NASA is about to grab its first glimpse of an asteroid. On October 20, some 334 million kilometers from Earth, the agency̵
The journey to Bennu’s surface won’t be easy. The spacecraft will have to cross a towering boulder nicknamed Mount Doom, then over a sampling area no larger than a few parking spaces. “We may not be successful on our first try,” says Dante Lauretta, the mission’s principal researcher and planetary scientist at the University of Arizona in Tucson. But if it works, he says, “I hope the world sees this as good news, something we can be proud of with all the craziness that’s going on this year.”
There and back again
Launched in 2016, the $ 800 million OSIRIS-REx is NASA’s first asteroid sampling mission. It follows two missions from the Japanese Aerospace Exploration Agency (JAXA) that collected dust from the surface of asteroids, including some recovered last year that are currently on their way back to Earth for analysis. Prior to JAXA’s missions, scientists learned about the contents of asteroids mainly by studying meteorites that have fallen to Earth and these can be contaminated as they travel through the atmosphere and hit the planet.
Digging a sample directly from an asteroid offers a pristine look at the rocks left behind by the formation of the Solar System more than 4.5 billion years ago. Each asteroid has its own story to tell about how it formed and evolved over time; Bennu is particularly tempting because it may contain material rich in organic compounds found throughout the Solar System, including life on Earth.
But first OSIRIS-REx will have to do the sampling. When Lauretta and her colleagues chose Bennu as their target, they thought the 500-meter-wide asteroid would be relatively smooth and easy to land. But after OSIRIS-REx arrived and started orbiting Bennu in 2018, the aircraft took a closer look and found large dangerous boulders.1.
So the mission engineers developed an automated system to guide the spacecraft to the surface. It collects images as the spacecraft descends and compares them to previously taken images of the same target region. OSIRIS-REx can then monitor whether it is safe on the pre-selected path. If not, it can abort itself and fly away from the asteroid, waiting for a second chance to descend.
Its target is a 16m wide crater called Nightingale, which offers a relatively smooth surface for a landing. If you could stand in the middle of the nightingale, you would feel pebbles and fine-grained sand beneath your feet, says Erica Jawin, a planetary scientist at the Smithsonian National Museum of Natural History in Washington DC, who studied Bennu’s geology.2. Mount Doom would loom overhead, roughly the height of a two-story building, which is “pretty intimidating,” he says.
OSIRIS-REx will descend towards Nightingale with its 3.3 meter long robotic arm outstretched. When it touches the asteroid, a feat expected at 6:12 pm. Eastern time in the United States, it will release a puff of nitrogen that will blow across the surface, raising small specks in a cloud of asteroid debris. A sampling device will collect some of these particles and store them.
The process, which will only last 10-15 seconds, is more of a “punch blow” than a landing. As soon as the spacecraft finishes vacuuming, it will return to a safe distance and scientists will evaluate the amount of material collected. NASA wants at least 60 grams of rocks and dust, but closing will be good enough. “If it’s 58 grams, we’re putting away and going home,” says Lauretta.
If the spacecraft picks up 40 grams or less, scientists are likely to return it to a second location on Bennu, called Osprey, to pick up more. (He can’t go in to sample Nightingale a second time, because the original nitrogen blast will have pushed small rocks to the surface in uncertain places, making a “ double dip, ” dangerous, says Lauretta.) January; Regardless, the spacecraft is expected to depart Bennu in March and will eventually land on Earth with its precious cargo in 2023.
Anatomy of asteroids
Bennu has been through a lot in his life. It formed between about 100 million years and a billion years ago when it broke away from a larger “parent” body during a cosmic collision in the Solar System’s asteroid belt. But Bennu kept the traces of his parent. While orbiting the asteroid, OSIRIS-REx found that some of the boulders on Bennu are traversed by veins of ancient carbon-rich material known as carbonate. The carbonate probably formed when the ice melted and dripped through the parent body, causing aqueous reactions within its rocks.
“I was surprised” to see these veins, says Hannah Kaplan, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of Science paper3 who announced the discovery. They measure centimeters in width and can stretch more than a meter, much larger than the carbonate veins seen in some meteorites. According to Lauretta, the large veins suggest that Bennu’s parent body once had a huge system of hot water flowing through it, meaning it had a lot of active geology. Some fragments of these carbonates may lie on the ground in Nightingale and be collected by OSIRIS-REx.
The researchers plan to compare Bennu’s samples with those currently on their way back to Earth from Ryugu, the largest asteroid that JAXA’s Hayabusa2 probe visited last year. “I feel like a spoiled child cutting two delicious cakes on my birthday,” says Queenie Hoi Shan Chan, a planetary scientist at Royal Holloway, University of London, Egham, UK, who works on Hayabusa2. Ryugu appears to have less water-rich material on its surface than Bennu; By comparing the samples, researchers will be able to better understand how common aqueous processes and organic materials are on asteroids, says Chan.
Scientists will also scour the Bennu rocks for clues on how to protect Earth from asteroids. Bennu orbits dangerously close to Earth and has a small chance of crashing into the planet in the 22nd century. Studies have shown that the asteroid is more of a loosely piled pile of rubble than solid rock. By closely examining the texture of Bennu rocks, scientists could propose ways to deflect or break up threatening near-Earth asteroids.
“Any sample of Bennu will be incredibly useful, a vital addition to the collection of planetary samples we have on Earth,” says Jawin. “It probably won’t matter too much if we were there and stole some of his rocks.”