UPDATE: Oct. 20, 2020, 6:41 p.m. EDT: The story below has been updated to reflect that NASA successfully touched the surface of Bennu to collect samples.
Asteroid Bennu has had its close-up.
On Tuesday, at around 6:12 pm, NASA’s OSIRIS-REx spacecraft took a tiny piece of Bennu to return to Earth, a process that took just 16 seconds. (You can watch a recording of the event here.) Mission development started over a decade ago, and it’s already been four years since the spacecraft launched. Even though the sample is safe in the spacecraft, it won’t return to Earth until 2023.
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Why go through all this trouble to sample a space rock that's more than 200 million miles away from Earth? It turns out that despite their humble appearances, asteroids have a lot to offer scientists.
“They are like time capsules from the beginning of our solar system,” said Richard Binzel, an astronomer at the Massachusetts Institute of Technology and one of the scientists working on the OSIRIS-REx mission. In the 4.5 billion years that the solar system has been around, asteroids like Bennu have stayed largely the same.
“This is like sampling the original ingredients for making planets,” said Binzel.
The OSIRIS-REx mission goes all the way back to 2004, when the mission’s principal investigator Dante Lauretta, a planetary scientist at the University of Arizona, first proposed a version of the mission as part of NASA's Discovery Program. Carried out by NASA and aerospace company Lockheed Martin, its name stands for different elements of the mission. The “O” stands for “origins” — the origins of the solar system and even the planet. Asteroids like Bennu could have collided in the early solar system to form planets like ours.
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Bennu also may hold the key of another origin — the potential origins of the ingredients of life. Some scientists think that some of the carbon on Earth could have come from an outside source, like an asteroid. Bennu appears “black as coal,” said Jason Dworkin, the mission’s project scientist at the Goddard Space Flight Center, which means that the asteroid is rich in carbon, said Dworkin. It’s what’s called a carbonaceous asteroid. And carbon is crucial to the development of life.
Binzel says that it is hotly debated among scientists whether ingredients for life could really have come from an asteroid like Bennu. But it’s possible.
“If you ask 100 scientists, you'll probably get 120 different answers,” he said. Nevertheless, Bennu is definitely rich in carbon, a fact already confirmed by equipment onboard the spacecraft. Binzel led the development of this instrument, which was built by a team of MIT and Harvard students and analyzes x-ray radiation coming off of Bennu’s surface. Analyzing how much different elements of the surface “glow” with x-ray radiation can identify what the surface is made of.
Another reason scientists are so keen to get this sample from an asteroid is that carbonaceous asteroids are fragile. Scientists have had plenty of chances to study asteroids from Earth in the form of meteorites. But they tend to break up in the atmosphere, and even if they don’t, they don’t survive their descent to Earth unscathed.
“Once the meteorite lands on Earth, it starts getting altered by the atmosphere,” said Thomas Burbine, an astronomer who directs the astronomical observatory at Mount Holyoke College. A sample fresh from an asteroid avoids this fate, allowing scientists to study its unaltered chemistry.
Bennu isn’t just a carbonaceous asteroid, but one that is surprisingly close-by. These asteroids are usually far-flung, orbiting the sun in the outer edges of the asteroid belt between Mars and Jupiter. But Bennu happens to be closer — well within range to study. That also presents a potential problem. Because Bennu is close to us, there is a small chance it could hit the Earth in the future.
“We’re talking about a very low probability,” said Binzel. Still, Dworkin emphasized that part of the purpose of the mission is to try to understand how to manage the hazard of a potential asteroid collision with the Earth. In fact, the second “S” in “OSIRIS-REx” stands for “security.” Scientists want to understand the feasibility of measures like redirecting asteroids, and to do that, they need to know what the asteroids are made of.
“It mattered to the dinosaurs,” said Binzel, “and we’d like to be smarter than the dinosaurs.”
Of course, learning exactly what Bennu is made of will have to wait until 2023, when the sample will finally make its way to Earth and eventually to Dworkin’s lab at Goddard. But scientists have already learned a lot from OSIRIS-REx.
“Bennu is a rocky, craggy surface,” said Dworkin, which scientists didn’t expect at all. They thought it would be relatively smooth and sandy with few notable features. But Bennu is covered in loose boulders, which added an extra challenge when trying to decide where to land the spacecraft.
Another crucial part of the mission is resource identification — the "RI" in OSIRIS-REx. Bennu seems to have quite a bit of water on it, bound up with minerals in the form of ice. In the future, Dworkin says, it’s possible people will use asteroids for their resources, water in Bennu’s case, a concept often referred to as “asteroid mining.”
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“You might have a market for water directly in space,” said Martin Elvis, an astrophysicist at the Smithsonian Astrophysical Observatory. He thinks that in a decade, we could be extracting resources from asteroids, especially for use on longer voyages in space. Elvis says that water could also potentially be used as rocket fuel, either injected at a high speed to drive a spacecraft or broken down into its component parts of oxygen and hydrogen gas.
Other scientists are skeptical. “I don’t think in the near future we’re going to have any asteroid mining,” said Burbine. It would be extremely expensive, he said, and the tiny sample that OSIRIS-REx is working so hard to get would hardly be worth anything, either for water or metal.
Nevertheless, the knowledge gained from this mission to Bennu could influence the way we use resources, the way we think about our solar system’s origins, and our understanding of how life evolved. And that understanding doesn’t stop with OSIRIS-REx. A mission to a metallic asteroid called Psyche is set to launch in August 2022, while Lucy, a mission that will explore some of the asteroids near Jupiter, has an even sooner October 2021 launch date. Two Japanese missions, Hayabusa and Hayabusa2, have also already sampled asteroids — Hayabusa2 will return with its sample in December. NASA’s DART mission will look further into the practicalities of redirecting asteroids.
“This is like the golden age of asteroid study,” said Burbine.
UPDATE: Oct. 21, 2020, 11:05 a.m. EDT This article has been corrected to reflect that Martin Elvis is an astrophysicist at the Smithsonian Astrophysical Observatory, not Harvard University and the Smithsonian Institute as was previously stated.
