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"  You&amp;#039;re about 60 miles away from the impact site when you happen to glance up. You see a blindingly bright fireball streaking through the sky. Then, what looks like a beautiful sunrise\u2014except it gives you instant first-degree burns. You feel the ground shake, possibly hard enough to knock you off your feet. You&amp;#039;re pelted with chunks of earth and rock the size of walnuts\u2014debris from the newly created 4-mile-wide crater. Five minutes later, there&amp;#039;s a blast of air so fierce that it blows out windows in your house, accompanied by a noise like a monstrous sonic boom.  &amp;quot;Then, well, various kinds of panic would ensue,&amp;quot; says Jay Melosh, an expert in impact craters at Purdue University in Indiana. Melosh described the scenario above, which is what he says would happen if an asteroid like the aircraft-carrier-size 2005 YU55\u2014which will make a close pass of our planet today\u2014smashed into Earth. Fortunately, 2005 YU55 will whiz harmlessly past us tonight\u2014it will be closest at about 6:30 EST. The largest asteroid to come this close in decades, 2005 YU55 will pass between Earth and the moon&amp;#039;s orbit, coming within 201,000 miles of us while traveling at a speed of 8 miles per second. An actual collision wouldn&amp;#039;t be new to our planet, however. &amp;quot;They&amp;#039;re not terribly unique,&amp;quot; Melosh says. Statistically speaking, something the size of 2005 YU55 plows into the planet about once every hundred thousand years. &amp;quot;It&amp;#039;s a random process,&amp;quot; Melosh says. &amp;quot;We could get hit by something like this in 15 years, or it may be 200,000 years.&amp;quot; Every five Earth years, 2005 YU55 completes four circuits of its elliptical orbit around the sun, so it will continue to pass Earth fairly frequently. Experts don&amp;#039;t expect it to be close enough to hit us anytime this century, though.  Predicting Impacts Astronomers can now predict the path of an asteroid decades in advance with a high degree of confidence. But despite the sophisticated physics used to calculate their future paths, asteroids still remain somewhat elusive.  Part of the reason is that objects in space are always pulling on one another, subtly changing each other&amp;#039;s orbits. On any given pass, if an asteroid passes close enough to anything with enough gravity, it will get pulled from its original path a tiny bit. Consider the phenomenon called the gravitational keyhole, a sort of un-sweet spot in space: If a near-Earth asteroid passed through one, the asteroid would get pulled off-course in just the way necessary to send it on a collision course with Earth.  A small error in our calculations of an asteroid&amp;#039;s track means that, should the asteroid pass through a gravitational keyhole, it could throw off scientists&amp;#039; predictions. &amp;quot;Any tiny uncertainty gets magnified,&amp;quot; says Dave Hyland, an expert in asteroid mitigation at Texas A&amp;amp;amp;M University. In 2029, Hyland says, 2005 YU55 will pass close enough to Venus that the planet will slightly alter its path. But the chances it will get thrown toward Earth are slim, especially because scientists have a good handle on 2005 YU55\u2014it made a relatively close pass by us on April 19, 2010, allowing radar to nail down its orbit.  Earth received a bigger scare a few years ago. Another asteroid, called Apophis, was given a frightening 1-in-100 chance of striking Earth at the time of its discovery in 2004. Since then, as data collection has improved, the odds of a collision on its next pass in 2026 have dropped significantly, Hyland says. &amp;quot;When it does fly by Earth, it&amp;#039;s going to be within five or six Earth radii from us, and the Earth will perturb its orbit quite significantly\u2014by about 20 percent,&amp;quot; he says. Of course, this doesn&amp;#039;t necessarily mean it will pass through a keyhole and head our way\u2014the chances of that happening are less than one in a quarter million, and dropping steadily. Watching the Skies As of September, scientists are tracking 90 percent of all objects larger than a kilometer, or six-tenths of a mile, in diameter, Melosh says. But other experts don&amp;#039;t think this is enough. Ed Lu, a physicist and former NASA astronaut, is a founding member of the B612 Foundation, an organization with the aim to &amp;quot;predict and prevent catastrophic asteroid impacts on Earth.&amp;quot; The kilometer-wide asteroids scientists are currently tracking would wipe out civilization\u2014immediately. However, Lu warns, a smaller asteroid could also cause devastation. A small asteroid that smashed into a Western Europe, for example, could have crushing repercussions for the world economy. &amp;quot;We should set our sights a little higher than simply protecting ourselves from &amp;#039;civilization-enders,&amp;#039;&amp;quot; Lu says.  According to Lu, scientists are tracking only 1 percent of these kinds of asteroids. &amp;quot;We&amp;#039;re basically flying around the solar system with our eyes closed,&amp;quot; he says. His solution: Put a $500 million infrared telescope in space that could track these smaller, but still deadly, wanderers.  Give It a Little Shove Scientists like Lu are already considering the next step: what to do if they found out a big space rock was coming our way. The Hollywood idea of blowing up the asteroid is probably more sci-fi than science. &amp;quot;Let&amp;#039;s say you have a big rock on a hill above your house,&amp;quot; Lu says. &amp;quot;You don&amp;#039;t want to blow it up and just hope that one of the pieces doesn&amp;#039;t hit you.&amp;quot;  A better technique would be to nudge the asteroid out of the way. Lu says that the easiest thing to do is probably hit the asteroid with a small spacecraft. Other techniques include using the gravity of a spacecraft to gently pull the asteroid out of its path toward Earth. And one more big idea, courtesy of Hyland: painting the asteroid with reflective paint to modify the natural asymmetry known as its albedo. That would change how much sunlight it reflects, and then change its course, because sunlight pushes on objects very slightly. Of course, these techniques are only useful if we know about the asteroid far in advance. Subtle but precise approaches like the gravity tractor approach require a long lead time to work, so that a tiny push has time to move the asteroid far off its course. &amp;quot;You have many options, as long as you&amp;#039;ve tracked them,&amp;quot; Lu says. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/space/deep-space/a7216/death-by-asteroid-and-how-to-avoid-it-6551740/>