Celebrating the Mars Exploration Rovers

mars exploration rover
The NASA Mars Exploration Rovers (MER) spacecraft were sent to explore the surface of Mars. They are called Spirit and Opportunity. NASA

Meet the Mars Exploration Rovers

What's the longest-running mission to explore the surface of Mars? As of January 2017, the Opportunity  Mars Exploration Rover (MER) has that honor. It, along with its twin rover Spirit, set out on what has turned out to be nearly a decade and a half of Mars studies. Opportunity is still working, while Spirit failed in 2010, after seven years of operation. It's worth noting that these rovers originally had planned 90-day missions, and they each far surpassed their goals.


These robot geologists were programmed to do what are called "in situ" studies of the rocks and atmosphere in selected spots on Mars. They landed on January 3rd and 24th, 2004, on opposite sides of Mars and immediately set to work studying their surroundings. Spirit landed at Gusev Crater and Opportunity settled down at Meridiani Planum. Gusev was once filled by a lake, while the Meridiani region shows evidence of once having liquid water.

Roving Goals on Mars

The goals of the MER mission are to search out rocks and soil that may have been in contact with water, and study their chemical makeup. Each rover is equipped with a panoramic camera (Pancam), a miniature thermal emission spectrometer (to identify rocks and soils chemically), a Mössbauer spectrometer (to study the mineral content of rocks on Mars, that is, to do spectroscopy on them), an alpha particle x-ray spectrometer to do close-up analysis of elements in Mars rocks and soil, magnets to collect magnetic dust particles for the spectrometers to study, a microscopic imager to provide up-close images of rocks and soils, and a rock abrasion tool (nicknamed the RAT) to clear off rocky surfaces so other instruments could study them.

The rovers can travel across the rocky and sandy Martian terrains at a top speed of two inches per second. In practice, they usually move more slowly. Both have solar arrays to provide power for the onboard batteries. Over time, those solar arrays became covered with dust. The Spirit rover, which was the first to image small dust storms called “dust devils”, also benefited from these little whirlwinds because they cleaned the dust off its solar panels as they passed overhead.

That allowed the solar panels to capture more sunlight to help charge up the batteries on the rover. 

Spirit’s Adventures

Spirit traversed across nearly five miles of Martian terrain before shutting down for good in 2010. That March, it likely entered a low-power hibernation state, and never woke up. Mission controllers suspect that its batteries were too low to keep the mission clock running.

Spirit is still perched at a spot called “Troy”. Its landing site was called Columbia Memorial Station, after the astronauts who died in the Columbia shuttle disaster. Its final resting spot is in the Columbia Hills, also named for the lost astronauts. 

Opportunity’s Adventures

The Mars Exploration Rover Opportunity mission continues to roll. Opportunity was also scheduled for 90 days, but has lasted well more than a decade, and has traveled more than 25 miles so far. It has visited Endurance Crater, Erebus Crater, and Victoria Crater, where it spent nearly a year exploring the rock ledges and sandy pit of the crater. Along the way, Opportunity has studied many different types of soils and rocks that came into contact with water in the past. The data it has gathered is allowing planetary scientists to determine the water history of the Red Planet in greater detail.

They know it was warmer and wetter in the past, but the devil is in the details about specific lakes, oceans, and rivers that existed on that ancient Martian terrain. The rover continues to explore the Martian surface around Endeavour Crater, measuring and analyzing rocks and sending back spectacular images of the surrounding landscapes. 

Each of the two Mars Exploration Rovers have sent back many panoramic and scientific images of the Mars surface, as well as close-up shots of rocks, including a meteorite. The images and data sets they provided will be of tremendous interest to scientists sending the next landers to Mars, as well as future Mars explorers when they land to study the Red Planet in person.