A hard planet to reach. Mars has been a tempting goal for NASA and other space agencies since the early 1960s. Yet of the 42 missions launched toward Earth’s neighbor, fewer than half reached their objective and returned significant data. The plot shows the results for each decade. The 2000s saw the most success. Of its six missions, all survived longer than expected and four — Mars Express, Mars Odyssey, Mars Reconnaissance Orbiter, and Opportunity — continue to function.