The AAPG EXPLORER has been following the progress of the Perseverance rover and the history of the search for life on Mars. Perseverance’s journey in space culminated in its safe landing in Jezero Crater near Mars’ equator on Feb. 18, 2021. Now, Perseverance begins its journey of geologic exploration, fieldwork and the search for signs of past Martian life.
NASA and the Jet Propulsion Laboratory have deployed a series of successful and ever-more-sophisticated rovers. They have been deployed across the planet at carefully selected landing sites to explore for signs of Mars’ warmer and wetter past when it may have hosted the evolution of life. In Mars’ Noachian period, between about 4.1 and 3.7 billion years ago, the planet experienced extensive erosion by volumes of liquid water producing huge river valley networks. Large lakes and oceans were present. It is thought that the flood of water welled forth from the volcanic region known as the Tharsis Bulge. The great deluge raged down Valles Marineris rift valley, a canyon five times as long and deep as Earth’s Grand Canyon.
Sojourner: The Little Rover That Could
In April 1994, JPL Pathfinder project scientist Matt Golombek led the team for the selection of the landing site for the Pathfinder Mission and the first Mars rover, Sojourner. Viking orbiter images were studied, finding an area analogous to the channeled scabland in Washington state. This suggests that Ares Valles formed when hundreds of cubic kilometers of water was catastrophically released from a breached reservoir. Pathfinder landed on July 4, 1997 in the Xanthe Terra floodplain of the Ares Valles outflow channel. The rover used parachutes, retrorockets and finally an unconventional bouncing airbag for landing.
With a 20-minute light delay for communication, the rovers cannot be operated in real time. The Sojourner rover demonstrated that a rover could make some autonomous decisions to execute commands sent from operators on Earth.
The Pathfinder images showed rounded pebbles, cobbles and boulders similar to those deposited by catastrophic floods on Earth. The “Rock Garden” southwest of the lander has rocks that are inclined and stacked by ancient floodwaters. Sojourner demonstrated rock-analysis capability with its Alpha Proton X-ray Spectrometer, or APXS. A rock dubbed “Barnacle Bill” returned a composition consistent with typical basalt, similar to Mars meteorites that have landed on Earth.
The mission was planned to last about a month, but the rover operated successfully for almost three months and but traveled about 100 meters in the rugged terrain. The mission returned 16,500 pictures and made millions of measurements of Mars’ atmospheric pressure, temperature and wind speed. Eventually, the little rover succumbed to battery failure.
The Indefatigable Twin Rovers — Spirit and Opportunity
The Spirit and Opportunity rovers scaled up from Sojourner to more sophisticated, golf-cart-sized geology science labs called Mars Exploration Rovers. Each generation of Mars rover has developed a higher degree of autonomy to navigate and execute commands. The twin MER rovers were planned to operate for 90 Mars days but far exceeded expectations.
Nathalie Cabrol was the energetic spokesperson for the selection of Gusev Crater as the landing location of NASA’s Spirit rover on Mars. Steve Squyres of Cornell was the principal investigator for the MER missions. The rovers landed safely on airbags near the equator on opposite sides of Mars in January 2004. Their missions were designed to study the history of climate and past water processes at sites on Mars where conditions might once have been favorable to life.
Gusev Crater is interpreted to be an ancient dry lakebed. Again, the rocks on the plains of Gusev Crater are basalt. Spirit climbed from the plains onto Colombia Hills where rocks show various degrees of alteration due to water and brines depositing phosphorus, sulfur, chlorine and bromine, as revealed by APXS measurements. Additionally, the rover’s Mossbauer spectrometer found goethite, hydrated iron oxide, confirming the site’s watery past.
Spirit operated for six years and traversed 7.7 kilometers. Eventually, a wheel froze, dragging over the surface until Spirit became stuck and unable to recharge its batteries. Last contact was March 22, 2010.
The selected landing site for the Opportunity rover was Meridiani Planum. This is a large area determined to be rich in hematite from Mars Global Surveyor spectrometer measurements. Hematite also implies a past wet environment. Opportunity made a hole-in-one landing, bouncing and rolling on its airbags into the 70-foot-wide Eagle Crater in January 2004. This ideal location exposed Mars stratigraphy for Opportunity to begin to explore around the crater’s rim. Hematite was found nearly everywhere in small, round concretions dubbed “blueberries.”
The Martian aeolian, fluvial, and lacustrine sediments seem so familiar to geologists on Earth, many have said “I’ve walked that outcrop!”
The NASA Opportunity rover discovered the mineral jarosite on Mars in 2004, when it drove over fine-grained layers of it. This is significant since jarosite needs water to form. It also requires acidic conditions with iron, sulfate and potassium. Jarosite could indicate an ancient acidic lake or acidic hot springs.
In 2011, Opportunity found more evidence of Mars’ watery past on the rim of Endeavor Crater. Opportunity identified a thin layer of white gypsum, deposited perhaps in a transient lake billions of years ago. In December 2012, still in Endeavour Crater, Opportunity identified clay minerals that would have been deposited in a pH-neutral lake environment more suitable for life. Opportunity principal investigator Steve Squyres, declared, “Liquid water once flowed through these rocks. It changed their texture, and it changed their chemistry. We’ve been able to read the telltale clues the water left behind, giving us confidence in that conclusion.”
Like its twin, Spirit, the Opportunity rover was designed to operate for 90 sols (Martian days). The rover’s solar panels are the only means of keeping batteries charged. Both rovers suffered from dust accumulation, reducing the solar panels’ output. Fortuitously, passing dust devils occasionally served to clean the panels. Then in early June 2018, a planet-wide dust storm arose and choked out the sun. Opportunity could no longer charge its batteries. Last contact was June 10, 2018. Opportunity was declared lost after 1,000 attempts were made to restore communication. Hundreds of mission scientists and engineers said bittersweet goodbyes to one of NASA’s most successful missions. Opportunity operated for 14 years and traveled 45 kilometers.
Curiosity Rover: Mars Science Laboratory Still Going Strong at Gale Crater
Geologist John Grotzinger of MIT is the principal investigator of NASA’s Mars Curiosity rover. Curiosity has been operating successfully in Gale Crater since August 2012. It was a significant upgrade of Mars science rovers. It grew from golf cart-size to mini cooper car-sized – much too large to land on an airbag. Curiosity, and its successor Perseverance, also upgraded from dependence on solar panels to a radioisotope thermoelectric generator (RTG) power source using plutonium fuel. This provides the electricity the big rovers need to explore, run analyses and communicate with Earth.
Curiosity paved the way for the sky crane landing system that was also just used successfully for the even larger Perseverance. Adam Steltzner, the lead “rock and roll engineer” of Curiosity’s EDL phase (entry, descent and landing), helped design, build and test the sky crane landing system. When Steltzner explained the plan to NASA administrator Mike Griffin, he replied, “It might just be the right kind of crazy.”
Steltzner celebrated the “beautiful, sweet success” of the landing.
Mars scientists from around the world had a list of a hundred possible landing sites for Curiosity. They used detailed imagery and ultimately chose Gale Crater as the landing site with abundant indicators that water filled the crater repeatedly over its geologic history. Life as we know it requires water. Remote sensing shows sulfate minerals and clays in Gale Crater, having formed in the presence of water. The landing site gives Curiosity an access route to study the sedimentary layers of the central Mount Sharp inside Gale Crater. Scientists interpret that the crater was filled in with sediments. Over billions of years, Martian wind excavated Mount Sharp, which today rises about 3.4 miles above the floor of Gale Crater. Other interpretations suggest that Mount Sharp’s stature was accentuated by slow mantle rebound.
Ancient Lake Environment — Suitable for Life
One of Curiosity’s early findings was a fluvial braided stream deposit of rounded pebbles. Curiosity’s science instruments found that Mars once had the chemistry and environment to support living microbes. At Yellowknife Bay, the drill sample and lab instruments found life ingredients carbon, nitrogen, oxygen, sulphur and phosphorus. The analysis of clay minerals there implies a past freshwater environment.
When Curiosity reached Mount Sharp in 2014, the images and analyses revealed over 1,000 vertical feet of sediment and mudstone at Pahrump Hills. The sediments were deposited in a series of shallow lakes and rivers. This environment dominated Gale Crater for millions of years.
Organic Molecules and Methane
The sample analysis at Mars (SAM) instrument found organic molecules in drill samples from Mount Sharp and surrounding lowlands. Organic molecules are the building blocks of life. This finding is not proof of life on Mars, but the ingredients were there to possibly give life a start.
Methane was detected in the local atmosphere by the Curiosity’s tunable laser spectrometer in the SAM instrument. The methane levels in Gale Crater varied seasonally and peaked with a tenfold increase in methane over a two-month period in the Martian summer. Methane can be produced by living organisms in the subsurface or by mineral reactions with water and carbon dioxide. Perhaps the science instruments on the new Perseverance rover can unravel the mystery of Mars methane.
Curiosity was designed to last two years on Mars. It has been exploring for eight years and traversed 24.4 kilometers to date. It has more than 40 kilometers to go to summit Mount Sharp.
The Rover Drivers: What Time Is It on Mars?
Since the Pathfinder Mission, a special breed of engineers and scientists, proud to call themselves rover drivers, live on Earth but work on Mars. For the Mars 2020 Perseverance mission, Nagin Cox serves as the deputy team chief of the JPL Engineering Operations Team for the Perseverance Rover. She also worked on operations for Spirit, Opportunity and Curiosity rovers. Operations involve planning geology tasks and routes and then uploading instructions to the rover to execute.
Nagin and other rover drivers work on Mars time, with a day, or “sol,” being 24 hours and 40 minutes. Their sleep schedule adds the equivalent of a time zone every day, putting them a whole day out every three weeks. They still have to sort out Earth time versus Mars time.
“For those of us living on Mars time, we call ourselves Martians,” she said.
Since mission time on Mars is counted in sols, “Yesterday on Mars is ‘yestersol,’ tomorrow is ‘nextersol,’ and today is ‘tosol,’” she explained.
“Planners rely on 3-D images from Mars, usually studied through special goggles that rapidly shift between left- and right-eye views to better reveal the contours of the landscape,” Cox said.
Some tasks require testing with the rover’s twin on the Mars testbed at JPL. The down-to-Earth robotic Perseverance twin is called Optimism.
Nagin Cox and her operations team of rover drivers are stretching their legs on Mars with their new Perseverance rover. During the COVID-19 pandemic, using video conferencing to coordinate, the Curiosity and Perseverance rover teams work from the comfort of home to plan commands before sending them to Mars.
With Perseverance safely down and operating in Jezero Crater, mission geologists including JPL Deputy Project Scientist Katie Stack and Kirsten Siebach of the Perseverance Science and Operations Team, can begin exploration. We look forward to reporting on Perseverance’s geologic discoveries from our newest robotic explorer nextersol!