A 20 meter wide asteroid exploded over Chelyabinsk, Russia last year and got the world’s attention with a 500 kiloton explosion equivalent to 25 Hiroshima atomic bombs. Seven thousand buildings were damaged and 1500 people were injured, most of them by flying glass. The asteroid was not known beforehand because it approached from the direction of the sun—on the Earth’s day side where it couldn’t be seen. Fortunately it exploded at high altitude, almost 30 kilometers up, so that a lot of the energy was absorbed by the atmosphere. (The resulting pressure wave circled the Earth more than once.) This helps account for the fact that no one was killed. Another thing that reduced the damage was the shallow approach of the trajectory: the asteroid almost skimmed the atmosphere. If it had come in close to vertically over the city, there likely would have been much more damage and many casualties.
Recently (2014/09/07), another Chelyabinsk sized asteroid (a little smaller, 13 meters wide) skimmed by Earth on a trajectory just outside our geosynchronous satellite orbits. In the astronomy world of asteroid encounters, this was an incredibly close call. Unlike the Chelyabinsk asteroid, this one was found a few days before the event because it approached from the opposite direction—opposite the sun, on the night side of Earth. However, if it had been on a predicted impact course over a populated area, a few days lead time would be insufficient to do much more than alert the population and perhaps evacuate the area. Fortunately, most impacts like this would be over unpopulated regions like the ocean.
NASA estimated in 2012 that there are 4,700 potentially hazardous asteroids larger than 100 meters that could pose a danger to Earth. About 70% of these hadn’t even been discovered. However, we (our world-wide astronomical community and NASA in particular) seem to have pretty good automated discovery programs going that chip away at that percentage pretty fast. NASA set a goal in 2008 of discovering 90% of potential threats over 140 meters, and that may happen by 2020, leaving us with only 10% to worry about.
Some of the discovery programs are the Catalina Survey near Tucson, Arizona and the Pan STARR program on Mt. Haleakala in Hawaii. Then there’s the Atlas program, also Hawaii, funded by NASA, starting up next year with two telescopes covering the entire sky several times every night. After that, there’s the B612 Foundation, a private organization partnering with NASA and others; they plan to launch an infrared satellite named Sentinel by 2018 and put it into a Venus-like orbit inside Earth’s orbit so it can find objects in regions poorly seen from Earth.
The main thing we’re lacking, though, is an asteroid defense system. We’re studying ideas about how to deflect dangerous asteroids, but we don’t know whether any of these things would work because we haven’t tested them in space. If we want to be proactive and get ready for a low probability event that could have massive consequences, we’d have to actually build some spacecraft and send them out to asteroids and try out some of these methods.
That would cost a lot of money. Taxpayer money. That would require political decisions. These are things that are in short supply in today’s political climate.
So there’s the question: We’re willing to spend lots of collective money on low probability events like winning a lottery; we spend a lot of money keeping the odds of airline accidents low; are we willing to spend some money on keeping the world safe from asteroids? Or do we say “Don’t fix it if it ain’t broke,” or “Let sleeping dogs lie,” or “Never worry about a disaster until after it happens,” or some of those other non-proactive things?
What do we do about it? That’s the question The Darkest Side of Saturn asks and answers in an alternate universe. That’s probably the question we ought to answer in our particular universe.