The Editor,

New Scientist

Dear Sir

The article on the Mars Rover, in the Xmas issue, misses the obvious explanation as to why the Martian dust has miraculously disappeared from the solar panels of the vehicle. "Squeegee kids" appeared spontaneously in many North American cities around 5 years ago. These young people would rush up while you were stopped at a traffic light , smear dirty water over the windscreen of your car and sullenly demand financial compensation.

Fortunately for Western civilization, their activities are now restricted by the "Safe Streets" Act in Ontario and the equivalent in other areas. Obviously this enlightened legal approach has not yet reached Mars, so that "these exciting and unexplained cleaning events have kept Opportunity in really great shape"

This not only explains a comparatively trivial short-term mystery, but a much more profound one: why has Mars' water disappeared? Obviously: too many squeegee kids.

But one remains: how is NASA going to tip the squeegee kids on Mars?

Peter Watson