After seven years alone in space, NASA’s OSIRIS-REx spacecraft is speeding back toward Earth with a long-awaited delivery: a capsule containing about eight ounces of rock and dust from a nearby asteroid called Bennu.
The asteroid samples will plop to the ground in the Utah desert around 8:55 AM Mountain Daylight Time on Sunday morning. A helicopter will quickly swoop in and whisk the sample container away to a military clean room, like something out of a science-fiction movie (and you can watch the whole thing live on NASA TV). By next week, bits of the asteroid will be on their way to scientists around the world, who will study the material for clues about how water and organic chemicals arrived on Earth just in time to kickstart life as we know it.
But OSIRIS-REx won’t be coming home. By the time the Bennu asteroid samples hit the ground, the spacecraft will be long gone on its next errand, a 2029 rendezvous with another nearby asteroid called Apophis (a big favorite of both Egyptologists and Stargate: SG1 fans). The spacecraft will even get a spiffy new mission name: OSIRIS-APEX.
What is OSIRIS-REx? Where is Bennu, and why is it so important?
OSIRIS-REx, launched in 2016, is the first American mission to bring back samples of an asteroid. Japan has already done it twice, first bringing back a pinch of dust from Itakawa in 2010 and then about a teaspoon of material from Ryugu in 2020. But the eight ounces of dust and rock aboard OSIRIS-REx are the largest handful of asteroids anyone has managed to bring home so far — and they could be a treasure trove of information about the early Solar System and the delivery of water and other essential chemicals for life, to our planet.
Bennu is a carbon-rich asteroid, well stocked with organic compounds: Chemicals made of rings or chains of carbon atoms, usually also bound to hydrogen atoms. Organic compounds also often contain oxygen and nitrogen, along with other chemical elements. These chemicals are the building blocks of the building blocks (of the building blocks) of life.
During its mission, OSIRIS-REx also found evidence that there was once liquid water in one of the ancient asteroids that collided to form the pile of rocky debris that’s now Bennu. By studying the samples of Bennu that OSIRIS-REx is bringing home, scientists hope to learn more about how asteroids like Bennu may have brought their rich troves of water and organic compounds to Earth during a much earlier and more violent period in our Solar System’s history.
And Bennu itself is a product of that early violence; It’s what planetary scientists call a “rubble pile” asteroid; instead of a solid chunk of rock, Bennu is a floating pile of rocky chunks, loosely held together by their mutual gravity. Dimorphos, which was recently visited via the DART mission, is another rubble pile asteroid.
All of those things combine to make Bennu an interesting target for science, which is why OSIRIS-REx spent four years getting there and another two years bringing home souvenirs for hundreds of scientists around the world. The spacecraft launched in September 2016 (which NASA claims was actually just seven years ago, not several hundred, but we’re not convinced), gathered samples of rock and dust in 2020, and started for home in 2021. And now it’s almost here.
Who Gets a Piece of the OSIRIS-REx Asteroid Samples?
NASA will keep about 70 percent of the 8.8 ounces of material OSIRIS-REx is dropping off; some will be available “on request” to scientists and schools around the world. Of the rest, about 25 percent will be split among the 233 scientists on the official OSIRIS-REx science team, who come from 38 institutions in several different countries. Tinier amounts will go to the Canadian Space Agency and the Japan Aerospace Exploration Agency – 4 percent and 0.5 percent of the total, respectively.
What’s About to Happen with OSIRIS-REx?
In the wee hours of the morning U.S. Mountain Daylight Time on Sunday, when OSIRIS-REx is still about 63,000 miles away from Earth and coming in hot, the spacecraft will release the capsule full of asteroid bits. Four hours later, the sample capsule will slam into Earth’s atmosphere above the coast of California, moving at more than 27,000 miles per hour. Parachutes will start popping out a few minutes later, and by the time the capsule settles to Earth at 8:55 A.M MDT, it will be moving at a sedate 11 miles per hour, assuming everything goes according to plan.
The capsule’s target is a remote strip of Utah desert, 36 miles long and 8.5 miles wide, which belongs to the U.S. Department of Defense’s Utah Test and Training Range. Typically, the range plays host to weapons tests, military training exercises, and explosive ordnance disposal, but OSIRIS-REx isn’t the range’s first space rodeo. Samples of comet dust from NASA’s Stardust mission landed here in 2006, and samples of cosmic wind particles from the Genesis mission had a bit of a rough landing here in 2004.
To hit that relatively small target, the whole process has to be choreographed almost perfectly. OSIRIS-REx fired its thrusters on September 10 to change its speed by just half a mile per hour — a tiny but crucial adjustment, without which the spaceship would just go whizzing past Earth too far away to drop off its package.
The spacecraft was still 4 million miles away at the time but closing fast. A week — and 2.2 million miles — later, on September 17, another tiny adjustment changed OSIRIS-REx’s speed (relative to Earth) by just 7 inches a minute. That nudged the spaceship’s landing site about eight miles east, aiming it right at its landing strip in Utah.
Once the sample capsule touches down, a crew will pick it up and fly it to a clean room elsewhere on the base, where other crews will prepare it for a flight to NASA’s Johnson Space Center on Monday (NASA rehearsed this process on August 30, as pictured above). From there, bits of the samples will go all over the world.
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