NASA’s OSIRIS-REx spacecraft just won one of the most epic games of tag in human history. Last month, the plucky little craft reached out and high-fived Bennu, a diamond-shaped asteroid roughly the size of a skyscraper, snatching a sample of its surface in the process.
Orbiting the hunk of rock more than 200 million miles from Earth, the spacecraft extended its robotic arm and blasted the asteroid’s surface with pure nitrogen gas. It then used a sample collection head to vacuum up the disturbed material.
But OSIRIS-Rex’s collection head may have worked too well. It snagged so much rocky material that it couldn’t close its collection flap securely. Precious rocks leaked out into space, creating a dilemma about how the spacecraft should go about storing its cargo.
“This is the mission that keeps on surprising us,” said Dante Lauretta, University of Arizona planetary scientist and principal investigator of the OSIRIS-REx mission during a news conference three days after the collection. “We could not have performed a better collection experiment: It was successful, we collected 100s of grams of samples, but the biggest concern is that particles are escaping.”
Images and video beamed back from the spacecraft showed that its collection head contained a hefty stash of asteroid rubble, including some fairly larger pieces of rock. Lauretta said these bulkier pebbles were just large enough to prevent that flap from closing. This discovery forced the mission team to completely change its plans. Instead of taking the time to measure how much sample was collected, the team had to race to store the rocks before too much was lost to space—a meticulous process that took several days to complete.
Scientists say the touch and go maneuver resulted not only in a successful sample collection but also provided new information about the layer of loose rocks that may cover the surfaces of many small planetary bodies, like asteroid Bennu. The material, previously thought to be akin to solid bedrock, is actually more like a playground ball pit.
The team is anxious to get their hands on the sample, but won’t know for sure exactly how much material they have until the craft returns to Earth in three years. But scientists are very confident that they grabbed more than the minimum mission requirement of 60 grams. Based on images beamed back, Lauretta and his team think they’ve grabbed at least 400 grams of material.
Despite the uncertainty, OSIRIS-REx did something that no other NASA spacecraft has done: reach out and touch the surface of an asteroid. This daring maneuver has been decades in the making.
NASA scientists started planning the mission in 2004. Four years ago, OSIRIS-REx launched on its journey to Bennu. OSIRIS-REx, which is short for Origins Spectral Interpretation Resource Identification Security and Regolith Explorer, is designed to answer a number of fundamental questions including "Where did we come from?" Asteroids are scientific treasure troves because they contain pieces of the earliest materials that formed our solar system. Moons and planets change over time, but most asteroids do not, which makes them perfectly preserved galactic fossils. “They can provide valuable information about how planets, like our own, came to be,” said Lori Glaze, NASA’s director of planetary science, in a news briefing.
Earth has an atmosphere and active plate tectonics. As a result, its oldest rocks are typically weathered or are pushed deep into the mantle. So, researchers often use pieces of asteroids that land here—called meteorites—to learn more about the composition of the solar system and ancient Earth.
Asteroids can contain carbon and other organic compounds, including the building blocks of life, not found on meteorites. To really understand how life on Earth started billions of years ago, scientists say we need to go somewhere where no life exists yet—like Bennu.
OSIRIS-REx arrived at Bennu in 2018 and began its orbit, spending nearly two years extensively mapping the asteroid using a laser altimeter, a device that uses laser beams to measure the surface of planets and other rocky bodies. Based on preliminary data, Lauretta and his team expected to see a sandy surface, but were shocked to find Bennu was covered in boulders. This presented a challenge, as the team originally planned to land the craft on the asteroid and collect samples. Since Bennu is essentially a floating cosmic rubble pile, the team decided to forego a landing, and instead decided on an approach using that robotic arm.
Regolith, the dirt and rubble found on an asteroid, is just like the dirt found on Earth, but in outer space, traditional means of scooping and digging it up won’t work thanks to the lack of gravity. Engineers at Lockheed Martin in Colorado, where the spacecraft was built, needed to figure out how to collect the sample. Jim Harris, a Lockheed engineer, helped come up with the idea of vacuuming up regolith. Using a solo cup and an air compressor in his driveway, he tested out a very rudimentary prototype.
Originally dubbed Muucav (vacuum spelled backwards), a refined version of Harris’ contraption was built and called the Touch And Go Sample Acquisition Mechanism, aka TAGSAM. The device consists of that robotic arm and a vacuum that looks like a giant, round showerhead. But instead of water shooting out, the head blasts Bennu’s surface with gas, sucks up material and stores it. TAGSAM, which was loaded with three containers of gas, had three chances to collect a minimum of 60 grams (2 oz) of asteroid. The collection capsule far exceeded that on the first try, which the scientists deducted when they saw the collection head couldn’t close.
Originally, the team had planned to measure how much rock was in the sample head by commanding the spacecraft to spin around in place with its robotic arm extended. The more collected material, the more force it would take to speed up OSIRIS-REx’s rotation, allowing researchers to estimate the amount of sample to within a few grams. Since the flap couldn’t close, the team wanted to minimize the amount of sample lost to space, so they chose to skip the measurement step and focus on stowing the sample head as soon as possible.
The team very carefully moved the sample head—open flap and all—to a storage container and gingerly placed it inside. Two locking mechanisms secured it. The arm then gently tugged on the head to make sure it was set.
OSIRIS-REx will stay in orbit around Bennu until March, when it will depart the asteroid. The return trip to Earth will take approximately two-and-a-half years. At that point, the sample collection canister will separate from the spacecraft and parachute down, landing in the Utah desert in September 2023. It could be carrying the largest extraterrestrial sample since the Apollo era.
Researchers around the world are already prepping their labs to study this material. One reason Bennu was selected as a target is because scientists believe it’s a fragment of what was once a much larger space rock. As a body that broke off during a collision between two asteroids early in our solar system’s history, the 4.5 billion-year-old rubble pile is a perfectly preserved cosmic time capsule.
In a series of papers published in the journal Science on October 8, Lauretta and a team of researchers discovered that Bennu contained a cosmic prize: thick veins of organic minerals called carbonates, which form in hydrothermal systems. The collected samples could help scientists better understand the role asteroids played in bringing water and prebiotic material to Earth, providing the building blocks for life.
Jamie Elsila, a research scientist at NASA Goddard Space Flight Center, is especially interested in amino acids—which form proteins—that evolved within Bennu’s dirt. Life on Earth uses 20 amino acids, but many more have been identified within meteorite samples that have fallen to the ground. Those samples could have been affected by their trip through the atmosphere. Bennu’s samples are pristine, which means they could help scientists pinpoint which amino acids were present in the early solar system—and deduct how they may have influenced life on Earth.
Studying bits of Bennu could also have broader implications for life throughout the universe. “If this kind of chemistry is happening in the early solar system, it probably happened in other solar systems as well,” Lauretta says. “It could help us assess the likelihood of life throughout the galaxy and, ultimately, the universe.”