Killer Asteroids and Comets

Near-Earth asteroid, artwork
Science Photo Library - ANDRZEJ WOJCICKI/ Brand X Pictures/ Getty Images

Could a giant space rock hit Earth and destroy life as we know it? It turns out, yes it could. This scenario is not exclusive only to movie theaters and science-fiction novels. There is a real possibility that a large object could one day be on a collision course with Earth. The question becomes, is there anything that we can do about it?

The Key is Early Detection

History tells us that large comets or asteroids periodically collide with Earth, and the results can be devastating. There is evidence that a large object collided with Earth about 65 million years ago and contributed to the extinction of the dinosaurs. Around 50,000 years ago, an iron meteorite smashed to ground in what is now Arizona. It left a crater about a mile across, and sprayed rock across the landscape. More recently, pieces of space debris fell to ground in Chelyabinsk, Russia. An associated shock wave shattered windows, but no other large-scale damage was done.

Clearly these types of collisions do not happen very often, but when if a really big one does come along, what do we need to do to be ready?

The more time that we have to prepare a plan of action the better. Under ideal circumstances we would have years to prepare a strategy on how to destroy or divert the object in question. Surprisingly, this is not out of the question.

With such a large array of optical and infrared telescopes scanning the night sky, NASA is able to catalog and track the motions of thousands of Near Earth Objects (NEOs). Does NASA ever miss one of these NEOs? Sure, but such objects usually pass right by Earth or burn up in our atmosphere. When one of these objects does reach the ground, it is too small to cause significant damage. The loss of life is rare. If a NEO is big enough to pose a threat to Earth, NASA has a very good chance of finding it.

The WISE infrared telescope did a complete survey of the sky and found a significant number of NEOs. The search for these objects is a continuous one, since they need to be close enough for us to detect. There are still some we haven't detected, and they won't be until they get very close so we can see them. 

How Do We Stop Asteroids From Destroying Earth?

Once a NEO is detected that could threaten Earth, there are plans under discussion to prevent a collision. The first step will be to gather information about the object. Obviously the use of ground-based and space-based telescopes will be key, but it will likely extend beyond that. And, the big question is whether or not we are technologically able to do much (if anything) about an incoming impactor. 

NASA will hopefully be able to land a probe of some sort on the object so that it can gather more accurate data about its size, composition and mass. Once this information is gathered and sent back to Earth for analysis, scientists could then develop the best course of action for preventing a devastating collision.

The method used to prevent a cataclysmic disaster will depend on how large the object in question is. Naturally, because of their size, larger objects can be more difficult to prepare for, but there are still things that could be done.

  • Nuclear Bomb: One approach  is divert the object from its course. There are several ways that NASA could do this. The first would be to detonate a nuclear weapon, or some other powerful bomb strategically near the object. The blast would knock the object off course. However, this has to be done carefully because the new course could be equally bad (or worse). 
  • Rocket Motor: Alternatively, a rocket or motor could be attached to the object, and used to drive it onto a new course. In either case, it would not require a significant deviation of course to cause it to miss us, especially if there is an early detection. If launched early enough, a change of course of less than one degree could cause the object to miss the Earth by millions of miles.
  • Solar Sail: Another proposed defense is to use the power of the Sun to help divert the object. The solar energy from the sun can actually apply pressure on an object. So a sail could be attached to the object to harness the solar wind, similar to how we use sail boats here on Earth, and divert the course of the object that way.
  • Break The Object Up: NASA could also use a weapon to break the object up into smaller pieces. In theory this would accomplish two tasks, it would cause most of the pieces to miss Earth by changing their direction. But, more importantly, it would break the object up into such small pieces that even the ones that made it to Earth would likely burn up in the atmosphere. Sounds good in theory, but this would actually be very difficult to do well and would require extensive knowledge of the object and careful planning. This would be most effective on smaller objects.

Obstacles Still Remain

With the previously mentioned defenses in place we should be able to prevent future planet-killing collisions. The problem is that these defenses are not in place, some of them only exist in theory.

Only a very small part of NASA's budget is designated for monitoring NEOs and developing technology to prevent a massive collision. The justification for the lack of funding is that such collisions are rare, and this is evidenced by the fossil record. True. But, what Congressional regulators fail to realize is that it only takes one. We miss one NEO on a collision course and we don't have enough time to react; the results would be fatal.

Clearly early detection is key, but this requires funding and planning that is beyond what NASA is currently being allowed. And even though NASA can find the largest and deadliest NEOs, those 1 kilometer across or more, rather easily, we would need dozens of years to prepare a proper defense, if we can get that kind of time. The situation is worse for smaller objects (those a few hundred meters across or less) that are more difficult to find. We would still need significant lead time in order to prepare our defense. And while collisions with these smaller objects would not create the widespread destruction that the larger objects would, they could still kill hundreds, thousands or millions of people if we don't have enough time to prepare. This is a scenario that such groups as Secure World Foundation and the B612 Foundation are studying, along with NASA. 

Edited and updated by Carolyn Collins Petersen.