From time to time we see a headline like The end of the world IS nigh: Huge asteroid 'will hit earth in 2032' claim astronomers or a more modest one from this week's close-shave, Asteroid to hurtle past the Earth at 27,000 mph, and you are reminded of the random dangers that exist for us fragile creatures on this planet. I do have to grin whenever I hear the term "end of the world" (not used in the second article), because the end of the world will pretty much only happen when our Sun possibly consumes it in 5 billion years - the world is a big rock and hard to get rid of. What is intended in such phrases, of course, is the end of our lives on this world, which will happen at some point almost certainly much much sooner than that.
Whenever I see headlines about rocks flying close by, I go over to the Near Earth Objects site and look at the close approaches. This week's particular rock, labeled 2000 EM26, will pass within 9 lunar distances which is pretty close on the solar system scale.
It is educational, and fun, to read about these sorts of dangers. From the chart below, this week's rock, if it were to strike, would deliver well over 100 megatons of TNT of energy, much larger than our largest nuclear bombs. Yikes! Luckily, this is unlikely to happen - for this rock. However, it is likely to happen at some point. I'm not sure if that makes for an optimistic or pessimistic message, but I'll let you decide.