On June 10, 2003, NASA's Spirit rover embarked on its seven-month journey to Mars from Cape Canaveral, marking its 20th anniversary today. Launched a month prior to its twin, Opportunity, Spirit was part of the “Mars Exploration Rovers” initiative. At that point, only one rover, the small Sojourner, had successfully operated on Mars, having arrived in 1997 with the Pathfinder lander. This was shortly after NASA's Mars Global Surveyor spacecraft entered orbit. However, the 1990s and early 2000s were challenging for Martian exploration.

In 1993, NASA lost contact with the Mars Observer just three days before it was due to enter Martian orbit, likely due to a propulsion system failure. This was NASA's first attempt to return to Mars since the Viking missions of the 1970s, making the loss particularly disheartening. Russia's ambitious Mars 96 mission, which aimed to deliver two landers and two penetrators, also ended in failure when it crashed back to Earth. Japan's Nozomi mission, launched in July 1998, failed to achieve orbit due to fuel system malfunctions, ultimately ending up in a solar orbit. NASA's Mars Climate Orbiter and Mars Polar Lander, launched in late 1998, suffered infamous failures—one due to a metric-imperial unit conversion error and the other presumed to have crashed during landing. The European Space Agency's Beagle 2 mission in 2003 also failed to establish contact after being deployed from the Mars Express orbiter. Between 1990 and 2003, over half of the Mars missions launched by humans encountered some form of failure.

Given the setbacks with Mars Climate Orbiter and Mars Polar Lander, much hope rested on Spirit and Opportunity. NASA did successfully place the Mars Odyssey mission into orbit, which remains the longest-operating mission at Mars today. However, they had not returned to the surface since Pathfinder ceased operations in 1997.

As Spirit's landing approached, anxiety mounted among mission operators when no signals were received for the first few minutes. Engineers anxiously monitored their screens, hearing only, “no signal at the moment,” followed by “standby.” After a tense 15 minutes, the rover finally made contact, confirming its safe landing!

Fortunately, both Spirit and Opportunity exceeded their expected lifespans of 90 sols (Martian days), with Opportunity receiving the majority of the attention for its longevity and dramatic demise during a massive dust storm. Nonetheless, Spirit's contributions to our understanding of Mars during its 2,210 sols on the planet are invaluable. In honor of its launch anniversary, let's explore five significant scientific achievements of the Spirit rover:

1. It’s Getting Hot in Here

A few years into Spirit's mission, the rover's front right wheel malfunctioned. Ingeniously, engineers decided to drive the rover in reverse, allowing it to continue exploring while dragging the damaged wheel. After 1,150 sols, Spirit encountered softer ground that left a trench behind, revealing previously buried material. Upon analysis, scientists determined this material was silica, indicative of a past hydrothermal system with water heated by volcanic activity beneath the surface. On Earth, such systems are rich in life, raising intriguing possibilities about ancient microbial life on Mars 3.5 billion years ago.

2. Neutral Waters

Both Spirit and Opportunity uncovered various sites indicating past water presence. Spirit specifically identified the least acidic waters yet found on Mars at a site called Comanche, where spectral data revealed magnesium iron carbonate in the rocks. Carbonates are generally scarce on Mars, making this discovery particularly significant, suggesting that the water present when the carbonates formed had a neutral pH—conditions conducive to life.

3. An Explosive Past

Mars is home to numerous volcanoes, including Olympus Mons, the largest in the Solar System. These volcanoes exhibit Hawaiian volcanism, where lava flows gently. However, explosive eruptions can occur if hot lava interacts with water. This phenomenon was observed at a site named Home Plate, where Spirit captured an image of what scientists interpreted as a "bomb sag," suggesting that water was once present there, possibly leading to explosive volcanic activity.

4. Dust in the Wind

Mars experiences its own weather systems, including dust storms and dust devils. Spirit was the first mission to capture dust devils in motion, revealing that these small whirlwinds are common on the Martian surface. Dust devils play a beneficial role for solar-powered rovers by cleaning dust off their panels, providing them with much-needed energy.

5. Cracking the Crust

In May 2009, Spirit became stuck in deep sand, shifting its mission focus to stationary science. As it attempted to extricate itself, it broke through a crust, exposing material with the highest sulfate mineral concentrations observed on Mars. This finding reinforced the evidence for a past hydrothermal system, suggesting that warm water could have supported life in early Mars.

Saying Goodbye

Despite extensive efforts to free Spirit from the sand, the rover remained stuck as Martian winter set in, leading to dwindling power levels. Contact was lost on March 22, 2010, and after over a year of silence, NASA officially concluded the Spirit mission on May 24, 2011. Spirit outperformed its mission expectations, lasting nearly 25 times longer than planned and capturing over 124,000 images.

NASA initially considered landing its Perseverance rover at Spirit's last location to continue investigating the area's hydrothermal history and implications for ancient life. Ultimately, Jezero Crater was selected as the more scientifically promising site, though the curiosity about Spirit's current state and any undiscovered science it may harbor remains.

Perhaps one day we will uncover those secrets.

Note: Some may argue that the USSR's Mars 3 rover achieved brief functionality in 1971, but its signal lasted only 20 seconds and yielded no usable data, making it an unsuccessful mission in my view.