We can now shoot asteroids and actually make a dent, but maybe not for the reason you think.
The Japanese Aerospace Exploration Agency (JAXA) just announced that it's developed a cannon that can shoot a hole in an asteroid, and the device has been successfully tested and will be launched into space next year. Finally, mankind will be able to stare down a massive hunk of space rock and fearlessly blast it with a space gun. Someone get Bruce Willis on the phone.
Unfortunately, the cannon is actually not designed to destroy asteroids hurtling toward Earth. It was built for purely scientific purposes. Next year, the device will be mounted on Japan's Hayabusa 2 probe, which will be sent to rendezvous with 1999JU3, an asteroid between Earth and Mars. Once there, the probe will drop the device and hide behind the asteroid, while the cannon uses an explosion to propel a four-pound projectile at the asteroid, knocking a hole in its surface. The probe will then come back around to the newly created asteroid wound, scoop out some of the debris and return to Earth. It's all documented in the rather nifty simulation video above.
The idea here is to gather information from the inside of the asteroid that you can't get by simply viewing the exterior. This particular asteroid was chosen because researchers believe it hasn't changed much since it formed, so they're hoping its innards will hold water or other material that give clues as to what the early formation of our solar system was like. If the launch goes according to plan, the cannon will shoot the asteroid in 2018, and the probe will return to Earth by 2020, so maybe by then we'll have a whole mess of exciting new asteroid data.
So, sadly, humanity has not yet devised a gun that can obliterate asteroids, videogame-style, but we do get some interesting space research out of this invention. Plus, it would probably still be a lot of fun to pull the trigger on this thing.