So what do we do? The first thing is to track and record all the near-Earth objects, which is already underway with many projects across the globe and in space. Years ago, Congress required NASA to track 90 percent of objects one kilometer and over, which was accomplished as of 2011 — but smaller ones are still being racked up by the thousands. All told, nearly 20,000 near-Earth objects have been found at time of writing. Meanwhile, NASA’s Jet Propulsion Laboratory has an automated system to detect which objects are a threat.
Then once every threatening object is tracked, we just need a way to deflect them. Laser light might exert enough pressure if it was caught early enough, as you’d only have to change the trajectory by a tiny bit. (This calls for extreme accuracy, as you don’t want to accidentally deflect something into the planet.) You could accomplish the same thing with a probe’s gravity — or you could crash the probe into it at high speed. Indeed, NASA is planning to launch a test probe for just this purpose in 2020 or 2021.