With July of this year, 2023, being the hottest on Earth yet recorded, there are increasing concerns about how climate change will shape the next several decades. We often hear about how climate change will increase disastrous weather events, decimate crops, and...
In February 2021, three missions arrived at Mars. China’s Tianwen-1 reached the red planet on February 10, one day after the United Arab Emirates’ Amal (Hope) went into orbit. Hot on their heels, NASA’s Perseverance rover arrived on February 18th and, independent of mission control, successfully descended to Jezero Crater.
This descent was dubbed the seven minutes of terror because it all took place before the signals reached Earth. First, it was slowed by Mars’ thin atmosphere, then by a supersonic parachute, and then it was finally lowered to the surface using a skycrane (the descent vehicle firing retrorockets to counter gravity and further slow and guide the rover) – all without any direct guidance from Earth. Perseverance is the 9th of the NASA Mars landers and, not surprisingly, it will be the most ambitious of the robotic explorers. It will collect and store rock and soil samples that will be returned to Earth for analysis on a later mission. About the size of a small car and weighing almost one ton, Perseverance carries twice the payload of the Curiosity rover.
In the early 70s, the Soviet Union was first out of the gate with missions to Mars that included soft landers, but all were these were failures. While two Soviet landers did reach the surface, neither survived the descent, with one crashing and the other being knocked over in fierce winds. Another failure was the British Beagle II, named after Darwin’s ship. It landed in 2003, but never sent any data, and later images from orbiters indicated that the Beagle’s solar panels never opened correctly. While NASA robots were not the first to reach the surface, they were the first to actually survive the landing.
Over time, landing maneuvers, instruments, and goals of NASA’s Mars rovers have evolved. With each new mission, some questions are answered, but others are raised. Below is a brief summary of successful Mars explorers, their objectives and some of their findings.
Viking 1 and 2
In 1976, Viking 1 and 2 landed on the Martian surface in 1976. Unlike later missions, they made their soft landing thanks to engines that slowed each of the landers and steered them to their landing sites. Besides taking photos and collecting measurements on the surface and atmosphere, they also performed biological experiments looking for signs of life. While most astrobiologists agree that these landers collected no clear evidence of Marian life, some of the data was inconclusive data. The landers survived for six years and three and a half years, respectively.
Pathfinder and Sojourner
On July 4, 1997, the Pathfinder/Sojourner mission successfully landed on Mars. Pathfinder was a stationary lander that served as a base for its companion, the small Sojourner rover, which was named after abolitionist and women’s rights activist Sojourner Truth. The microwave-sized rover had an earth-weight of 25 pounds and traveled 100 meters over the course of two and a half months, photographing Mars and analyzing soil and rock. But most importantly, it was the first test of a Martian rover. Science fiction fans might recall the Pathfinder and Sojourner from the film, The Martian.
The Polar Lander’s mission was to study the climate and soil near Mars’ South Pole. But in 1999, it crashed, most likely when its engine shut off to soon.
Spirit and Opportunity
June 2003 saw the landing of two rover explorers, NASA’s famed Spirit and Opportunity. After a seven-month journey, the rovers landed in January 2004, about three weeks apart. Spirit and Opportunity used a new landing technology: after being slowed by a parachute, they deployed a cluster of airbags that let them bounce along the surface. Landing on opposite sides of Mars, both long outlived their three month and 2000-foot expectations. Opportunity worked for 15 years (60 times its life expectancy) and traveling 28 miles; Spirit explored for six years, covering 4.8 miles. The twin rovers found a wealth of evidence that Mars was once much warmer and wetter. But was this sufficient for life?
In 2010, the Phoenix lander arrived near Mars’ North Pole. Traveling at 12,500 miles per hour, it was slowed near the surface by its heat shield, a parachute, and finally, engines that guided Phoenix to the surface. A stationary lander, Phoenix completed all of its experimental goals in three months before it stopped transmitting. Phoenix found water ice beneath the polar surface and provided further evidence that Mars was once a watery world.
In 2012, the Curiosity Rover touched down in Gale Crater, using the skycrane technique recently used with the Perseverance rover. The size of an SUV, it carried 17 cameras, a drill, and a laser to vaporize rocks. Knowing Mars’ watery past, Curiosity’s mission is to determine if Mars ever had a habitat that could support microbial life. Chemical and geological evidence seem to support this conjecture. Nearly 9 years after landing, Curiosity is still roving and returning data.
In 2018, Mars Insight, a stationary lander, reached the planet. While also monitoring weather and atmospheric changes, Insight’s main focus is to study the deep interior of Mars. Seismic activity already shows that Mars is more geologically active than previously thought. While it does not have tectonic plates, Mars does have quakes – less intense and less frequent than Earth – and volcanic activity beneath the crust. The lander is still operating after two years.
In a sense, 2021’s Perseverance Rover brings the Mars landers full circle. While the Viking mission’s search for life was inconclusive at best, the rovers that followed sought to show Mars could have once supported life. Along with collecting rocks for a return mission set for 2026, Perseverance is now seeking evidence that life once existed on Mars. And along with the usual array of complex tools, Curiosity carries a helicopter, named Ingenuity, that will be the first vehicle to fly on a body other than Earth. Later this summer, Perseverance will be joined by a rover now aboard Tianwen-1, perhaps giving earthlings four landers working simultaneously, plumbing the secrets of the red planet.
As the binary message sewn into Curiosity’s parachute declares, “Dare mighty things.”