Search for life on Mars and disappointment
The Mars Reconnaissance Rover (MER) project, which brought the twin rovers Spirit and Opportunity to life, received approval in 2000 with a target readiness date set for 2003. The window for launch opened when Mars and Earth aligned in a favorable orbit, allowing a heavier payload to ride a mid-range Delta II rocket. Typically missions like this demand more than three years of development, but the decision to launch came swiftly, spurred by an unexpected opportunity.
As the century closed, public excitement for Mars waned. In the 1960s, scientists wondered aloud about life on Mars. The arms race between the USSR and the United States framed the era, with the Soviet Mars-3 probe failing after a brief signal. Viking 1, launched by the United States, became the first successful lander, followed by Viking 2. Those missions raised fears about what orbiting images might reveal, confirming a harsh reality.
Mars proved to be a cold, barren desert. If life did exist, any organisms would likely be microbe-sized and deeply buried.
Frustration set in as Mars missions stalled for nearly two decades after a string of setbacks, including Russia’s Mars 96 failure caused by a rocket mishap. The Viking program consumed about a billion dollars in 1970s dollars, a sizable investment that today would translate to several major missions and platforms.
In response, space planners pivoted to cost-conscious missions, pioneering compact rovers like Sojourner. That small craft yielded the Yogi Stone, a rock carved by ancient water flow, providing early, tangible evidence that Mars once hosted watery conditions. NASA then approved the MER project about three years after those photographs emerged, assigning development to the Jet Propulsion Laboratory.
two twins
Building a complex rover from scratch within three years isn’t feasible, so engineers reused many components from prior missions. They borrowed the Sojourner landing system, which had demonstrated soft landings on other bodies. Traditional landings relied on rocket engines to achieve a gentle touchdown. If a lunar rover was aboard, it would sit on the landing platform and slide down a ramp. These systems demand extraordinary reliability since automation must choose engine pulses precisely based on altitude, velocity, and remaining fuel.
Earlier lunar and Martian attempts exposed several failures. In 1999, the American Mars Polar Lander crash underscored how electronics timing could go wrong. Ground-contact sensors activated at too high an altitude, triggering an abrupt engine shutdown. Even with flawless systems, a platform can topple if a leg strikes a rock or a crater is encountered. A rocket-powered lander is heavy, so payload deployment can become a more efficient option.
Thus MER relied on inflatable pads that mimicked enlarged Sojourner pads. After detaching from the transfer module, the lander entered the Martian atmosphere, with the heat shield absorbing the initial impact and easing descent. A parachute slowed the craft to a safer speed, followed by the removal of protective layers and the descent of a pyramid-like housing containing the rover.
At a certain altitude, six large inflation cushions expanded on each side. On Earth, this design could cushion a drop from a high floor, but Mars gravity is only about a third of Earth’s. Descent rockets mounted on the capsule then reduced speed to near zero. Between 20 and 50 meters above the surface, cables released, and the pyramid and rover separated. The platform bounced several times as the inflated structure absorbed the shocks. The descent lasted roughly six minutes.
When sensors confirmed the landing sequence was complete, the pyramid opened. If the platform landed upside down, folding wings could reorient it. During descent, the rover folded its wheels, mast, solar panels, and antennas. Once the platform deployed, the rover powered up and began drawing power from its solar arrays.
Martian centenarians
Spirit landed on January 4, 2004, in the equatorial region near the Gusev crater, where orbital imagery had already indicated signs of past water. Opportunity followed on January 10, touching down at Eagle Crater on the planet’s opposite side. A nominal 90-day mission began with high scientific expectations.
The Mars rover design drew on previously developed ideas from JPL. Spirit and Opportunity weighed about 185 kilograms and measured roughly 1.6 by 2.3 by 1.5 meters. Notable features included mast-mounted navigation cameras, solar panels, and a robotic arm that resembled folded wings.
The robotic arm carried four primary instruments borrowed from the canceled Mars Surveyor 2001 mission: a microscope with a digital camera to study mineral structures, a Mössbauer gamma spectrometer for iron-bearing rock composition, an X-ray alpha particle spectrometer to analyze soil chemistry, and a stone abrasion tool to clean dust from rocks. A magnetic grid captured magnetic dust for study.
MER missions far exceeded their expected lifespans: Spirit operated for 2695 days, while Opportunity kept communication for 5498 days, last contacting Earth in 2018.
The rovers endured a harsh beginning: Spirit faced a freezing winter, and Opportunity’s solar arrays collected a thick dust layer. Although they did not make certain breakthroughs like later rovers Curiosity and InSight, they yielded a wealth of knowledge about Mars’s past. Opportunity found hematite, a mineral tied to ancient water, and Spirit revealed rocks rich in magnesium and iron carbonates. The team confirmed extensive silica formations, commonly linked to hot springs on Earth, which fed clues about a habitable past.
Disappointment lingered over the lack of clear evidence for an ancient Martian lake in Gusev crater, where deep clastic deposits suggested a more complex history. Looking ahead, newer missions such as Curiosity (2012) and Perseverance (2020) would pursue more definitive evidence of ancient water networks. Perseverance continues to collect samples for a future return to Earth, a mission that could unlock further secrets about Mars’s long and dynamic history.