1.Jupiter, the vacumegravity cleaner of out solar sistem whill suck everything is veary big in his orpit or im himself
2.The asteroide belt:it will stop a lot of big asteroides
3.The Atmospere:will stop all the asteroides
All nations would ally to send as much and as big thermo-nuclear fusion bomb as they can, and pray it will be enough to avoid collision/destroy asteroid ;p
Drink 3 pints of beer, eat some salted pretzels, and don't forget your towel.