to break the asteroid into smaller pieces that might do less harm when they hit.

Either of these ideas will require gigantic amounts of energy, as well as a huge planning, construction and co-ordination effort.

This is obviously a tricky problem in terms of funding. The potential consequences of a decent sized asteroid hit are enormous ... just ask the dinosaurs, who, it's believed, were wiped out by a 10-kilometer wide rock impact that, according to a report by NPR, briefly made the Earth's surface act like a liquid, flinging up a "splash" of rock from as much as six miles below the surface.

On the other hand, the chances of it happening in a given political term are very low. So it's good to know the folks in charge are at least taking this sort of thing seriously.