Last year, scientists proposed nearly 50 locations on Mars as possible places for future human landings. Those landing-zone sites contain "regions of interest" that can be reached from primary touchdown spots. Good touchdown sites will allow crews to land safely and carry out operations; offer a wealth of interesting science activities; and provide resources that the astronauts could use. For example, any favored exploration zone should allow expeditionary crews to tap into at least 100 metric tons (110 U.S. tons) of water, NASA officials have said. With its suite of instruments and cameras — particularly the sharp-shooting High Resolution Imaging...