Mars rover's sampling campaign begins

doi:10.1126/science.373.6554.477

GSTDTAP > 气候变化

DOI	10.1126/science.373.6554.477
	Mars rover's sampling campaign begins
	Paul Voosen
	2021-07-30
发表期刊	Science
出版年	2021
英文摘要	After months of spaceflight, an 8-minute plunge to the surface of Mars, and weeks of exploration, NASA's Perseverance rover is beginning its primary scientific task: drilling out finger-size cores of martian rock for return to Earth. If all goes well, the first drilling sample will be collected from Jezero crater, a former lakebed, by early August. Perseverance has operated well since its February landing, and it recently tested its rock storage system, using its robotic arm to stow a sampling tube into its guts. There the empty tube was imaged and then sealed for storage. “The great news is that it all worked perfectly,” says Jennifer Trosper, Perseverance's project manager at NASA's Jet Propulsion Laboratory. “We are ready to sample.” Now, 1 kilometer south of its landing site, Perseverance has reached an array of what its operating team calls paver stones—flat, white, dust-coated rocks found throughout much of the floor of Jezero crater. Here, on what is believed to be the most ancient terrain in the crater, nearly 4 billion years old, the team will direct the rover to drill and collect its sample, targeting a rock that is average in chemistry, mineralogy, and texture. The chalk-size core will be stored in an ultraclean metallic tube, one of 38 samples the rover will eventually collect, with about 30 of those likely to be returned to Earth by later missions. It will reside in the rover's belly until it is deposited in a cache on the surface near the crater's rim a year and a half from now. Whether the paver stone landscape was deposited by the lake or formed by volcanic flows isn't clear. But if it is volcanic, it might have trapped radioactive elements that a lab on Earth could analyze to determine accurate dates for the lake's existence. The drill operators don't know what to expect because the rocks are covered with sand grains and pebbles, along with some sort of purplish coating, says Ken Farley, the mission's project scientist and a geologist at the California Institute of Technology. But before drilling into the pavers, the rover will unleash one instrument that could help answer this puzzle: an abrasion bit mounted at the end of its 2-meter-long arm. After grinding into the rock, the arm will blow compressed gas to clear away the grit, giving a clear glimpse of the underlying rock. The rover can then use its arm-mounted camera and laser and x-ray probes to probe its structure and mineralogy. “I'm pretty confident we will be able to answer this question,” Farley says. Perseverance has already spotted other tantalizing sites to explore and sample in Jezero crater. In the ancient delta to its west that is the rover's destination next year, its cameras have revealed distinctive layered deposits that show the lake was high, quiet, and stable for a long time, Farley says. Above those layers lie 1-meter-wide smooth boulders that could only have been carried by floodwater later in the lake's history. This suggests the lake could have seen distinct phases in its life, which fits with a larger picture of the planet's history in which lakes were common billions of years ago, then gave way to periodic floods after the climate cooled, Farley says. A long-lived lake might have also provided the nutrients and habitat to fuel life, says Kennda Lynch, an astrobiologist at the Lunar and Planetary Institute who is unaffiliated with the mission. “This is great. I feel more confident we chose the right place to go.” Samples and measurements from Perseverance's next target, Séítah, a region of sand dunes and ridges to its west that the car-size rover has skirted past, could test that picture. Seen from orbit to be rich in olivine, a volcanic mineral, and carbonates, which can form when olivine is exposed to water and carbon dioxide, Séítah has unexpectedly complex geology, including layered terrain that might preserve signs of past life or patterns of water flow. But the rover can't drive into it without getting stuck in the dunes, so the Perseverance team devised an incursion from above and behind to access its secrets. First, the rover's miniature Ingenuity helicopter, in its ninth flight earlier this month, scouted across Séètah in a 625-meter journey, breaking records for flight duration and speed before landing on the other side of the dunes. The helicopter photographed the intersection of Séètah with the paver unit that Perseverance is now exploring—a boundary that could reveal whether the pavers continue beneath Séitah's dunes, an important fact if a volcanic date is found. And it also scouted fractures that could hold evidence of whether ancient subsurface habitats existed in Jezero. Meanwhile, from afar, Perseverance has spied fine layering in Séítah's ridges, including a prominent 40-meter-tall plateau dubbed Kodiak that, in all likelihood, marks the delta's incursion into the lakebed. Such layers could be caused by mudstones, which smother and preserve life on Earth. But the layers could have a volcanic origin, as well—and so the rover will loop south around Séètah later this year, nudging into a flat space where it can safely sample and tease out that story. Once the Séítah campaign is done, Perseverance will backtrack all the way north to its landing site, “putting the pedal to the metal,” Trosper says. From there it will continue north then west on a safe route to the looming cliff of the main delta—and the life-trapping muds entombed within it.
领域	气候变化 ; 资源环境
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/335516
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Paul Voosen. Mars rover's sampling campaign begins[J]. Science,2021.
APA	Paul Voosen.(2021).Mars rover's sampling campaign begins.Science.
MLA	Paul Voosen."Mars rover's sampling campaign begins".Science (2021).