By The Washington Post · Joel Achenbach, Sarah Kaplan, Ben Guarino
"Touchdown confirmed! Perseverance is safely on the surface of Mars, ready to begin seeking the signs of past life," announced Swati Mohan, the guidance and control operations lead for the mission at the NASA Jet Propulsion Laboratory in Pasadena, Calif.
Cheers, clapping and fist-pumps erupted in the control room, which was half-empty because of the coronavirus pandemic. Someone shouted: "TRN, TRN," referring to the "terrain relative navigation" system that allowed Perseverance to land in a rugged area full of natural hazards.
Perseverance, the first multibillion-dollar NASA mission to Mars in nine years, quickly produced two low-resolution images of the landing site - a forlorn landscape pocked with small craters. Dust kicked up by the landing covered the glass shields on the cameras. The pair of photos showed the rover casting a shadow on the Martian landscape.
Perseverance used its autonomous guidance system to avoid hazardous terrain in the target area, an ancient lake bed known as Jezero Crater. The touchdown followed the "seven minutes of terror" - in homage to the emotional state of engineers rooting for success. Mars is a notoriously difficult place to land a spacecraft.
Going back more than half a century, about half of all robotic missions to the planet have failed, although NASA appears to have mastered the feat over the past two decades. The rover Curiosity, which landed in 2012 far to the east of Perseverance's location, remains operational. Perseverance is similar in scale but is slightly heavier and has about 50 percent more scientific instrumentation, according to NASA.
The vehicle carrying Perseverance entered the Martian atmosphere at 12,000 mph, used a heat shield to avoid burning up, then deployed a 70-foot-diameter parachute while still going nearly twice the speed of sound. Finally, the craft used rocket thrusters to slow down further and then a system known as a sky crane to lower the rover the final distance to the surface.
The landing on rough terrain is the most hazardous phase of the mission. The entry, descent and landing had to be accomplished entirely autonomously. Mars is too far from Earth to permit technicians to joystick the landing; a signal between the spacecraft and Pasadena takes 11 minutes at the speed of light.
For that reason, the spacecraft was loaded with navigation software to guide it to a safe spot in an area that features 200-foot cliffs, gullies, boulders and sand-filled craters that could potentially immobilize it.
The rover touched down in a relatively rugged area, about a mile southeast of the center of its target. In this treacherous environment, the autonomous navigation system proved "absolutely essential," entry, descent and landing lead Allen Chen said at a news conference Thursday evening.
"We found the parking lot, and hit it," Chen said, avoiding dangerous terrain all but certain to doom the rover. The vehicle is almost level, tilted only a matter of a degree.
Project scientist Ken Farley said the site is on the boundary between rock regions representing two important moments in Mars' geologic history. Off in the distance, images seem to show the cliffs of the river delta.
"This is a great place to be," he said.
But there is still a "ripple field" - sand dunes - between the rover and the delta that scientists want to explore. The rover may have to drive around those sand dunes to get to the delta formation.
Thursday's landing was just the latest hurdle for a mission fraught with obstacles. The spacecraft's journey to the launchpad had been complicated by the coronavirus pandemic, which pushed much of NASA's workforce to go remote. Twenty minutes before Perseverance was scheduled to take off from Cape Canaveral, Fla., last July, an earthquake rocked mission control in Pasadena.
But after a six month, 293-million-mile journey, the spacecraft hit the Martian atmosphere at 3:48 Eastern time Thursday afternoon - exactly on schedule.
"Yes, yes, yes, yes," someone could be heard quietly chanting over the NASA live stream.
Engineers briefly lost contact with the spacecraft amid the tremendous heat of its descent. At maximum deceleration, the craft experienced force 10 times the force of gravity on Earth.
A minute later came the first sign that this landing was going well: "Parachute deployed."
There was a burst of applause, before engineers settled back to anxious silence.
The spacecraft jettisoned its heat shield. Its radar locked onto the ground. It turned on its navigation system and deployed the sky crane.
And then came the words they'd all been waiting for: "Tango Delta." TD. Touchdown.
And, finally, "Nominal."
Perseverance had arrived safely on Mars.
"The vehicle is going on a roller-coaster ride and you are too," Chen said afterward. "You're second guessing yourself as you go, even though it's already happened."
With the rover safely deposited at its landing site, the sky crane flew away and crash-landed elsewhere on the Martian surface.
Now begins the rover's "commissioning" phase, when engineers examine every inch of the vehicle's machinery to make sure it is ready for the mission. The rover will practice driving, test its robotic arm and update its software. Engineers who care for the vehicle will switch to "Mars time" - organizing their lives according to the Red Planet's 24-hour, 37-minute day.
Roughly 30 Martian days (or "sols") from now, Perseverance will drive to a flat area that can serve as the flight pad for Ingenuity, a tiny solar powered helicopter. NASA will take another 30 sols to fly Ingenuity around the area, testing out the never-before-used autonomous flight technology.
Next comes the central part of the rover's mission: exploring Jezero Crater. Perseverance has automated driving technology that allows it to navigate obstacles without help from the ground. It is expected to cover more ground than any previous Mars rover - an average of about 650 feet per Martian day.
Typically, Mars landings are cause for great pomp and circumstance at the Jet Propulsion Laboratory. The Pasadena campus swarms with scientists, journalists and schoolchildren. Huge projectors show a live steam from mission control. A tradition dating to the 1960s demands that a jar of peanuts be on hand at the space flight operations facility - supposedly the snack brings good luck.
Thursday's events were more subdued, with only a minimal crew of ground controllers on site for the landing.
But fans of the mission found socially distant ways to celebrate. In Switzerland, where NASA science chief Thomas Zurbuchen grew up and where the rover's motors were produced, artist Gerry Hofstetter projected images of the rover, Mars and the NASA logo onto an Alpine mountaintop.
Though led by NASA, the mission is an international endeavor. The rover's instruments are operated by scientists in three countries, and the Mars Sample Return program is a partnership with the European Space Agency.
Perseverance's new home is a narrow band of flat terrain that lies along the cliffs that delineate the elevated remnants of a river delta - all within Jezero Crater. The river delta is considered one of the best places on Mars to search for signs of ancient life.
Today, the crater is a bleak expanse of rock canyons and windswept sand. With no magnetic field to protect it, the planet's surface is bombarded by solar radiation. The air is thin and mostly carbon dioxide. Nighttime temperatures plunge to minus-100 degrees Fahrenheit. It is hardly a hospitable environment.
But roughly 4 billion years ago, Mars looked a lot like ancient Earth. It boasted volcanic activity, a thick atmosphere and temperatures balmy enough to maintain liquid water on its surface.
In those days, Jezero Crater contained a vast lake. The surrounding canyons were carved by mighty rivers. The feature that Perseverance is scheduled to inspect was a delta, where sediments from the surrounding watershed accumulated in layers of mud. On Earth, such sediments have preserved evidence of ancient life in the form of fossilized mats of microscopic pond scum called "stromatolites."
"If we could find something like that on Mars, that would be the holy grail for astrobiology," said Purdue University planetary scientist Briony Horgan, a member of Perseverance rover's science team. Horgan has led satellite surveys of the landing site that showed it is rich with the kinds of molecules known to help preserve the signatures of living organisms.
Perseverance is armed with a battery of instruments designed to detect biosignatures. Two cameras will photograph the landscape and zoom in on tiny structures. A sensor will use X-rays to measure the chemical makeup of rocks while a machine mounted on the robot's arm deploys lasers to detect organic molecules and other potential biosignatures. Ground-penetrating radar will map the subsurface, and a Martian weather station will take in data about temperature, wind and clouds of dust.
Many of these are more advanced versions of the instruments on the Curiosity rover, which has been exploring a spot far to the east of Jezero since 2012.
But Perseverance is the first NASA rover with the capacity to collect samples of soil and rock and cache them on the Martian surface. If and when the space agency is able to launch follow-up missions, those spacecraft will retrieve Perseverance's samples and bring them back to Earth, where they can be analyzed with even more sophisticated tools in the world's top labs.
"Finding a sample suite that is worth bringing back is really important," said Ken Farley, project scientist for the mission. "What's at stake is the ability to really make the first step in answering the question of whether life exists elsewhere."
"Astrobiologists have been dreaming about this mission for decades," said Mary Voytek, who directs NASA's astrobiology program. Microbiologists like her have found life on Earth virtually wherever they've looked. Perseverance will play the role of robotic microbiologist on Mars.
It is unlikely images alone will be considered definitive proof of ancient life. Nor is it possible to miniaturize all the equipment necessary for the most detailed examinations of Martian samples. That's why Perseverance is part of a broader project to gather samples of Mars that can eventually be returned to Earth.
There are dozens of sterilized tubes, designed to house chalk-size samples, tucked within the belly of the Perseverance robot. The rover will drill into Mars, secure rock and mineral samples in the tubes, seal the tubes and cache them for a future mission to retrieve.
A follow-up robotic lander assigned to retrieve the samples must descend to within 100 yards of where Perseverance deposits the sample cache, said Bobby Braun, the sample return program manager, on Wednesday. The retriever will, in turn, hand off samples to a cargo spacecraft in orbit over Mars. This will be the largest craft ever sent to the Red Planet, in part because it will have to carry enough propellant for a return trip.
Some of the scientists who will study those samples in the 2030s, in a facility that has not yet been built, may currently be students - or even children, said Elisabeth Hausrath, a University of Nevada Las Vegas astrobiologist who is assigned to represent the interests of those future scientists.
Detecting undisputed evidence of life in Martian rocks would be a spectacular scientific discovery - perhaps the most important humanity has ever made. It would suggest that still more life could exist somewhere else.
The discovery might also remind humanity that life is not indestructible. If a changed environment is what doomed organisms on Mars, it could happen here, too.
"These types of discoveries have the ability to affect people to their core," said Kathryn Stack Morgan, deputy project scientist for the mission. "It becomes something you have to confront about yourself and your species and your place in the universe."
Other members of the team had a more quotidian take on the day's events. John McNamee, the mission's project manager, told reporters Thursday that he slept soundly the night before; he knew his engineers would guide Perseverance to a smooth landing.
"Then I got up, had a little exercise, had breakfast and landed on Mars," he said. "So, a pretty good day so far."