While NASA and other space agencies keep their telescopes trained on near-Earth objects that could smash into us, we don't know how to prevent an impact. Here are some of the best (and weirdest) ideas for protecting Earth from incoming asteroids.
There's actually a federal mandate that says NASA has to discover all near-Earth objects (NEOs) at least 140 meters in size by 2020. The problem is, no one's bothered to fund this mandate, so it's really an impossible job. For the time being, astronomers use existing space observatories to look for NEOs when they can. The Wide-field Infrared Survey Explorer (WISE) just spotted a previously unseen asteroid earlier this week – the kilometer wide rock won't get close to Earth for a few hundred years, but there are plenty more just like it.
If a large asteroid were spotted heading straight for a populated region of Earth tomorrow, what would we be able to do about it? Not much. There's no concrete plan to destroy or deflect a NEO ready to put into action on short notice. Scientists have plenty of ideas, though. Here are some of the best, rated 1-10 on the Michael Bay Explodiness Scale (BES).
Gravity Tractor — BES Rating: 2. Using a gravity tractor to move a large space object would work, but it would be a long, slow, boring process. You simply send the largest craft possible out to the oncoming asteroid and park it next to it (or in orbit around it). With the proper positioning, the gravitational pull of the craft incrementally nudges the asteroid away from its original path, thereby missing Earth. It would take ten years or more, so the key here is early detection. There are rockets involved, and possibly an ion beam, but it's not especially explodey.
Ballast Tether — BES Rating: 1. This another slow, incremental way to change an asteroid's orbit away from an Earth-intersecting path. You send a mission up to the asteroid, and find another asteroid nearby. Then, attach a massive tether connecting the two – and by massive, around 1,000 km would be the minimum. A 100,000 km tether has been proposed. This would make the asteroid and ballast into a "compound object" with a very different center of gravity from the lone asteroid. The difference in gravitational effects would pull them into a different orbit. While not very explodey, this kind of plan feels like it's straight out of a hard sf novel.
Run Away — BES Rating: 10. Government officials refer to this as the Civil Defense plan. You don't try to deflect or destroy the asteroid, you just evacuate the area where it's going to strike. It takes a good evacuation plan, plus the means to deal with potentially millions of refugees. It really only works with small to moderate size NEOs, but it still gets a ten on the Bay Explodiness Scale because it would literally recreate a scene that happened in an actual Michael Bay movie.
Slow Push — BES Rating: 4. This is another deflection idea. Send a big apparatus up to the asteroid, fasten some rockets to it and start pushing. Again, you need to start early to get enough deflection to matter, but at long timescales, you could possibly use ion drives (which, while technologically awesome, are decidedly less explodey than a massive array of rockets).