REMS Twins is the nickname given to the two identical spacecraft, Opportunity and Spirit, that were part of the Mars Exploration Rover (MER) mission managed by NASA’s Jet Propulsion Laboratory. The rovers landed on Mars in January 2004 and conducted surface operations until 2010 and 2011 respectively. The twin rovers have made important discoveries about the history of water on Mars and unlocked mysteries of the red planet’s past environments.
Quick Answers
The formal names of the two Mars rovers are:
- Mars Exploration Rover A (MER-A) – Opportunity
- Mars Exploration Rover B (MER-B) – Spirit
Their nicknames are derived from the acronym REM which stands for Rover Environmental Monitoring Station. Since there were two identical rovers, they became known as the REM twins or REMS twins.
Mission Overview
The Mars Exploration Rover mission was launched by NASA in 2003 with the goal of searching for evidence of past water activity on Mars. The mission consisted of two rovers which were identical in design and instrumentation. They were launched separately in June and July 2003 and landed at two different locations on Mars in January 2004 – Opportunity landed in Meridiani Planum and Spirit landed in Gusev crater.
The two sites were selected for their ancient geological conditions that might have been favorable for past water activity. The prime mission was planned to last 90 sols (Martian days) but both rovers continued to explore Mars long past their expected lifetimes. Opportunity operated on the surface of Mars for nearly 15 years while Spirit lasted 6 years.
Opportunity Rover
The Mars Exploration Rover A was named Opportunity. It landed at Meridiani Planum on January 25, 2004. Meridiani Planum was chosen as a landing site because orbiter observations hinted at deposits of the mineral hematite which typically forms in presence of water. During its explorations, Opportunity discovered evidence that parts of Meridiani Planum were once soaked in liquid water in the past.
Some key findings from Opportunity’s mission include:
- Discovering laminated bedrock containing hematite and gypsum – minerals that precipitate out of water
- Finding small spherical concretions nicknamed “blueberries” that are made of hematite
- Uncovering evidence that Meridiani Planum used to have mildly acidic groundwater
- Identifying impact rocks that provide clues about Mars’ ancient environment
In its 15 years of surface operations, Opportunity traversed over 45 km and found definitive evidence that ancient Mars was wet and may have been habitable for microbial life.
Spirit Rover
The Mars Exploration Rover B was named Spirit. It landed at the Gusev crater on January 4, 2004. Gusev crater was thought to be an ancient lake bed, so a prime target in the search for evidence of past water activity. During its explorations, Spirit uncovered deposits that were formed in the presence of water.
Some key findings from Spirit’s mission include:
- Discovering high concentrations of silica that likely formed in hot spring environments
- Evidence that the region may have hosted a hydrothermal system
- Uncovering deposits of nearly pure carbonate that precipitates from water
- Confirming that Gusev crater once held a lake that could have been habitable
Before it ceased communications in 2010, Spirit traveled over 7.7 km on the Martian surface, overcoming many challenges from dust storms and mechanical failures.
Rover Design and Capabilities
The Mars Exploration Rovers were designed to be robust, mobile robot geologists. They are about 1.6 m long, 2.3 m wide and 1.5 m tall, with a mass of 180 kg. Some key design elements and instruments:
- Six aluminum wheels with cleats for climbing rocks
- Solar arrays generate about 140 Watts of power
- Capable of traveling up to 50 mm per minute
- Pancam – Panoramic camera provides color images
- Navigation cameras used for navigation
- Miniature Thermal Emission Spectrometer (Mini-TES) identified minerals
- Mössbauer spectrometer analyzed mineral composition
- Rock Abrasion Tool (RAT) brushed and ground rock surfaces
This suite of mobility and science instruments allowed the rovers to analyze geological textures and chemistry to uncover clues about Mars’ watery past. Being mobile platforms greatly expanded the area the rovers could explore compared to stationary landers.
Key Engineering Innovations
The Mars Exploration Rovers implemented several innovative engineering solutions that enabled them to last over 5 years on Mars – far exceeding their original 90 day mission timeline. Some key innovations were:
- Rover designs optimized for survival: Low center of gravity, rocker-bogie suspension system and aluminum wheels optimized for driving on rough Martian terrain.
- Heat rejection systems: The rovers were designed to survive the frigid Martian nights where temperatures drop to -120°C. They used radioisotope heater units and layered insulation to maintain operating temperatures.
- Power storage: Lithium ion batteries powered nighttime operations and allowed the rovers to survive dust storms that blocked sunlight.
- Robust flight software: The rovers were able to detect and autonomously recover from problems with motors, sensors and software.
Thanks to these innovations, Spirit and Opportunity greatly exceeded expectations and collected enormous amounts of data about Mars during their extended missions.
Top Discoveries
During their many years exploring the Martian surface, the Mars Exploration Rovers made several groundbreaking discoveries that reshaped our understanding of Mars. Some of the top findings include:
Evidence of Past Surface Water
Both Spirit and Opportunity found multiple lines of evidence showing that Mars was once much wetter than today. This included mineral deposits, sedimentary layers and morphological features that could only have formed in the presence of liquid water.
Potentially Habitable Ancient Environments
Analyses of rock chemistry and mineralogy showed locations like Meridiani Planum and Gusev crater once had wet and mildly acidic environments billions of years ago that may have been potentially habitable for microbial life.
Diverse Ancient Martian Environments
The rovers uncovered evidence for diverse ancient wet environments including lakebeds, hot springs, explosive volcanism and deep groundwater.
Modern Water in Mars’ Atmosphere
Opportunity’s observations after a planet-wide dust storm confirmed that Martian air contains minute traces of water vapor today.
Meteorite Impacts Shaped Mars’ History
Analyses of impact rocks and craters showed that meteorite impacts played an important role in Mars’ geological history and may have generated transient habitable environments.
These discoveries provided pivotal evidence that Mars was once an active and wet world, setting the stage for future robotic and human exploration of the red planet.
Longevity and Scientific Impact
The Mars Exploration Rovers generated immense scientific returns for many years beyond their design lifetimes. Some key metrics include:
- Opportunity operated for 14.6 years and traveled 45.16 km
- Spirit operated for 6.2 years and traveled 7.73 km
- Over 340,000 images were transmitted
- 215 gigabits of data was returned
- Hundreds of scientific papers were published based on rover data
The long-lived rovers enabled Mars scientists to conduct detailed long-term studies of Martian geology and atmospheric science. Spirit and Opportunity returned such a wealth of high quality data that they laid the foundation for all subsequent Mars exploration missions.
Extended Missions
After completing their 90 day prime missions, both rovers were approved for multiple extended missions. These extended missions allowed them to explore new sites and make additional discoveries.
Enabling Future Missions
The rovers served as pathfinders for future surface missions by validating concepts like airbag landings and demonstrating long-term survival on Mars. They provided ground-truth observations for orbiters. The rovers generated detailed maps that were used to plan future rover traverses for Curiosity and Perseverance.
Public Engagement
The adventures of Spirit and Opportunity engaged the public like no other Mars mission. People around the world followed along as the rovers explored the alien landscapes of Mars. Schoolchildren participated by suggesting rover targets. The long lived rovers became global pop culture icons.
End of Mission
After many years atop Mars, both rovers eventually succumbed to the harsh Martian environment.
Spirit
Spirit’s final communication was received on March 22, 2010 after getting stuck in soft soil the previous year without enough power to survive winter. Spirit’s groundbreaking achievements ensured it went down fighting after 12 times its planned lifetime.
Opportunity
Opportunity exceeded all expectations by exploring Mars for over 14 years. A planet encircling dust storm blocked sunlight in 2018 leading to a low power condition. NASA officially ended the mission on February 13, 2019 after failed recovery efforts. Opportunity set rover records for longevity, distance traveled and scientific discoveries.
Legacy
The Mars Exploration Rovers left an immense legacy from their tremendously successful missions. Some aspects of their lasting legacy include:
- Dramatically increased our understanding of Mars’ past environments and habitability.
- Found definitive evidence that Mars was once wet and could have supported life.
- Uncovered clues about how Mars transformed into the cold dry world we see today.
- Returned a wealth of high quality data that will be analyzed for decades.
- Pioneered technological innovations in Martian mobility and autonomy.
- Inspired generations to pursue careers in STEM fields.
- Laid the groundwork for future Mars exploration by rovers and humans.
Spirit and Opportunity accomplished all their major goals and far exceeded expectations. Their discoveries and technological demonstrations will be an enduring legacy in the history of Mars exploration.
Conclusion
The Mars Exploration Rovers – Spirit and Opportunity – completed pioneering missions to uncover evidence of Mars’ watery past. These identical robotic geologists found numerous signs of ancient wet environments that may have supported life. The groundbreaking rover missions captivated the public while their scientific discoveries forever altered our view of the red planet. Although their journeys have ended, the achievements of Spirit and Opportunity will live on as an inspiration for future exploration of Mars.