After two failed Mars missions in 1999, NASA's Jet Propulsion Laboratory (JPL) needed a hit, and they found it in Spirit. Spirit, a 384 pound rover, landed successfully on Mars on January 3, 2004. While scientists designed Spirit to only operate for 3 months and cover a kilometer of land, it ended up exploring Mars for over five years and traveled over 4.8 miles of land. Spirit even continued its explorations after suffering a broken wheel in 2006.
A few years later, Spirit suffered a second wheel breakdown when it became stuck in sandy soil. By January of 2010, scientists had given up hope of freeing Spirit, which transmitted its last message on March 22, 2010 when it went into hibernation for its fourth Martian winter. After unsuccessfully trying to revive Spirit with over 1,200 commands, scientists gave their last command early Wednesday morning on May 25, 2011.
Over the years, Spirit has sent over 124,000 images and made significant geological discoveries. We owe much of our current knowledge about Mars to Spirit. Here are some of the key findings:
- In 2004, Spirit exposed soil with relatively high levels of sulfur and magnesium sulfate, which could result from subsurface water.
- In late 2005, Spirit found high concentrations of carbonate in rocks, indicating that ancient Mars could have had a wet, non-acidic environment that was favorable for life. After four years of analysis, the findings were published in Science.
- In 2006 and 2007, Spirit studied a plateau called the "Home Plate", where it discovered evidence of an ancient volcanic explosion.
- From March 2007 to May of that year, Spirit dug up silica-rich deposits, as its broken front wheel dragged across the soil. The discovery provides evidence for a habitable environment in ancient Mars that had hydrothermal activity.
- After becoming stuck in sandy soil in early 2009, Spirit churned up subsurface soil layers that contain ferric sulfate during attempts to free itself. Combined with other evidence, the discovery indicates that ancient Mars may have had underground aquifers that fed seas.
Spirit's journey is over, but scientists are still learning from it. As its tire tracks fade, scientists can see how Martian winds and dust affect the planet's surface. Meanwhile, Opportunity, the other rover that landed on Mars in 2004, is still traversing across the surface with one broken wheel. Unquestionably, the two rovers are triumphant successes for NASA.