NASA is about to capture the world̵7;s first taste of an asteroid. On October 20, about 334 million kilometers from Earth, the OSIRIS-REx spacecraft will approach a dark diamond-shaped asteroid named Bennu to touch its surface for a few seconds – long enough to cover the dust and pebble collection. If successful, the spacecraft will send this carbon-rich rubble back to Earth, where scientists will be able to explore it for clues to the history of the solar system.
The journey to the surface of Benn will not be easy. The spacecraft will have to make its way past a high boulder nicknamed Mount Doom, and then to a sampling area that does not exceed a few parking spaces. “We may not succeed on the first try,” said Dante Lauretta, the mission’s chief investigator and planetary scientist at the University of Arizona in Tucson. But if it still works, he says, “I hope the world looks at it as good news – something we can be proud of with all the insanity that’s happening this year.”
Back and forth
OSIRIS-REx, released in 2016 – $ 800 million – is NASA’s first sampling mission. This shows the two missions of the Japan Aerospace Exploration Agency (JAXA), which scooped dust from the surface of asteroids, including some obtained last year, which are now returning to Earth for analysis. Prior to the JAXA missions, scientists learned about the contents of asteroids, mainly by studying meteorites that fell to Earth – and they can be polluted when they travel through the atmosphere and hit the planet.
Extracting the sample directly from the asteroid provides an intact view of the rocks left over from the formation of the solar system more than 4.5 billion years ago. Each asteroid has its own story to tell how it formed and evolved over time; Bennu is particularly attractive because it may contain material rich in organic compounds contained in the solar system, including life on Earth.
But first OSIRIS-REx will have to take a sample. When Lauretta and his colleagues chose Benna as their target, they thought the 500-meter-wide asteroid would be relatively smooth and easy to land. But after OSIRIS-REx arrived and launched Benn’s orbit in 2018, the ship looked more closely and found large dangerous boulders1.
So mission engineers have developed an automated system to guide the spacecraft to the surface. It collects images when the spacecraft descends and compares them with previously taken images of the same target area. OSIRIS-REx can then monitor whether it is safe on its pre-selected path. If not, it can autonomously interrupt and fly away from the asteroid, waiting for a second chance to descend.
Its target is a 16-meter-wide crater named Nightingale, which offers a relatively smooth surface for landing. If you could stand in the middle of Nightingale, you would feel pebbles and fine sand underfoot, says Erica Javin, a planetary scientist at the Smithsonian’s National Museum of Natural History in Washington, D.C., who studied Benn’s geology.2. Mount Doom would hang over you, about the height of a two-story house, which is “pretty scary,” she says.
OSIRIS-REx will descend to Nightingale with an outstretched hand-arm 3.3 meters long. When he touches an asteroid, a feat scheduled for 6:12 p.m. Eastern time, he will release a gasp of nitrogen that will blow to the surface, knocking down small grains in a cloud of asteroid debris. The sampling device will cover some of these particles and store them.
The process, which takes only 10-15 seconds, is a “punch” rather than a landing. As soon as the spacecraft finishes the hoover, it will retreat to a safe distance, and scientists will estimate how much material it has collected. NASA wants at least 60 grams of rock and dust – but close will be pretty good. “If it’s 58 grams, we add it up and go home,” says Loretta.
If the spacecraft collects 40 grams or less, then scientists are likely to return it to the second place on Benna, called Osprey, to capture more. (He can’t take the Nightingale sample a second time, because the original nitrogen agent will push small rocks to the surface in uncertain places, making a “double dive” dangerous.) Osprey sampling is likely to take place in January; regardless, the spacecraft is scheduled to take off from Benn in March and 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 ago and a billion years ago, when it broke away from a larger “parent” body during a cosmic collision in the asteroid belt of the solar system. But Bennu left traces of his father. During the orbit of the asteroid OSIRIS-REx found that some boulders on Benna were pierced by the veins of an ancient carbon-rich material known as carbonate. Carbonate is probably formed when ice melts and flows through the mother’s body, causing watery reactions inside its rocks.
“I was surprised to see these veins,” said Hannah Kaplan, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author. Science paper3 which announced the discovery. They measure centimeters in width and can stretch to a length of more than a meter – much larger than the carbonate veins observed in some meteorites. According to Lauretta, the large veins indicate that Benn’s father’s body once had a massive system of hot water – which means that it had a lot of active geology. Some fragments of these carbonates may lie on the ground in Nightingale and be selected by OSIRIS-REx.
Researchers plan to compare Bennu’s samples with those now returning to Earth from Ryuga, a larger asteroid that visited JAXA’s Hayabusa2 spacecraft last year. “I feel like a spoiled child who cuts two delicious cakes for his birthday,” says Quinny Hoi Shan Chan, a planetary scientist from Royal Holloway, University of London, in Egham, UK, who works at Hayabusa2. Ryuga seems 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, Chan said.
Scientists will also study the rocks of Bennu to find clues on how to protect the Earth from asteroids. Bennu spins dangerously close to Earth and has little chance of crashing into the planet in the twenty-second century. Studies have shown that the asteroid is a more loosely accumulated rubble than a hard rock. By carefully studying the consistency of the Bennu rocks, scientists could suggest ways to deflect or split threatening near-Earth asteroids.
“Any sample from Benn will be extremely useful – an important addition to collecting samples of the planets we have on Earth,” says Javin. “It probably won’t worry too much that we were there and stole some rocks.”