A selfie taken by Nasa's Perseverance rover over a rock nicknamed "Rochette" in September. Photo / Nasa/JPL-Caltech/MSSS via The New York Times
The past 12 months on Mars have been both "exciting" and "exhausting" for scientists and engineers minding the Perseverance rover and Ingenuity helicopter. And the mission is only really getting started.
A year ago, Nasa's Perseverance rover was accelerating to a collision with Mars, nearing its destination after a 290-million-mile, seven-month journey from Earth.
Last February 18, the spacecraft carrying the rover pierced the Martian atmosphere at 20,920km/h In just seven minutes — what Nasa engineers call "seven minutes of terror" — it had to pull off a series of manoeuvres to place Perseverance gently on the surface.
Given the minutes of delay for radio communications to crisscross the solar system, the people in mission control at Nasa's Jet Propulsion Laboratory in California were merely spectators that day. If anything had gone wrong, they would not have had any time to attempt a fix, and the US$2.7 billion mission — to search for evidence that something once lived on the red planet — would have ended in a newly excavated crater.
But Perseverance performed perfectly, sending home exhilarating video footage as it landed. And Nasa added to its collection of robots exploring Mars.
"The vehicle itself is just doing phenomenally well," said Jennifer Trosper, project manager for Perseverance.
Twelve months later, Perseverance is nestled within a 45km-wide crater known as Jezero. From the topography, it is evident that more than 3 billion years ago, Jezero was a body of water roughly the size of Lake Tahoe, with rivers flowing in from the west and out to the east.
One of the first things Perseverance did was deploy Ingenuity, a small robotic helicopter and the first such flying machine to take off on another planet. Perseverance also demonstrated a technology for generating oxygen that will be crucial whenever astronauts finally make it to Mars.
The rover then set off on a diversion from the original exploration plans, to study the floor of the crater it landed in. The rocks there turned out not to be what scientists were expecting. It ran into trouble a couple of times when it tried to collect cores of rock — cylinders about the size of sticks of chalk — that are eventually to be brought back to Earth by a future mission. Engineers were able to solve the problems and most everything is going well.
"It's been a very exciting year, exhausting at times," said Joel Hurowitz, a professor of geosciences at Stony Brook University in New York and a member of the mission's science team. "The pace of work has been pretty incredible."
After months of scrutinising the crater floor, the mission team is preparing for the main scientific event: investigating a dried-up river delta along the west rim of Jezero.
That is where scientists expect to find sedimentary rocks that are most likely to contain blockbuster discoveries, maybe even signs of ancient Martian life — if any ancient life ever existed on Mars.
"Deltas are, at least on Earth, habitable environments," said Amy Williams, a geology professor at the University of Florida and a member the Perseverance science team. "There's water. There's active sediment being transported from a river into a lake."
Such sediments can preserve carbon-based molecules that are associated with life. "That's an excellent place to look for organic carbon," Williams said. "So hopefully, organic carbon that's indigenous to Mars is concentrated in those layers."
Perseverance landed not much more than a mile from the delta. Even at a distance, the rover's eagle-eyed camera could make out the expected sedimentary layers. There were also boulders, some as large as cars, sitting on the delta, rocks that were washed into the crater.
"This all tells a fascinating story," said Jim Bell, a planetary scientist at Arizona State University.
The data confirm that what orbital images suggested was a river delta is indeed that and that the history of water here was complex. The boulders, which almost certainly came from the surrounding highlands, point to episodes of violent flooding at Jezero. "It wasn't just slow, gentle deposition of fine grained silt and sand and mud," said Bell, who serves as principal investigator for the sophisticated cameras mounted on Perseverance's mast.
Mission managers had originally planned to head directly to the delta from the landing site. But the rover set down in a spot where the direct route was blocked by sand dunes that it could not cross.
The geological formations to the south intrigued them. "We landed in a surprising location, and made the best of it," said Kenneth Farley, a geophysicist at the California Institute of Technology who serves as the project scientist leading the research.
Because Jezero is a crater that was once a lake, the expectation was that its bottom would be rocks that formed out of the sediments that settled to the bottom.
But at first glance, the lack of layers meant "they did not look obviously sedimentary," said Kathryn Stack Morgan of Nasa's Jet Propulsion Laboratory and who is the deputy project scientist. Nothing clearly suggested they were volcanic in origin either.
"It's really turned into a detective story sort of about why this region is one of the most geologically unusual in the planet," said Nicholas Tosca, a professor of mineralogy and petrology at the University of Cambridge in England and a member of the science team.
As the scientists and engineers contemplated whether to circle around to the north or to the south, the team that built a robotic helicopter named Ingenuity got to try out their creation. The helicopter was a late addition to the mission, meant as a proof-of-concept for flying through Mars' thin air.
On April 18, Ingenuity rose to a height of 3 metres, hovered for 30 seconds and then descended back to the ground. The flight lasted 39.1 seconds. Over the next weeks, Ingenuity made four more flights of increasing time, speed and velocity.
That was supposed to be the end of Ingenuity's mission. Perseverance was to leave it behind and head off on its research.
But Nasa decided five flights were not enough. When Perseverance set off to explore the rocks to the south, Ingenuity went along, scouting the terrain ahead of the rover. That helped avoid wasting time driving to unexceptional rocks that had looked potentially interesting in images from orbit.
"We sent the helicopter and saw the images, and it looked very similar to where we were," Trosper said. "And so we chose not to drive."
The helicopter just completed its 19th flight, and it remains in good condition. The batteries are still holding a charge. The helicopter has shown it can fly in the colder, thinner air of the winter months. It was able to shake off most of the dust that fell on it during a dust storm in January.
"Everything's looking green across the board," said Theodore Tzanetos, who leads the Ingenuity team at the Jet Propulsion Laboratory.
In the exploration of the rocks to the south of the landing site, scientists solved some of their secrets when the rover used its drill to grind shallow holes in a couple of them.
"Oh, wow, these look volcanic," Stack Morgan said, remembering her reaction. "Exactly what you'd expect for a basaltic lava flow."
The tools that Perseverance carries to study the ingredients of Martian rocks can take measurements pinpointed on bits of rock as small as a grain of sand. And cameras on the robotic arm can take close-up pictures.
Those observations revealed large grains of olivine, an igneous mineral that can accumulate at the bottom of a large lava flow. Later, fractures emerged between the olivine grains that were filled with carbonates, a mineral that forms through interactions with water.
The thinking now is that the Jezero crater floor is the same olivine-rich volcanic rock that orbiting spacecraft have observed in the region. It might have formed before the crater filled with water.
Sediments from the lake probably did cover the rock, with water percolating through the sediments to fill the fractures with carbonate. Then, slowly, over a few billion years, winds blew the sediments away.
That the wispy air on Mars could erode so much rock is hard for geologists to wrap their minds around.
"You don't find landscapes that are even close to that on Earth," Farley said.
The most troublesome moments during the first year have occurred during the collection of rock samples. For decades, planetary scientists have dreamed that pieces of Mars could be brought to Earth, where they could study them with state-of-the-art instruments in laboratories.
Perseverance is the first step in turning that dream into reality by drilling cores of rock and sealing them in tubes. The rover, however, has no means to get the rock samples off Mars and back to Earth; that awaits another mission known as Mars Sample Return, a collaboration between Nasa and the European Space Agency.
During the development of Perseverance's drill, engineers tested it with a wide variety of Earth rocks. But then the very first rock on Mars that Perseverance tried to drill turned out to be unlike all of the Earth rocks.
The rock in essence turned to dust during the drilling and slid out of the tube. After several successes, another drilling attempt ran into problems. Pebbles fell out of the tube in an inconvenient part of the rover — the carousel where the drilling bits are stored — and that required weeks of troubleshooting to clean away the debris.
"That was exciting, not necessarily in the best way," Stack Morgan said. "The rest of our exploration has gone really well."
Perseverance will at some point drop off some of its rock samples for a rover on the Mars Sample Return mission to pick up. That is to prevent the nightmare scenario that Perseverance dies and there is no way to extricate the rocks it is carrying.
The top speed of Perseverance is the same as that of Curiosity, the rover Nasa landed in another crater in 2012. But improved self-driving software means it can cover longer distances in a single drive. To get to the delta, Perseverance needs to retrace its path to the landing site and then take a route around the sand dunes to the north.
It could arrive at the delta by late May or early June. Ingenuity will try to stay ahead of Perseverance.
The helicopter flies faster than the rover can drive, but after each flight, its solar panels have to soak up several days of sunshine to recharge the batteries. Perseverance, powered by the heat from a hunk of plutonium, can drive day after day after day.
The helicopter, however, might be able to take a shortcut across the sand dunes.
"We're planning to get to the delta," Tzanetos said. "And we're discussing what happens beyond the river delta."
But, he added that every day could be the last for Ingenuity, which was designed to last only a month. "You hope that you're lucky enough to keep flying," he said, "and we're going to keep that streak going for as long as we can."
Once Perseverance gets to the delta, the most electrifying discovery would be images of what looked to be microscopic fossils. In that case, "we have to start asking whether some globs of organic matter are arranged in a shape that outlines a cell," said Tanja Bosak, a geobiologist at the Massachusetts Institute of Technology.
It is unlikely Perseverance will see anything that is unequivocally a remnant of a living organism. That is why it is crucial for the rocks to be brought to Earth for closer examination.
Bosak does not have a strong opinion on whether there was ever life on Mars.
"We are really trying to peer into the time where we have very little knowledge," she said. "We have no idea when chemical processes came together to form the first cell. And so we may be looking at something that was just learning to be life."
This article originally appeared in The New York Times.
Written by: Kenneth Chang
© 2022 THE NEW YORK TIMES
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