Monday, November 16, 2015

Some back of the envelope calculations....

In the last year 156 objects floating through space came within 5ld of Earth.  So if we look at this in a simplified 2 dimensional sense if we have a dart board 5ld in radius with the Earth at the center, that dart board got hit 156 times.

The total area of the dart board is:

5ld squared pi, converted to square miles....

1.25 million squared pi


~5 e12 square miles.

the area of the earth disk in the center would be

4,000 miles squared pi

or 5 e7 square miles

By these calculations we know of an object that should hit us about 1 in 100000 years.  Since we know that the Earth gits hit by shit more often than that we have a lot of work to do on our space program.


  1. Sure but does this take into account the effect of Earth's gravity on these other objects? It also doesn't help that the system is not 2 dimensional at all. There is a lot more exposed surface area on a ball than there is on a flat circle.

  2. Ok, you are getting off the back of the envelope. Once you start looking at the perturbations of gravity on objects passing by at various ranges at 20km/s you might as well look at the detection limits of modern observation and the sizes of objects detected at range to estimate the percentage missed, as whether we will ever detect objects passing by on the daytime side of Earth. I was using a small envelope.