Incoming asteroids conjure images of the world cracked apart, but that’s not always the case. The world got a shock on June 2nd, 2018, when a small space rock, about six feet long, plunged into Earth’s atmosphere, detonating spectacularly over South Africa. Given that the explosion was several miles above land, no one was ever in any danger. In fact, Catalina Sky Survey, on the outskirts of Tucson, Arizona, were the first sky-watchers to see the asteroid. The incoming space rock was very dim, due to its dark coloration and tiny size, just under 7 feet long. It’s amazing that scientists were able to detect such a tiny piece of stellar flotsam, but also a bit chilling, given that only hours later it struck the Earth’s atmosphere. That rock did no damage, but will we always get lucky?
The simple answer is no. We won’t.
An asteroid’s potential for destruction is related to its size, composition, and speed. Size of the rock is always critical, but in composition, asteroids come in three categories. Type M are composed of metals, mainly iron and some of the platinum group of metals. Type C, the carbonaceous chondrite asteroids, are made up of metal, organic compounds, and water. These asteroids tend to be quite dark on their surfaces. They’re problematic in that their very low reflectivity makes them challenging to detect. Type S the NASA maintains a skywatch program, cataloguing near-earth asteroids (NEAs) 460 feet and above. An asteroid of that size would be disastrous if it stuck near a city, but wouldn’t cause mass extinctions. However, a direct hit on a populated area would cause many deaths. much like a nuclear warhead. An ocean collision would result in giant tsunamis.
Around 1500 feet and up, an asteroid impact would cause regional disaster on the scale of a devastated continent. After 3000 feet and above, we’re talking about an extinction level event. The asteroid that killed the dinosaurs was around 6 miles long.
Slowing Down Doom
In the case of potentially dangerous earth-crossing asteroids, being forewarned is literally forearmed. The further away from earth a dangerous body is, the more time scientists have to determine what to do. Without enough lead time, there won’t be anything to do at all if an asteroid or comet is large and has low reflectivity (low albedo). A positive takeaway is that NASA believes they have all the dangerous near-earth asteroids mapped out. If that’s so, then our chances of dodging a fatal rock are pretty good. In fact, no known asteroid poses a significant threat of impact for over a century. The catch is “known.” There’s always the potential for a nasty surprise.
NASA has two plans to stop an asteroid from hitting the earth. An impactor approach involves striking the asteroid with an object propelled at high speed. The idea isn’t to shatter it, but to slow it down. Asteroids move around 12 miles per second, so introducing even a small but incremental slowdown would allow the earth to sail on unimpeded. The other technique would involve placing an extremely heavy mass in a close, but fixed position near the asteroid to pull it off course enough to miss the earth. The most important thing we can do is catch a dangerous incoming rock as soon as possible. Neither of these techniques would work with less than several months–or years—of forewarning.