Updated at 2:06 p.m. ET on Feb. 19, 2021.
When Mike Zolensky saw the night sky over the Australian desert glow red in June of 2010, he knew: The long-awaited object had plunged through the atmosphere and fallen to Earth.
Zolensky, a curator of astromaterials, and dozens of others leapt into action. The team dispatched a helicopter to find the fallen object in the darkness. At daybreak, elders from the local indigenous population arrived to check whether it had landed on any sacred sites. The next visitors wore helmets and protective gear, should the object explode, and carried spermicidal spray, in case it had cracked, releasing something alive. On top of everything else, they all had to watch out for kangaroos. “They’re all over the place,” Zolensky told me.
Later that day, the crew retrieved what had tumbled from the sky: tiny dust grains from a rocky asteroid tucked inside a little spaceship built by humans specifically to protect them.
These are the lengths that researchers have gone to in order to obtain a piece of the wonders beyond Earth, even microscopic particles about as small as a single human blood cell. And though these so-called sample-return missions are risky, with no guarantee of success, they’re booming. JAXA, the Japanese space agency, which retrieved those asteroid grains in 2010, made a second catch in Australia in 2018, from a different asteroid. China brought home moon samples last year. A NASA spacecraft will deliver more asteroid pieces in 2023, and a JAXA mission to Phobos, Mars’s largest moon, is already in development.
And today, a rover landed on Mars, carrying empty canisters to fill with rocks for its return to Earth someday, in what would be the first-ever sample return from another planet.
Scientists have wanted a piece of Mars for years. Not in the form of meteorites that fall to Earth—they have some of those already—but stuff right from the source. Cosmic radiation and extreme heat of reentry tarnish the bits of Mars that manage to reach us on their own, obscuring the subtleties of a world that, billions of years ago, resembled our own. For decades, scientists have explored the planet with rovers, orbiters, and landers, but these missions can carry only a few instruments at a time, and can’t match the equipment of the world’s best research facilities. A tiny piece of Mars in a lab, as pristine as it was on that distant rust-colored surface, is almost as good as being there.
The mission, as cutting-edge as it is, is reminiscent of an older way of doing science. In the age of Charles Darwin and Alexander von Humboldt, naturalists and other explorers traveled, welcome or not, to faraway places to gather trunkfuls of specimens for closer study. They sent their treasures back home on long sea journeys, during which hungry rats and pestilence were the most immediate dangers. Like those bygone voyages, modern efforts in space remain full of risk and unknowns. Sample missions unspool across many years and hundreds of thousands, or even millions, of miles, with potential technical tangles at every step. The Japanese mission that brought those asteroid samples to Australia a decade ago was riddled with glitches from start to finish. Transporting scientific treasures from continent to continent is no longer particularly difficult, but dispatching a robotic probe deep into space still means that years of work could come to nothing.
The first sample-return missions went to the moon. In the late 1960s and early ’70s, Apollo astronauts gathered more than 800 pounds of material from the lunar surface, guided by the wish lists of geologists back home and whatever happened to catch their eye. These were the first and last celestial samples collected by hand.
Spacecraft now do that work, but machine explorers require a bit more programming than human ones. The new Mars rover, named Perseverance, will use its robotic arms and other instruments to drill into the rock, scoop some pieces into test tubes, and seal them. Engineers have tested it countless times, and even included a cleaning mechanism meant to shake loose any Martian dust that gets stuck in the hardware’s crevices.
The capsules inside the Perseverance rover, 43 in total, are each about the size of a standard laboratory test tube. They are designed to protect samples from the Martian elements, and were cleaned meticulously, so that whatever comes back is “irrefutably Martian,” says Pavlina Karafillis, an engineer at NASA’s Jet Propulsion Laboratory who tested the tubes. To handle the capsules on Earth, Karafillis wore two layers of protective clothing, two pairs of gloves, and goggles. The biggest potential source of contamination is the people working on these capsules. “The contamination-control people sent out a list of approved hair products that were unscented, to make sure that, basically, the outgassing of our hair products didn’t impact the tubes at all,” Karafillis told me.
The canisters are good for at least 10 years. The Perseverance rover can hold on to them, carrying the precious materials within itself as it roams across Mars’s landscape. It can, with the help of its robotic arm, stack them in a pile on the surface, or stash them beneath a rock. They will be safe on the surface. The Martian wind is strong enough only to blanket the canisters in a layer of dust, not sweep them away. NASA, along with the European Space Agency, plans to build and dispatch more spacecraft in coming years to pick up the samples and launch them off Mars. Expected delivery: 2031.
The Mars samples will return to Earth the same way astronauts do—shrouded in a heat shield to protect them from burning up. They will fall to Earth and crash into a patch of Utah desert, in a capsule that must be designed to withstand the impact. In 2004, a NASA mission launched to collect solar particles accidentally landed so hard that it shattered, and recovery workers spent days picking through the desert for bits of hardware embedded with microscopic samples, which they miraculously managed to salvage. Like the Australian outback, the Utah desert is a good recovery spot; less water means fewer chances of losing your interplanetary treasure in a murky puddle. Thankfully there are no kangaroos, but officials must account for hidden, unexploded bombs lurking beneath the surface, left over from military tests in the area.
Once recovered, the samples will be delivered into the careful hands of experts trained to work with them. Each tube can hold less than an ounce of material, and although scientists are used to handling tiny specimens, the work can sometimes be exasperating. Samples the size of molecules “will sometimes move without you touching them,” says Eileen Stansbery, the head of NASA’s astromaterials-research division. Sneeze, and a precious particle is gone. “If you drop it, and you think you see it on the surface, are you sure that’s the right grain?" Zolensky said. “Maybe it’s something you dropped two years ago, and it’s still lying there.”
Even the smallest particles can tell important stories. A sample-return mission that flew through a comet’s tail in 2004 revealed in exquisite detail the composition of these objects. The Japanese missions to asteroids provided clues about how our solar system came to be. Some scientists have proposed flying a probe through the plumes of Enceladus, an icy moon of Saturn, to check whether its subsurface ocean contains any microbial life. The Perseverance rover is designed to search for signs of ancient, fossilized life forms. Could hints of that life end up in the tubes?
If the Mars samples survive a decade on the red planet—and reentry and potential lab mishaps— they will be studied for decades. In 2019, NASA curators dipped into the Apollo vault and brought out lunar samples that had remained untouched since they arrived in the early ’70s. Scientists had set them aside for future researchers equipped with better instruments. “The Apollo samples are still being studied with instrumentation that had not been invented yet when the samples were collected, by people not yet born, to answer questions not yet asked,” Jason Dworkin, a NASA scientist who works on the agency’s asteroid mission, told me.
The work of engineers and scientists on the Mars mission reminds me of the story of a 20-year-old music student who broke into a London museum in 2009 and stole hundreds of bird skins, many of them collected 150 years earlier by the naturalist Alfred Russel Wallace. To the young thief, the specimens were not precious scientific artifacts, but something he could sell in an unusual underground market for rare feathers used in fly-fishing lures. But to Wallace, the birds must have felt quite alien once, just as the Mars samples will to modern scientists. Someday, pristine pieces of our neighboring planet could be scattered across museums, as commonplace as taxidermied birds.