A NASA spacecraft, if all goes well, will soon touch down briefly on a skyscraper-sized asteroid 200 million miles away, in order to collect a small amount of rock and dust that can then be returned to Earth.
The probe, called OSIRIS-REx, is about as big as a 15-passenger van, and it needs to land for just 5 to 10 seconds on specific spot inside a boulder-strewn crater. The maneuver on Tuesday will be tricky and fraught with peril, as the spacecraft tries to reach a safe area that's only the size of a few parking spaces.
"It's up to fate and to a little bit of luck at this point as to how the sampling event goes," says Dante Lauretta of the University of Arizona, the principal investigator for the mission. He says he feels anxious but does yoga to calm his nerves. "I'm highly confident that the spacecraft will remain safe. My biggest concern is that it will not make it down to the surface of the asteroid."
The spinning top-shaped asteroid, named Bennu, is one of close to a million known asteroids in our solar system. Scientists want to study it in part to improve our planetary defenses against potentially dangerous space rocks. Bennu, for example, has a small chance of someday striking Earth.
"Our most recent calculations suggest that it has about a one in 2,700 chance," says Lauretta. "The good news is such an impact would not occur for at least 150 years, and part of the OSIRIS-REx mission is to better understand that impact probability."
Scientists also want to study asteroids like this one because they're thought to be nearly pristine time capsules—left-over bits from the early solar system that have gone undisturbed for billions of years.
"Asteroids are relics of the earliest material that formed the planets," says Lori Glaze, director of NASA's planetary science division. "They hold key information to unlocking our understanding of how the solar system formed and how it evolved."
This will be NASA's first attempt to collect a sample from an asteroid and bring it back to Earth, but others have tried it before. Japan's space agency has a spacecraft that's currently on the way home with a small amount of material taken from the asteroid Ryugu; it should arrive in December.
"There are some key differences," says Lauretta. He explains that NASA's rock collection equipment can hold onto a larger sample. While Japan's probe might bring home just tens of milligrams of material, OSIRIS-REx is capable of collecting up to two kilograms, or almost four and a half pounds.
OSIRIS-REX launched in 2016 and has been orbiting the asteroid since 2018. As soon as it arrived there, scientists got a close-up look at this space object and realized that Bennu was nothing like they thought. They'd expected the surface to be relatively smooth and covered with fine-grained material like sand. Instead, they saw boulders everywhere.
"When I first saw the rugged surface of asteroid Bennu, I knew we were in for a real challenge," says Lauretta.
The team spent a year mapping the asteroid in exquisite detail, finally settling on two craters where it looked possible to touch down: a primary target named Nightingale and back-up site named Osprey.
The spacecraft did low flybys to get high resolution imagery, in order to build 3-D maps that can used by its onboard navigation system. In April and August, the probe did two rehearsals, dipping down as close as about 130 feet above the asteroid's surface.
The first real attempt to collect rock and dust will happen in Nightingale, with the spacecraft departing from orbit around 1:50 p.m. EDT on Tuesday; the trip to the surface should take about four and a half hours and is full of hazards.
One rock, the size of a two-story building, looms over the edge of the Nightingale crater and is "reverently referred to as Mount Doom by members of our team," says Mike Moreau, OSIRIS-REx deputy project manager at NASA's Goddard Space Flight Center.
Because of the coronavirus pandemic, only a skeleton crew will be at the spacecraft's operations center at the Lockheed Martin Space Systems Facility in Littleton, Colorado, to monitor the probe's progress.
And they'll only be observers during the event. "In fact, by the time we get the data, everything that happened was 18 and a half minutes in the past because that's how far away the spacecraft is from the Earth," explains Lauretta.
"We don't have enough bandwidth to get imagery from the spacecraft as it's approaching the asteroid surface," he adds, explaining that they'll only get "breadcrumbs" of information from the probe's autonomous guidance system.
It's the last moments that will be the most nail-biting, he says, as the spacecraft compares what it sees to its onboard hazard map and decides whether it's safe to continue down to the asteroid surface. If the spacecraft thinks it's likely to hit some big rock, it will wave off the attempt.
But if it proceeds down to the surface, "the contact time is the real moment of terror for me. We know it's possible that the spacecraft could tip over and lose communication with the Earth. I'm really not looking forward to the moment of contact and the potential for loss of signal," says Lauretta. "The moment of relief is when we hear the spacecraft has fired its rocket engines and begun backing away from the asteroid surface."
The sample collector is at the end of an 11-foot-long arm and looks "a bit like an air filter you might see in an older car," says Sandra Freund, OSIRIS-REx mission operations manager at Lockheed Martin Space. It will actually take some time for researchers to assess how much dust and rock the collector managed to ingest.
The team should have enough information by October 30, however, to determine whether it's an acceptable amount to bring home or whether to go for an additional sampling attempt in January.
Eventually, whatever gets collected will be stowed in a secure return capsule, and the spacecraft will depart for Earth in March of 2021. Once it reaches our planet in September of 2023, it will release the sample return capsule, which will parachute down to Utah.
For Lauretta, who has worked on this mission for 16 years, it feels almost as if the spacecraft is part of the team. "We talk to it on a daily basis. It's kind of our eyes and our sensors, out deep in the solar system," he says. "We're going out there to retrieve this scientific treasure and bring it back to the Earth."
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