At 7:50 a.m. ET, NASA’s Perseverance rover, bound for Mars, blasted off from Kennedy Space Center in Cape Canaveral, Florida. Soaring into the sky atop an Atlas V rocket, Perseverance is now settling in for its seven-month interplanetary flight. The rover’s target: Jezero Crater, the site of an ancient crater lake and an erstwhile river delta that the rover will scour for signs of past Martian life.
With its newest, $2.4-billion robot en route to Mars, NASA is setting out to answer a question that has nagged humanity for as long as astronomers have pointed telescopes at the reddish world: Is there—or was there once—life on our neighboring planet?
“Our strategy is to look very deep in time, back to this time when we believe Mars and Earth were much more similar,” says deputy project scientist Ken Williford of NASA’s Jet Propulsion Laboratory (JPL). “Studying Mars and its ancient environments—what can we learn about our place in the universe? Are we alone? Have we always been alone?”
But exploring Jezero won’t be easy. The first test for Perseverance will be a perilous, seven-minute plunge through the thin Martian atmosphere, scheduled for February 18, 2021. Surviving that risky descent means relying on a heat shield, a parachute, a new navigation system, and a hovering sky crane that will lower the rover to Jezero’s soil—all without any input from mission controllers on Earth. Once down, Perseverance will deploy a small, featherweight helicopter named Ingenuity, and over the mission’s first few weeks on Mars, the little chopper will find out whether powered flight in Mars’s thin air is within human capability.
“A vehicle to fly on Mars has to be really light, and it has to spin really fast,” Ingenuity project manager MiMi Aung says. Technologies such as composite materials and miniature electronics have only recently become advanced enough to even attempt the flight.
After releasing Ingenuity, the Perseverance rover will focus on its primary quest: Looking for signs of ancient life in the rocks and sediments strewn throughout the crater basin. Jezero might be frigid and inhospitable today, but scientists know the environment was warm and watery early in the planet’s history because liquid-formed features survive today. The rover carries a suite of sophisticated instruments that will scrutinize crater rocks for biological fingerprints, and an additional set of tools will let Perseverance collect and store samples for a future rover to fetch and return to Earth in the next decade or so.
“To actually have really carefully selected samples back at Earth, even though they’re small—it’s going to really change the way we do business,” says Sarah Stewart Johnson, a planetary scientist at Georgetown University who studies the biosignatures of ancient life. “And once we have those samples, we’ll have them forever,” allowing scientists to study them in the future with tools that don’t yet exist.
Perseverance is NASA’s first Mars rover with the explicit goal of searching for life. If all goes according to plan, the six-wheeled, nuclear-powered robot will finally let scientists back on Earth determine whether Mars once hosted ecosystems of its own—or find that the signatures of life are conspicuously absent from the planet.
Lessons from an alien desert
Perseverance was named by seventh-grader Alex Mather, from Northern Virginia, who thought the name captured an essential component of exploring extreme alien environments. Now on the cusp of a mission to determine once and for all whether life might have been common on Mars, the name Perseverance couldn’t be more apt.
For decades, scientists have searched for alien life-forms—but the field of astrobiology has only recently become mainstream science. Today, the field is booming. Perseverance is heading to Mars, future missions are targeting frozen moons in the outer solar system where life could thrive today, and labs on Earth are zeroing in on the origin of our own planet’s organisms.
While the Perseverance team thinks the rover will likely uncover tantalizing—if not definitive—evidence for Martian life, Katie Stack Morgan, the Mars 2020 deputy project scientist at JPL, says the alternative would be just as captivating.
“I’m optimistic that when those samples come back, we will find compelling evidence for ancient life,” she says. “It should be there, and if it’s not, then that says something really interesting about the conditions in which life can actually exist on another planet.”
Perseverance joins the fleet
This month, three spacecraft set sail for Mars. On July 19, the United Arab Emirates launched its Hope orbiter, and on July 23, China’s Tianwen-1 spacecraft blasted off.
The deep space flotilla is the result of a favorable planetary alignment that occurs every 26 months, when the journey from Earth to Mars can be undertaken with a minimum expenditure of fuel. Had the ongoing coronavirus pandemic postponed today’s launch, NASA would have needed to safely (and expensively) store Perseverance until the planets align again in more than two years.
The spacecraft is an upgraded, heavier version of NASA’s Curiosity rover, which landed in Mars’s Gale Crater in 2012 and has been studying the ancient crater environment ever since.
Weighing in at 2,260 pounds, with 3.5 miles of cable curled in its belly, Perseverance carries seven science instruments, 43 sample-collecting tubes, the first microphone to fly to Mars, and nearly two dozen cameras. A few tokens of humanity are also making the journey, including a plaque commemorating the medical community's work during the ongoing pandemic and a Morse-code inscribed message bearing the names of 11 million Earthlings who submitted their names to NASA.
After entering the atmosphere at 12,000 miles per hour, deploying a parachute, and then blasting away the heat shield, Perseverance will get its first look at Mars. While still careening toward the surface, the rover will activate a camera system that lets it autonomously avoid hazards near its landing site, such as rocks, slopes, or sand pits that could foil the mission.
“It’s the first mission to land with its eyes open,” says JPL’s Swati Mohan, the mission’s lead guidance, navigation, and control systems engineer. “We basically added a brain to the rover in order to do this.”
For 10 to 15 seconds, Mohan says, the rover will furiously snap images of the terrain racing by, guided by detailed onboard maps. The system will then autonomously align the rover’s view with established hazards and guide Perseverance to a safe point within its roughly six-mile-wide landing ellipse.
“It’s a region that is more hazardous than any we’ve landed on in the recent past,” Mohan says. “But Perseverance’s probability of landing safely is over 99 percent.”
Once the dust settles, the rover will begin to explore the dry lake of another world.
Announced as the rover’s destination in 2018, the 30-mile-wide Jezero Crater is home to a vast, branching river delta that formed as water trickled into an ancient crater lake and deposited sediments on its floor—exactly the type of material that could contain records of living organisms.
“Deltas are great at preserving organic matter and other types of biosignatures,” Tanja Bosak of the Massachusetts Institute of Technology and a member of the Perseverance science team said during a call with reporters.
Ancient Mars was nothing like the planet we see today. Data from numerous rovers and orbiters, including detailed topographic maps, mineral surveys, and other studies, suggest that for its first billion years, Mars was swaddled in a thick atmosphere and at least periodically warm and wet—a planetary oasis not unlike its Earthy neighbor.
In fact, until about 3.5 billion years ago, abundant lakes and rivers pooled and flowed over the planet’s surface. Today, we can see the handiwork of liquid in river-carved valleys, stream-sculpted pebbles, minerals that form in water, and piles of sediment deposited in basins and deltas.
Roughly 3.8 billion years old, Jezero—meaning ‘lake’ in Serbian, named for a town in Bosnia and Herzegovina—was filled with more than 800 feet of water. At nearly four billion years old, the rocks of the crater rim are among the oldest in the area, and the rocks in its basin are roughly 500 million years younger. By peering into the rocky record spanning such a broad time interval, scientists may glimpse the monumental shift in Martian planetary climate. Studying the dry lake will also provide a new tool to pinpoint the ages of other areas on Mars—which are currently estimated based on the number of surrounding craters.
Looking for dead Martians
Perseverance project scientist Ken Williford says the chances are good that the rover will uncover rocks that, even studied remotely, will “blow us away.”
In Jezero, clays called smectites could contain records of complex organic compounds, and carbonate deposits are strewn in the basin—exactly the type of rock that preserves the oldest signatures of life on Earth. Scientists think that if the lake’s chemistry was right, these carbonates might be similar to structures called stromatolites, which are layers formed by alternating sheets of microbes and muddy organic matter that record the presence of life on Earth going back 3.5 billion years.
But even on this planet, determining whether a fossil contains traces of microbial activity is tricky.
“We are still having huge debates over what qualifies as life when we push back into the rock record as far as we are pushing back into the rock record in Jezero Crater,” Stewart Johnson says.
In the ancient layers of Martian sediment, Perseverance will look for hints of former inhabitants using high-resolution cameras and two scientific instruments designed to closely scrutinize the rocks. Called PIXL and SHERLOC, these tools on the robot’s arm will capture detailed information about how elements, minerals, and organic compounds are distributed throughout the Martian rock.
"Life tends to be clumpy," Williford says. Stromatolites on Earth display layers rich in organics sandwiched between organic-poor layers, so finding similar patterns on Mars would be a strong sign of life.
Perhaps the mission’s best chance of clearly identifying life, however, will come from the rocky samples it gathers for future return to Earth. The rover will stuff some three dozen heat-reflecting tubes with about 15 grams worth of rock core each for a future rover to fetch, a joint mission between NASA and the European Space Agency (ESA) now planned to launch in 2026 and return no sooner than 2031.
“We have many powerful techniques in labs back here that can decode an enormous amount of information about the ancient environment from even a single grain of sand,” Williford says.
On Earth, those samples will be studied for a variety of biosignatures, including molecular complexity, carbon isotope ratios, and metabolic byproducts.
“Mars was habitable—but there’s still this big question of whether life took hold, and if it did, is it still there?” Stewart Johnson says. “We’re moving, finally, to actually looking for biosignatures, or traces of life.”
Paving the way for humans
Although looking for life is one of the rover’s main goals, it’s also carrying new technologies that could make it easier for humans to navigate and survive in the frigid, nearly airless Martian environment. One of these is an instrument called MOXIE that will convert noxious carbon dioxide into oxygen, a crucial resource for any habitable environment.
“When scaled up, that kind of capability could be used to provide oxygen that might support hab structures on Mars and be used to make the rocket fuel and propellant that could bring astronauts back to Earth,” Stack Morgan says.
Another first is Ingenuity, the four-pound helicopter snuggled up beneath the rover’s belly. The craft, engineered to fly in the wispy Martian air, aims to become the first vehicle to achieve powered flight on another planet, adding an aerial dimension to space exploration.
The helicopter’s two contra-rotating, carbon-fiber propellers span nearly four feet and spin 2,400 times per minute—faster than any helicopter on Earth. Ingenuity will carry several cameras as it performs autonomous flight tests during the first 30 days of the rover’s mission.
The team is now working out the details of the helicopter’s flight plans, with an initial 20-second excursion that will put the craft through its paces. If the first flight goes well, four increasingly complex flights are in the works—tests that could validate future Martian aircraft for navigation, scouting, and sample collecting.
“The focus is to get the data back from the flight,” Aung says. “How do we operate an aerial vehicle at Mars, remotely, from Earth? That entire thing is a learning experience.”
When it comes to Mars, humans have needed to learn about the planet from afar. But as helicopters and rovers and rock samples reveal more of its secrets, we might finally come to understand how habitable the world once was—and how we may inhabit it ourselves in the future.