Torino 2, and Counting
Whether or not we acknowledge it, the possibility of an asteroid impact on the Earth continues to loom over us, along with the possibility that humankind may well go the way of the dinosaurs. Asteroid impacts may be rare, but they can have utterly devastating results; moreover, thinking about how to estimate and respond to asteroid impacts good practice for all kinds of thinking about big-picture, slow-changing planetary challenges. We now have another chance to practice.
According to New Scientist, asteroid 2004 VD17 has been given a Torino scale rating of 2 -- higher than any other object in the sky, at present -- indicating a small but measurable risk of impact. As of measurements on February 26, the asteroid has a 1 in 1600 chance of hitting the Earth in 2102 -- an increase over the initial estimate. So far, almost every time astronomers have discovered an asteroid on a potential impact course, subsequent refinements of the data confirm that the rock will miss us. It's extraordinarily rare for further refinement to increase the measured risk; the last time this happened was with asteroid 2004 MN4, which is now estimated to miss the Earth by a whisker in 2029.
It's likely that further observations will put the risk of impact at 0 -- but it's not guaranteed. Eventually, we will find that an asteroid is on a direct impact orbit, and we'll have to start thinking about how to deal with it. That's why this bit from the New Scientist article so frustrating: