Time travel happens every day in a round-about way. Pieces of the past fall to the Earth in the form of meteors. Comets deliver particles from the early solar system as they blaze by the sun. Our air and soil carry radioactive traces of atoms from before our planet existed. Though eons of history come at us from every direction, these days, we also go to it, seeking out the future.
To pave the way for asteroid mining missions and more, NASA’s OSIRIS-REx spacecraft — short for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer — traveled for 755 days. Gaining speed as it slung around Earth before heading into deep space, O-REx, as it’s called in some circles, sailed up to the carbon-rich asteroid Bennu in December 2018.
Visiting the Bennu Asteroid
Bennu is one of 1.09 million known asteroids. Asteroids, in the aggregate, are hypothesized to be pieces of the primordial solar system that missed being swept into larger structures, such as a planet, moon or ring system. Individually, they contain varying amounts of water, metals and organic materials: all of which are original to the spinning disk that gave rise to every body ever explored by spacecraft, and all of which would be critical to building a future space settlement.
O-REx isn’t the first robotic explorer to go in search of pristine samples from billions of years ago. Using aerogel wands to capture particles from the tail of Wild 2, the comet-chasing Stardust spacecraft mission brought back around a milligram of material. In February 2019, JAXA mission Hayabusa 2 fired an explosive charge at asteroid Ryugu. The resulting robot-made crater provided our first glimpse of freshly exposed asteroid material. Hayabusa 2 then dropped micro-rovers onto Ryugu’s surface. In the low gravity, the three rovers that successfully landed hopped from place to place, taking photographs and temperature readings.
At only 500 meters (1,640 feet) in diameter, Bennu is the smallest object that humankind has ever orbited. To boot, O-REx orbited just 1.6 kilometers (1 mile) over Bennu asteroid’s surface — closer than any spacecraft has orbited any object in the history of space exploration to date. There was a method to this space-rock-buzzing madness. Though O-REx didn’t bring rovers or bombs, it had a few tricks up its mechanical sleeve that required close proximity.
In addition to three cameras and a laser altimeter for judging distance from the asteroid, O-REx had both an infrared and an X-ray scanner to measure material type and abundance. Close scans meant better readings. Better readings meant finding the best possible place to land.
Wait, land? Yes, land!
Dropping from touchdown distance to kissing distance was a requirement to put O-REx’s robotic arm into action. The touch-and-go sample acquisition mechanism (TAGSAM) was designed to basically fist-bump Bennu, then pinch off a little piece of the 4.5 billion-year-old asteroid. TAGSAM then passed the prize to its partner in crime, the OSIRIS-REx Sample Return Capsule (SRC). If all goes well, the SRC will return the 60 grams (2 ounces) of ancient material to Earth using parachutes plus the same kind of heat used by the highly successful Stardust, the Mars Science Laboratory and Mars 2020 missions.
Though the sample from OSIRIS-REx spacecraft could be measured in a few tablespoons (English or metric), analyzing it will help scientists understand the early solar system and the solar system to come. Depending upon what they contain — perhaps platinum for wires or water for plants — asteroids like Bennu could feed not only future space habitats but also the growing demand for materials that are rare on Earth or toxic to mine locally. Building Mars colonies and a better home world may mean cleaning some asteroids out of the solar system, or at least depositing them in the cosmic recycler.
Answering Questions We Haven’t Asked Yet
Studying the sample O-REx returns from Bennu will also equip us to better handle the hazards in our corner of space. While humankind makes plans to pursue knowledge, resources and wealth among asteroids both near and far, an unknown number of asteroids are headed in our general direction. Every year, a few of them slip past Earth’s planetary defense monitoring system — some because they are small, others because they are dark. Sometimes we see them coming from a distance, as we did with 2006 QV89, an asteroid half the size of a U.S. football field, which cruised smoothly into Earth’s orbital path and out again in 2020. The question of what to do with one that won’t leave so politely remains chillingly unanswered.
But O-REx may bring us closer to that answer. In addition to flying low, analyzing composition and sampling, part of its mission is to study the Yarkovsky effect: how much an asteroid moves when it absorbs light from the sun, then radiates that energy back into space. The effect is named for the 18th-century Russian engineer. His observation was that, due to the sun’s energy striking its surface, an asteroid’s course should alter over time. How the Yarkovsky effect manifests with Bennu — which could weigh as little as a cow or as much as a car — may help to propel planetary protection to a whole new level.
Well on its way to leveling up our space game, OSIRIS-REx headed home on May 26, 2021. The sample it carries, due to land sometime in September 2023, is destined for a bit of time traveling of its own. Astrobiologist Jason Dworkin from the Goddard Space Flight Center at NASA said 75% of the material returned by this mission will be “archived for future generations.”
Dworkin’s colleague Dr. Scott Sandford told NASA that he thinks these samples “will be studied by people not yet born, using techniques not yet invented, to answer questions not yet asked.” Much like the material brought back from the Moon and the asteroids found on ice sheets of Antarctica, the samples gathered by OSIRIS-REx will be teaching us about our place in the solar system for decades to come.
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