In v5.70 there is an SM option to disable all sensors in a particular system. It is located on the Sensors tab of the system map sidebar. Once activated, there will be no detection phase for ships and planets in that system until it is turned back on again. The reason for this function is because one of the downsides of a multi-system Earth start is the number of detection checks grows exponentionally as you add extra races. If you happen to be playing a game in which you want to start multiple races on Earth but there will be a period without the likelihood of combat, you may want to disable sensor checks in Sol for a while for performance reasons. I think this option will be used rarely but it will be very useful in a few specific situations.
Steve