• Question: What's the Chance Earth Will Get Hit by a large Asteroid?

    Asked by sodiumpolyacrylate to David, James, Mike, Suze, Will on 18 Jun 2011.
    • Photo: Suze Kundu

      Suze Kundu answered on 18 Jun 2011:


      I’ve recently been looking into this. The robability changes, depending the size of the meteor potentially hitting Earth. Here is a link to a table that shows you the probabilities depending on the size:


      Interestingly, we are well overdue a ‘big’ impact. Our next possibility of impact will be in 2036, from a meteor called Apophis. Scientists thought that it might hit in 2029, but it’s going to pass Earth really close. There’s a chance that it might pass through this tiny patch of weirdness in space called a gravitational keyhole, which could potentially alter its future path so that it is definitely headed for is in 2036! I guess we’ll find out nearer the time!

    • Photo: William Eborall

      William Eborall answered on 20 Jun 2011:

      Can I add one statistical bit to that answer? We can’t really say “overdue” in this situation. I don’t know the numbers but lets say that every 10,000 years for the last 40,000 years a big meteor has hit that Earth, and the last one to hit did so 10,100 years ago. This might look like we’re 100 years overdue for an impact, but the meteor does know this. All we can say is that statistically the Earth is hit every 10,000 years and it’s been 10,100 years.

      Anyway I’m not worried as long as Bruce Willis is still alive 😉

    • Photo: James Marrow

      James Marrow answered on 20 Jun 2011:

      Just to emphasise the point correctly made by Will. It’s a common misunderstanding about probabilities. People often assume that a probability of “one in a thousand years” means that the event happens about once every thousand years. This doesn’t happen unless there is something that controls the events with a cycle (regular or repeating). Comets are a good example of this – they do move with a cycle, as does the moon and the sun. Some climate changes are also cyclic, as are some things that happen in the sun. There are small variations in these cycles, so events don’t happen like clockwork, but they are quite predictable. Other things are not cyclic (so far as we know), such as earthquakes or winning the lottery (so there’s no point watching to see how many times the number 27 comes up!), and these are not predictable from previous observations.