From Michael Paine
It is interesting to read about possible asteroids in other solar systems (12 August, p 15). I wonder if those asteroids hit rocky planets as often as such bodies hit Earth, say every 100 million years for an impact the size of Chicxulub, thought to have wiped out the dinosaurs. With some 30 billion rocky planets in our galaxy, that would mean one giant impact every day. A sobering thought for the chances of advanced life.
Beacon Hill, New South Wales, Australia
