Sorry, I must challenge a couple of things that beardedbruce has said. First, there most definitely is a systematic effort to identify bodies which might impact earth, and details are given here and here. The primary discovery facility currently is Pan-STARRS. To date 90% of all NEOs bigger than 1km have been discovered, and they are now pushing to smaller sizes. The thing that will clean the statistics up will be the Large Synoptic Survey Telescope which will be operational from 2021.

Second, Bruce says that "the new Emdrive looks promising, but it doesn't because its complete baloney. This is a proposal by a British engineer, Roger Shawyer, for which he once succeeded in getting a government grant. Its been around for years, and has been debunked by both theory and experiment. Basically it is a tapered microwave resonant cavity, and Shawyer's claim is that thrust can be generated by from the electromagnetic field inside. But it can't, except in miniscule quantities. See articles from Greg Egan here, and from John C. Baez, Professor of Mathematical Physics at the University of California, Riverside, here, here and here.