Intercept an Asteroid?

The US government pays people to think of disasters that might befall us and to then dream up how we might avoid or mitigate those disasters. One kind of disaster that has caught their attention is the possibility of a large asteroid crashing into Earth. Such an impact could be catastrophic if the asteroid is large enough, so the People’s Republic of China and the United States of America are each working on plans to alter the course of an approaching asteroid in time to make it miss the Earth. But is the problem serious enough to be worth the effort?

Consider the small asteroid that entered the atmosphere and exploded over Chelyabinsk, Russia in 2013. It was estimated to be about 20m in diameter with an entry velocity of about 19 km/sec. Since it entered the atmosphere at a flat angle, it overheated and exploded rather than crashing intact into the ground. The energy released was estimated at the equivalent of about 400-500 kilotons of TNT; much larger than either the Hiroshima or Nagasaki atomic bombs.

The asteroid that exploded over Chelyabinsk was not detected before it entered the atmosphere. NASA was tracking another asteroid approaching on a near-miss path, and that asteroid passed the Earth as projected a few hours after the Chelyabinsk explosion. This illustrates a challenge even trickier than diverting an incoming piece of rock: how to know that it is coming in time to do anything about it?

The chart below comes from one of my favorite astronomy web pages: spaceweather.com The page authors update this chart every day, and it illustrates two items of interest for sake of this discussion. First, as the chart header notes, astronomers are finding new potentially hazardous asteroids all the time. This chart comes from July 4, 2021; earlier today the tally was up to 2200. Second, notice the date when Asterooid 2021_NA missed the Earth by 0.2 LD (see the chart footnote for explanation). Asteroid 2021_NA missed Earth by 20% of the distance between the Earth and the Earth’s Moon. No big deal, except that the asteroid did not show up in the chart until the day after the near miss. And this is the norm: many if not most near-miss asteroids may not be detected until at the last minute. It does not do much good to be able to deflect an asteroid if you don’t see it coming.

So what is the point? You can 1) take this as an interesting technical challenge, 2) let it keep you awake at night with worry, or 3) don’t worry about it. My approach is a combination of 1) and 3), and mostly 3). After all, as Jesus said, “I say to you, do not be worried about your life, as to what you will eat or what you will drink; nor for your body, as to what you will put on. Is not life more than food, and the body more than clothing? Look at the birds of the air, that they do not sow, nor reap nor gather into barns, and yet your heavenly Father feeds them. Are you not worth much more than they? And who of you by being worried can add a single hour to his life? And why are you worried about clothing? Observe how the lilies of the field grow; they do not toil nor do they spin, yet I say to you that not even Solomon in all his glory clothed himself like one of these. But if God so clothes the grass of the field, which is alive today and tomorrow is thrown into the furnace, will He not much more clothe you? You of little faith! Do not worry then, saying, ‘What will we eat?’ or ‘What will we drink?’ or ‘What will we wear for clothing?’ For the Gentiles eagerly seek all these things; for your heavenly Father knows that you need all these things. But seek first His kingdom and His righteousness, and all these things will be added to you. So do not worry about tomorrow; for tomorrow will care for itself. Each day has enough trouble of its own.” (Matthew 6:25-34, NASB)