The pair of rovers landed on opposite sides of Mars in 2004, carrying identical payloads of instruments, including panoramic cameras and spectrometers for examining soil. Their original assignment, to explore local rocks for signs of past water, was meant to last just three months. Although Spirit is now out of commission, Opportunity is still going strong.
Bonus science: Spirit was able to trek to a nearby group of hills to collect extra data. Opportunity is currently exploring clay-bearing rocks in Mars’ Marathon Valley for evidence of minerals that formed in water.
Why it’s still on the job: Martian winds clean dust from the rover’s solar panels.
Achilles’ heel: Though the rovers were designed to handle the Martian sand, Spirit shut down in 2011. Its
wheels outlived their designed
life span, and some of them stopped working. This caused Spirit to get stuck in the sand in 2009. No longer mobile, it couldn’t turn its panels toward the sun to recharge and was unprotected against winter temperatures of minus 67 degrees Fahrenheit. NASA heard Spirit’s last few beeps in 2010, and in 2011 was unable to make contact with it again.
Mars Reconnaissance Orbiter