2004

Spirit and Opportunity on Mars

More than three decades of successful orbital and landed investigations of Mars by scientists involved in the Mariner and Viking missions painted a compelling picture of major past climate changes on the Red Planet. The Martian surface today is extremely cold, bone dry, and inhospitable to life as we know it. But ancient Mars, as revealed by these missions, appears to have been a warmer, wetter, and potentially more Earthlike place. If so, then early Mars (during the first billion years or so after its formation) may have been a habitable environment where, as on our own planet, life could have thrived.

Planetary scientists wanted to move beyond photographic evidence of a potentially habitable early Mars, however, and make quantitative geologic, geochemical, and mineralogic measurements that could provide smoking-gun proof. Experience gained from the 1997 Mars Pathfinder mission proved the value of mobility in doing geologic field work with robots in distant locations, leading to the choice to embark on an even longer-range rover mission. Because of two Mars missions failures in 1999, NASA decided to reduce its risk: instead of just one rover, it would launch twin rovers—named Spirit and Opportunity—in 2003.

Both rovers landed safely in early 2004 and began their separate adventures on opposite sides of the planet: Spirit in an ancient crater named Gusev, which may once have hosted a lake, and Opportunity in the cratered area Meridiani Planum, where Mars Global Surveyor data showed evidence for water-formed minerals. After several years of virtually roving around Gusev with Spirit, mission scientists discovered evidence of water-bearing minerals in an ancient hydrothermal system that provided smoking-gun evidence for past habitability in Gusev. At Meridiani, the team immediately found other water-formed minerals like hematite, clays, and sulfates that provided smoking-gun evidence for past habitability there as well. Despite their expected lifetimes of just ninety days, Spirit operated until early 2010, and as of mid-2018 Opportunity continues to roll on and make new discoveries.

A computer-generated version of the NASA Mars rover Opportunity placed into an actual Opportunity Pancam mosaic of finely layered rocks inside Endurance crater. These rocks contain evidence of past liquid water on Mars, including millimeter-size iron-rich spheres (inset) called concretions.