A manned trip to Mars is a justified scientific goal because it affords a unique opportunity to explore the origins of the solar system and the emergence of life. However, from a scientific standpoint, an initial landing on the tiny Martian moons, Phobos and Deimos, would be more rewarding than a landing on the planet itself. Because the Martian terrain is rugged, humans would not be able to venture far, nor could they operate a robot vehicle for great distances, since Mars’s mountains would block their view. Explorers on Phobos and Deimos could easily send robot vehicles to the planet’s surface. Using Mars’s moons as a base would also be better than unmanned exploration directed from the Houston space center. Because the distance is so great, radio signals to and from Mars can take as long as an hour. Thus, driving an unmanned rover from Earth, step by step, would be a time-consuming operation. Sample returns to Earth would take months instead of hours, and follow-on missions would be years apart instead of days, further slowing the process of exploration.

The following arguments gradually increase in difficulty. Use the method presented in this section to construct argument patterns. If a statement is redundant or plays no role in the argument, do not include it in the pattern.