Mars is not far away on a calendar. It is far away on a schedule — and the schedule only opens about once every 26 months. This month, you can watch it open. Every Mars mission you have ever heard of left Earth inside a narrow band of weeks. Not because launch providers like deadlines, but because the solar system imposes one. Earth circles the Sun in about 365 days; Mars takes about 687. The faster planet keeps lapping the slower one, and the two only line up in the geometry