Seven minutes of terror
This article is an adaptation of our weekly Science newsletter that was originally sent out on February 17, 2021. Want this in your inbox? Sign up here.
By Victoria Jaggard, SCIENCE executive editor
Acronyms can be funny things. Depending on your life experience, the letters EDL might mean an airport code in Kenya, an IBM computer programing language, or, most distressingly, a hyper-nationalist group in the U.K. But most space geeks think of EDL as shorthand for the crucial mission phase called entry, descent, and landing—also known among Mars aficionados as the seven minutes of terror.
You may be hearing both terms a lot over the next few hours, as NASA prepares to put its next flagship rover, Perseverance, safely on the red planet. Around 3:50 p.m. ET on Thursday, the one-ton space robot will attempt a daring landing that involves hurtling into the Martian atmosphere at about 12,100 miles an hour, dropping briefly in freefall from its protective capsule, using thrusters to slow its descent and guide it to a safe landing zone, and then being lowered to the surface at a gentle two miles an hour by a giant crane.
The space agency has only pulled off this maneuver once before, when the “sky crane” system set down the Curiosity rover in Gale Crater in 2012. It worked then, but there’s no guarantee it will work now. Engineers chose the landing zone for Curiosity in part because it is an expanse of relatively flat terrain—a perfect “parking lot” free of hazards. By contrast, the landing zone for Perseverance, inside a dried-out lakebed called Jezero Crater, is filled with boulders and cliffs that could spell doom for an unprepared rover.
This time, the spacecraft in question is headed down with detailed onboard maps and a suite of cameras that should help it avoid catastrophe. That technology has “revolutionized how we approach landing sites,” USGS mapmaker Robin Fergason recently told our Nadia Drake. “For the first time we can have far more hazards in our landing ellipse than we’ve ever had before.”
Still, anything could happen during the many complex phases of this landing attempt, so engineers and space fans—myself included—will be holding their collective breath as Perseverance starts its dive tomorrow. The EDL process lasts for about seven minutes, and because it can take between five and 20 minutes for radio signals to get from Mars to Earth, the world won’t know if it worked until it’s all over. (Pictured at top, an early, blurry image of Mars.)
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TODAY IN A MINUTE
Vintage genes: Mammoth teeth found in Siberia in the 1970s have yielded the oldest DNA ever sequenced, including some samples more than a million years old, Michael Greshko reports for Nat Geo. At nearly twice as old as the previous record—a roughly 700,000-year-old horse genome—the mammoth genes break through a symbolic barrier for the ancient DNA field, demonstrating just how far scientists can peer back into life’s past. “It opens a new time window, so to say,” says lead study author Tom van der Valk. This finding also helps explain how North America’s now-extinct mammoths came to be. The new sequences suggest that North America’s Columbian mammoth—a bigger, more temperate-adapted cousin of the woolly mammoth—arose 400,000 to 500,000 years ago when Siberian woolly mammoths interbred with a previously unknown lineage revealed through DNA. (Pictured above, a museum worker checking the hair of a woolly mammoth replica in British Columbia.)
Junk or treasure? The collapse of the path-breaking Arecibo radio telescope in December has left 900 tons of wreckage on the hillsides of Puerto Rico. But the vital history of the site gives this wreckage value as important cultural artifacts of scientific history, argues Norman Sperling for Astronomy.com. Museums, institutions, and fans might want to exhibit or own pieces, he writes. In case you missed it, here’s Nat Geo’s Nadia Drake on why the collapse of Arecibo is a personal loss as well.
The excavation must wait: Who doesn’t want to know more about one of Africa’s most spectacular fossil caches, the prehistoric graveyard of flying reptiles, an “armored dog,” and 11 long-necked species still to be identified? There’s a catch to this cache: Digging is halted in Niger as it battles resurgent COVID-19 and escalating Islamist rebellions, the Washington Post reports. The hope is that the discoveries will be shown in two museums in Niger, says paleontologist and Nat Geo Explorer Paul Sereno. “The best place for priceless specimens in any country is on display,” Sereno said.
Unequal cost: Higher cancer and asthma rates are two costs of living closer to oil and gas facilities, and Black Americans are 75 percent more likely to live in close proximity. That’s just one way in which people of color are disproportionately affected by poor environmental conditions, writes the Guardian. The new outlet has launched a yearlong report on U.S. environmental racism. The series will examine a pipeline proposed to run through Brooklyn communities of color, the history of industrial pollution in Chicago, disparities in temperature, and radioactive uranium mining waste in the Navajo Nation.
INSTAGRAM PHOTO OF THE DAY
Dark sky: Where is photographer’s Babak Tafreshi’s favorite observatory to take in the stars? La Palma in the Canary Islands, where he holds a photo workshop most years. “The enchanting beauty of the island, with a massive caldera and stunning sky, is unique,” he tells us. The Roque de los Muchachos Observatory stands at 2,400 meters (7,874 feet) high on the island. In the photo above, the William Herschel Telescope is shining a laser into the upper atmosphere as part of the instrument’s adaptive optics system, which removes the blurring effect caused by air turbulence.
THE NIGHT SKIES
Moon meets Mars: On the same day NASA attempt to land its next rover on Mars, sky-watchers will get to observe the red planet for themselves with the moon right next to it. The distinct orange color of Mars is readily evident to our unaided eyes and is caused by all the iron oxide in Martian dust and soil—the same chemistry that makes rust here on Earth. Look for Mars and the moon in the southwestern skies after nightfall. — Andrew Fazekas
THE BIG TAKEAWAY
Mountain mystery: Why did Earth’s mountain’s stop growing for a billion years? A new study suggests that the planet’s continental crust thinned during that time, slowing the flow of nutrients into the sea and possibly stalling the evolution of life. “At its most slender, the land was about a third thinner than it is today—a change that researchers suggest may have been caused in part by a slowdown in plate tectonics,” Nat Geo’s Maya Wei-Haas writes. (Pictured above, the Appalachians in the southeast United States are slowly shrinking as weathering erodes them and plate tectonics no longer drives them up.)
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THE LAST GLIMPSE
In praise of accuracy: Artist and amateur astronomer Nathaniel Green drew the most detailed, accurate maps of Mars of his time (above, from 1877). However, a rival drew flashier, fanciful, and, ultimately false impressions of the planet that eclipsed Green’s work—and captured imaginations. This cartographic feud drove more than a century of speculation about our neighboring planet that still reverberates through our visions of Mars today. In this story, Nat Geo’s Nadia Drake gives Nathaniel Green his due.
Related: What would it be like to live on Mars? Try this simulation.
This newsletter has been curated and edited by David Beard, with photo selections by Jen Tse. Kimberly Pecoraro and Gretchen Ortega helped produce this. Have an idea or a link? We’d love to hear from you at david.beard@natgeo.com. Thanks for reading, and have a good week ahead.
