We transform sound into light, and the speed of light is 186,000 miles a second. So you divide the distance to Mars by the speed of light and you get the length of time it takes our light waves to reach Mars. Double that and you get the time it takes our messages to come back. Now, that could all be mechanical, but they don't come back in that exact number of minutes. It never takes less time, always more. Twenty seconds, forty seconds, sometimes as much as a minute and a half.