A NASA spacecraft scooped rubble from an asteroid. Here's what was inside
OSIRIS-REx sample includes building blocks of proteins and DNA, evidence of water
Scientists have finally had a close look at the rubble collected by a NASA spacecraft from an asteroid. In it, they've found new clues about the ingredients for life that were present in the early solar system and how they might have come to Earth.
An international team of scientists has released some of their discoveries about the samples collected by the NASA spacecraft Osiris-REx from the near-Earth carbon-rich asteroid Bennu in 2020 and returned to Earth in 2023.
Bennu, a carbon-rich asteroid that orbits as close as 300,000 kilometres to Earth, was part of an ancestral asteroid that formed in the early solar system about 4.5 billion years ago. Because of that, it can tell scientists what molecules needed for life were present in the early solar system.
"This asteroid is like a frozen time capsule," said Kim Tait, senior curator of mineralogy at the Royal Ontario Museum in Toronto and co-author of a new study on its mineral composition.
What scientists found on the asteroid
By examining the minerals from the now dry and dusty asteroid, the researchers could tell that its parent asteroid once contained pockets or veins of salty water and that there was sodium, chlorides, fluorides, carbonates and phosphates in the salt, they reported Wednesday in Nature. The crystals seemed to form the way they do in salt lakes on Earth.
A separate analysis of molecules important to life found amino acids, including 14 of the 20 used to build proteins in living things. It also found all five nucleobases or building blocks of RNA and DNA, the researchers reported in Nature Astronomy.
At a NASA news conference Wednesday, Sara Russell, co-lead author of the mineral study , said the briny fluids would have been "crammed full" of elements necessary to life, such as phosphorus and sulphur, and some of the salts and clays could have catalyzed reactions to generate more complex molecules.
"We're finding this story where together the water, the organic materials and all of these bioessential elements could have been delivered on asteroids like Bennu in the early solar system to the Earth — and other planets as well — to enable them to be seeded with all the ingredients they needed to kick-start life," said Russell, research scientist at the Natural History Museum in London.
There was already evidence from meteorites and another asteroid sampling mission, the Japan Space Agency's Hayabusa2, that space rocks can carry water necessary for life and biological building blocks such as amino acids and nucleobases.
But Bennu's rubble also contained surprises.
Tait said it showed carbon-based molecules were forming in "very salty, briny water, which we didn't expect at all."
Tim McCoy, curator of meteorites at the Smithsonian's Natural Museum of Natural History and co-lead author of the new mineral study, told the news conference: "We've never seen minerals like this in meteorites before," even though meteorites are pieces of asteroids that have fallen to Earth.
He said even tiny amounts of water in the Earth's atmosphere can cause some salts to dissolve and disappear as a meteorite passes through it.
The new discoveries show how missions that take samples from space, return them to Earth and distribute them to be studied by scientists without exposure to things like water and oxygen are "absolutely essential," McCoy said.
Bennu crushes theory about origin of left-handed amino acids
One of the other questions related to the origin of life that scientists wanted to explore with this mission was why amino acids, which can come in chemical forms called "left-handed" and "right-handed," are only found in the left-handed form in living things.
"It's a big mystery. We don't know how this happened," Danny Glavin, lead author of the Nature Astronomy study, told the news conference.
Many meteorites similar to Bennu have had more of the left-handed form, leading scientists to suggest that there were more left-handed molecules in the early universe.
But the amino acids collected from Bennu are in both left-handed and right-handed forms in roughly equal amounts.
"I have to admit I was a little disillusioned or disappointed," said Glavin, senior scientist at NASA Goddard Space Flight Center. He said for now, the origin of left-handedness of amino acids on Earth "continues to remain a mystery."
The researchers wrote in the Nature study that the conditions that must have existed on the ancient asteroid that Bennu came from "pose an intriguing, but untested environment" for forming molecules necessary for life. They suggest conducting experiments to see whether the building blocks of DNA and RNA can form in similar chemical conditions in the lab.
"We now know we have the basic building blocks to move along this pathway towards life, but we don't know how far along that pathway this environment could allow things to progress," McCoy said.
Tait added that one of NASA's priorities is to look for water in space because it's necessary for life.
"I find that this gets me really excited," she said, "and I hope it gets other people really excited about the possibilities of other life out there."
While there are signs that places like the planet Mars might once have had water and a warmer climate, Gordon Osinski, a professor at Western University in London, Ont., said the new findings "might mean that ... even asteroids may have had the conditions suitable for life."
There's currently no water on Bennu, and the new study suggests it evaporated sometime in the past.
Tait was part of a working group of scientists who met biweekly to discuss and interpret the new results from analyses of different portions of the asteroid sample distributed to labs around the world.
Canada was part of the team for the asteroid return mission because it contributed an instrument used to map the asteroid in order to collect the sample.
Chris Herd, a professor and geologist at the University of Alberta, is expecting to get a Bennu sample soon for his team to study and is intrigued by the new results.
"I'm excited because it allows us to compare the asteroid that we've sampled with meteorites that are already in our collections," he said.
But Herd noted that the new studies show that a sample collected directly from an asteroid and kept under controlled conditions "will reveal more information" than meteorites exposed to Earth's warm temperatures and chemicals in its atmosphere.
Osinski agreed that the exciting thing about samples from Bennu is that they were collected in space. "And they're absolutely pristine.... So we know anything found in these samples came from and was formed either on this asteroid or out there in the solar system."
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