When scientists wanted to explore what kind of life might exist on Mars, public television’s “NOVA” recorded the building and launch of the rovers sent to the planet. Now, a year later, the “NOVA” team is back with “Welcome to Mars,” featuring data collected by the robots as they searched for signs that the planet may once have harbored tiny forms of life. The program airs Tuesday at 8 p.m. EST on PBS (check local listings).