Friday, February 19, 2021

‘Touchdown Confirmed!’ Perseverance Landing Marks New Dawn For Mars Science

It’s a new day on Mars. NASA’s $2.7 billion Perseverance rover has successfully landed in Jezero crater, alighting just 35 meters away from hazardous boulders it had identified during descent. At about 3:55 p.m. EST, confirmation came back of the rover safely touching its wheels down, resulting in exuberant but socially distanced applause from double-masked engineers at the mission’s control room at the Jet Propulsion Laboratory (JPL).

“Touchdown confirmed,” said Swati Mohan, the JPL engineer narrating the landing attempt. “Perseverance is safely on the surface of Mars!” Soon after, a camera returned the first image, showing dust, rocks, and the shadow of the rover looming over the black-and-white martian surface.

The rover landed some 2 kilometers southeast of Jezero’s fossilized delta, locating a safe flat spot, tilting only 1.2°, amid a field of hazards (a map in the control room showed spots of safe green swarmed by dangerous red). “We did successfully find that parking lot, and have a safe rover on the ground,” said Allen Chen, the head of the rover’s landing team at JPL. The region is informally dubbed “Canyon de Chelly,” after a national monument in Navajo tribal lands.

The mission marks the start of a long-standing quest for Mars scientists: to gather rock samples and return them to Earth, where they will be probed for signs of life and clues to the planet’s past warm-and-wet climate.

The rover’s descent was as dramatic as it was choreographed. Plunging through the martian atmosphere while experiencing temperatures of up to 1300°C, the rover deployed a parachute as big as a basketball court as it approached its 7-kilometer-wide landing zone, the most precisely targeted of any NASA Mars lander. After identifying a safe haven free of dunes and boulders, the rover and its sky crane—a sort of rocket-propelled hovercraft—detached from the parachute.

The sky crane, falling at a walking pace, unspooled the rover to the surface with nylon cords. Finally, moments before touchdown, the rover deployed its six cleated aluminum wheels. The sky crane cut the cords and flew off to crash a safe distance away. The news, relayed by NASA’s Mars Reconnaissance Orbiter with an 11-minute delay, was greeted with cheers by those in JPL’s control room. Mars had a new martian.

The touchdown marks NASA’s ninth successful landing on the martian surface out of 10 tries. The Soviet Union is the first and only other nation to have performed the feat, in 1971, when its Mars 3 lander survived for 2 minutes. China, whose Tianwen-1 arrived at Mars a week ago, will attempt to put a rover and lander on the surface in several months.

Perseverance’s landing is likely to ensure additional attempts: NASA and the European Space Agency have begun to develop the two multibillion-dollar missions, which could launch in 2026 or 2028, needed to collect the samples gathered by Perseverance. If the samples make it to Earth a few years after that, researchers will analyze them for signs of life that could be preserved in fossilized microbial mats or, more likely, a lumpy distribution of organic molecules. Other minerals could capture the frozen imprint of the martian magnetic field as it failed, which allowed the ancient atmosphere—and, presumably, the warm climate—to escape to space.

Jezero crater is a great place to look for those clues: It holds a playground of habitable environments. Some 3.8 billion years ago, a thicker and warmer martian atmosphere allowed water to flow on the surface: One river penetrated Jezero, creating a delta of sediments and filling the crater nearly to the rim with water. Life could have found a niche in delta deposits, ancient shorelines, or hydrothermal springs exposed in the crater wall—all of which the rover should reach in its first 2 years of operation as it climbs up from the crater floor. It’s a “4-billion-year window into planetary evolution,” says Katie Stack Morgan, the mission’s deputy project scientist at JPL.

Perseverance’s first picture, taken through a transparent lens cap from underneath the rover, shows it avoided hazardous boulders.

But first the rover rests. Today is Sol 0, as one martian day is called. Perseverance will sit still after the landing, peering through transparent dust covers on its cameras to assess its location and erecting its high-gain antenna, used for direct communication to Earth. And then it will take a nap, using its radioactive thermoelectric generator to recharge its batteries, says Jennifer Trosper, the mission’s deputy project manager at JPL. “The rover’s had a long day.”

Over the next few days, the rover will raise its mast 2 meters above the surface and its main cameras will fix on the Sun, orienting the rover. The team will begin to image the landing site and the rover itself, checking the health of its instruments. By early next week, any video or audio captured during the rover’s landing should be relayed to Earth, the first time any Mars landing has been captured in such detail.

Each martian sol is half an hour longer than 1 day on Earth. To maximize the robot’s operations during daylight hours, the rover team will operate on “Mars time” for the first few months. Eventually, that will cause team members to experience a sort of perpetual jet lag, with team members sleeping during the day and working at night. And, unlike the similar schedule used for Curiosity—Perseverance’s predecessor that landed in 2012—engineers and scientists will largely work from home because of social distancing guidelines. Trosper, a veteran of several rover missions, is ready for the upheaval to her schedule: “I finally purchased a sleep mask,” she says. (She already had earplugs.)

Over the next month, the rover will remain in a commissioning phase. Its five-jointed, 2-meter-long robotic arm, which carries the rover’s rotary-percussive coring drill and several of its most sensitive cameras, will be extended and put through “calisthenics.” And a second robotic arm—this one inside the rover’s gut and designed to manipulate its cache of 43 stored ultraclean sample tubes—will be run through its paces. Sometime after that, it will conduct a first 5-meter test drive.

The first order of business after the monthlong commissioning phase will be loosing the 1.8-kilogram Ingenuity helicopter, currently attached to the rover’s belly. The pint-size Ingenuity is a technology demonstration, a bid to fly a rotor-powered vehicle on another planet for the first time. Perseverance will drive to flat terrain and drop Ingenuity to the surface. The helicopter will then furiously spin its rotors to ascend in the thin martian air. Four additional flights could follow, with the copter expected to have a total of 30 days to demonstrate its chops. “It will be truly a Wright brothers moment, but on another planet,” says MiMi Aung, Ingenuity's project manager at JPL.

After that, Perseverance’s science campaign, which includes an international team of 450 researchers, can begin in earnest. The rover will travel at a swift pace compared with Curiosity, capable of driving 200 meters per day thanks to improved automation and upgraded wheels. By the end of its 2-year primary mission, the team aims to collect at least 20 rock samples. The team has already scouted several possible routes, and the first drilling is likely to come this summer, says Ken Farley, the mission’s project scientist and a geologist at the California Institute of Technology.

The rover landed near a divide between two geological units on the lakebed targeted by the mission. One, the “mafic floor unit,” is potentially volcanic, believed to sit below the lakebed, marking an eruption that occurred before the water arrived. Such rocks contain trace radioactive elements that decay at a certain rate, so lab scientists on Earth could date the eruption and bracket the age of the lake.

The other rocks are rich in olivine and carbonate, potentially formed by ash deposited onto the crater after the water vanished. If the ash is also volcanic, those dates could constrain the lake’s demise. Put together, the two dates would tell a reliable story of the formation of the lake and delta and this wetter period in Mars’s history.

But the geology of each layer— inferred from orbit—is deeply uncertain, with scientists not even agreeing on the order in which they were deposited. That’s why, Farley says, the team is likely to target this boundary. “This is a great place to be because one of the things that scientists love to do is look to see how two different geologic units come together.”

After exploring that interface, the cliffs of Jezero’s fossilized delta will then loom; the fine-grained clay-bearing mudstones buried there would be a natural target. “The delta,” Farley says, “is what brought us to this location in the first place—a spectacular piece of geology.” On Earth, such clays blanket living things and preserve them as fossils. In similar clays at Gale crater, the Curiosity rover—which remains operational—detected traces of complex organic compounds that resembled kerogen, the feedstock of oil. But it could not determine whether the compounds were produced by ancient life or deposited by meteorites.

No comments:

Post a Comment