The Mars Exploration Rover Mission
Twin rovers Spirit and Opportunity launched from Cape Canaveral in 2003 and landed on opposite sides of Mars in January 2004. Their mission was to determine if early Mars had an environment that could have supported life. An aeroshell, backshell, parachute and retro rockets guided each rover through the martian atmosphere for an airbag-cushioned landing at two different locations along the red planet’s equatorial region. Using data obtained from orbiters, scientists had determined that these landing sites may have contained liquid water in ancient times. Spirit landed at Gusev Crater which was thought to be the site of a former lake, and Opportunity landed at Eagle Crater where data revealed the presence of the mineral hematite which usually forms in liquid water.
Each rover carried a suite of instruments called the Athena Science Payload to read the geologic record preserved in the rocks, soils and dust at the landing sites and beyond. This payload included a panoramic camera or Pancam to scan the martian terrain for rock and soil targets with two high-resolution color stereo cameras, a Miniature Thermal Emission Spectrometer called Mini-TES to see infrared radiation and identify minerals at target sites, an Alpha Particle X-Ray Spectrometer (APXS) to determine rock compositions, a Mössbauer Spectrometer (MB) to identify the composition of iron-bearing minerals, a Microscopic Imager (MI) for extreme close up views of rocks and soils, and a Rock Abrasion Tool (RAT) to brush and grind into rocks to reveal fresh surfaces for study. In addition, each rover carried three sets of magnets to collect dust for the instruments to examine. One set of magnets was located next to Pancam’s calibration target on each rover deck. The Pancam caltarget was also the first-ever interplanetary sundial.
The Spirit rover traveled from its landing location at Gusev crater across the plains to the Columbia Hills, studying a multitude of targets at West Spur, Husband Hill, Haskin Ridge, and Home Plate, a bright, almost circular plateau. Rock outcrops nicknamed “Comanche” contained magnesium iron carbonate. Carbonates originate in wet conditions with a near-neutral pH. Spirit also discovered deposits of a type of silica at Home Plate that almost always forms in hot springs or volcanic vents. These types of locations on Earth can harbor microbes called extremophiles. While studying the area around Home Plate, Spirit’s wheels broke through a crusty surface and became stuck in soft sand. It’s last transmission to Earth was on March 22, 2010.
The Opportunity rover traveled from Eagle Crater to Endurance Crater, Victora Crater, Santa Maria Crater, and Endeavour Crater. During the rover’s traverse, it found evidence of ancient acidic water as well as ancient water with a more neutral pH. Bluish pebbles nicknamed “blueberries” were found to contain the iron-based mineral hematite. On Earth, hematite usually indicates a history of water activity. Opportunity also discovered jarosite, another iron mineral that forms in acidic water. At Endeavour Crater, the rover found veins of gypsum, which is a sulfate mineral on Earth that can be left behind after water has evaporated. In addition, the rover discovered evidence of clay minerals that formed in ancient water with a more neutral pH, showing that at some point in Mars’ history there was a period more conducive to life (note: this was not evidence of life itself!). Opportunity’s mission ended in Perseverance Valley at Endeavour Crater when a planet-wide dust storm blocked the sun from providing energy to the solar arrays. A final communication was received on June 10, 2018.
The Mars Exploration Rover mission was designed to last 90 days, but Spirit continued to work on the surface of Mars for more than 6 years and Opportunity for almost 15 years. Like geologists who study the Earth, each rover used its suite of instruments and tools to look at its surroundings, study a rock target’s texture, size and color, crack it open to understand how it was formed, examine its mineral content, study the soil where the rock was found and monitor the dust that hangs in the air. Target by target, Spirit and Opportunity pieced together a picture of a very different Mars than we see today, one with a watery past that could have included microbial life.
LEARN MORE at the MER Analysts Notebook