NASA is poised to make history next month.
The OSIRIS-REx probe is scheduled to pull off NASA's first-ever asteroid-sampling operation on Oct. 20, snagging precious dirt and gravel from a 1,640-foot-wide (500 meters) space rock called Bennu.
"I can't tell you how excited I am," OSIRIS-REx principal investigator Dante Lauretta, of the University of Arizona, said during a news conference on Thursday (Sept. 24). "I'm confident that we're up to the challenge that's ahead of us."
That challenge is considerable. OSIRIS-REx, which has been orbiting Bennu for nearly two years, will spiral down toward a small crater dubbed Nightingale on Oct. 20, aiming for a relatively flat, boulder-free region just 26 feet (8 m) wide. That will be a pretty tight squeeze for the spacecraft, which is the size of a 15-passenger van.
"This spot is just the width of a few parking places and is surrounded by large, boulder-like structures the size of small buildings," said Mike Moreau, OSIRIS-REx deputy project manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland. (The OSIRIS-REx team has nicknamed the most perilous of those obstacles "Mt. Doom," by the way.)
"So, for some perspective: The next time you park your car in front of your house or in front of a coffee shop and walk inside, think about the challenge of navigating OSIRIS-REx into one of these spots from 200 million miles away," Moreau said.
And OSIRIS-REx must make this bold move on its own. It will take signals more than 18 minutes to travel from Earth to the spacecraft on Oct. 20, far too long for real-time control.
The safe-touchdown zone is far smaller than the one originally envisioned by the mission team, which designed OSIRIS-REx with a 165-foot-wide (50 m) cushion in mind. But Bennu proved to be far more bouldery than observations by ground-based scopes had suggested. And the best sampling material — fresh and fine-grained stuff that hasn't been exposed to the harsh space environment for long — happened to reside in Nightingale.
OSIRIS-REx won't stay parked there for long. The probe will kiss the fine-grained dirt with its sampling mechanism, which is affixed to the end of an 11-foot-long (3.4 m) robotic arm, for just a few seconds. That dirt will be stirred up by a blast of nitrogen gas and collected by the sampling head, which team members have likened to a car air filter.
OSIRIS-REx will then back slowly and carefully away from Bennu, and the mission team will assess its catch. The goal is to get at least 2 ounces (60 grams) of asteroid material. If the Oct. 20 haul is deemed insufficient — and the team expects to decide one way or another on Oct. 30 — OSIRIS-REx could make another attempt, at a backup site called Osprey, no earlier than January 2021. (The probe has three nitrogen bottles, so it could theoretically take three swings at sample collection.)
If all goes according to plan, OSIRIS-REx will depart Bennu in March 2021 and head back toward Earth with its cosmic cargo. The asteroid sample will land in the Utah desert, encased in a special return capsule, on Sept. 24, 2023.
The material will then be studied by scientists around the world who want to learn about the solar system's early days and how life got started on Earth, among other topics. After all, asteroids are "time capsules" left over from the planet-formation epoch, NASA officials have stressed.
And Bennu is rich in carbon-containing organic compounds and hydrated minerals. It's therefore similar to the space rocks that many researchers think helped, via countless impacts, make Earth a habitable world long ago.
The $800 million OSIRIS-REx mission — whose name is short for "Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer" — launched in September 2016 and arrived in orbit around Bennu on Dec. 31, 2018.
The probe's work over the past 21 months hasn't been entirely devoted to prepping for the sample-collecting kiss. For example, its observations are also helping scientists better understand how asteroids move through space, which could lead to better trajectory forecasting for potentially hazardous asteroids (a class that includes Bennu).
OSIRIS-REx won't be the first probe to bring pristine asteroid bits down to Earth. Japan's Hayabusa probe delivered a few grains of the stony asteroid Itokawa in 2010. And the Hayabusa2 spacecraft recently collected samples of the carbon-rich asteroid Ryugu, which are scheduled to arrive here this December.
The OSIRIS-REx and Hayabusa2 teams have been working together over the years, and their collaboration will continue after both missions' samples come home, Lauretta said.
"Combined, it's an amazing data set — to be able to have information from these two near-Earth asteroids, which superficially look similar to each other but in detail are actually quite distinct," Lauretta said. "We're really excited to have an international coordinated sample-analysis program looking at both of the materials from these asteroids, and learning a lot more about asteroids in general and these carbon-rich asteroids in particular."
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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Michael Wall is a Senior Space Writer with Space.com and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.