Unprecedented asteroid samples contain organic compounds and minerals crucial to life, scientists say

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29-01-2025

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Researchers have detected organic compounds and minerals necessary for life in unprecedented samples collected from the near-Earth asteroid Bennu, adding evidence to the idea that asteroids likely delivered the building blocks of life to our planet early in its history.
The samples are also providing a window into understanding what kind of chemical and biological processes were already underway as space rocks chaotically ricocheted around during the early days of the solar system.
Preliminary analyses of the rock and dust samples released within the past year have shown that the asteroid contained water as well as carbon, nitrogen and other organic matter, but the chemical composition of the organic material was largely unknown.
Now, new research has revealed the asteroid contains many of the chemical building blocks of life, such as amino acids and components found in DNA, said Dr. Daniel P. Glavin, senior scientist for samples return at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
'This is all very exciting because it suggests that asteroids like Bennu once acted like giant chemical factories in space and could have also delivered the raw ingredients for life to Earth and other bodies in our solar system,' said Glavin, lead author of a study on the samples published Wednesday in the journal Nature Astronomy.
Additionally, the authors of a separate paper published Wednesday in the journal Nature uncovered salts and minerals crucial to life, including some never seen in asteroid samples before, within Bennu's rocks — as well as highlighting the role that ancient water played on the asteroid.
The results of both papers, shared Wednesday during a NASA press conference, present a 'groundbreaking scientific discovery,' said Nicky Fox, associate administrator for NASA's Science Mission Directorate.
'These two papers together go hand in hand to say that Bennu was a much more interesting and complicated place than we probably gave it credit for even six months ago,' said Dr. Tim McCoy, co-lead author of the Nature study and curator of meteorites at the Smithsonian's National Museum of Natural History.
Bennu is a carbon-rich space rock known as a rubble pile asteroid. Scientists believe Bennu was once part of a larger 'parent' asteroid that lost a few pieces due to an impact. Then, those blasted-off pieces coalesced, like a pile of rocky rubble that is weakly held together by gravity.
The sample was collected from Bennu in October 2020 by a NASA mission called OSIRIS-REx, or Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer. It marked the first time the US sent a spacecraft to briefly land on an asteroid and collect material. The OSIRIS-REx spacecraft then dropped off a capsule when it swung by Earth in September 2023, sending it parachuting down into the Utah desert.
A team of researchers worked to carefully retrieve the capsule and ensure that the samples inside remained pristine and completely sealed against any of Earth's atmosphere and environment that could contaminate the extraterrestrial rocks and dust and potentially skew any analysis of its properties.
Scientists were thrilled when they realized that the capsule contained double the expected cache of material, which amounted to about 120 grams, or about the weight of a bar of soap. Samples were divided up and shared with researchers around the globe.
Glavin and his team detected thousands of organic molecular compounds, including 33 amino acids, in the Bennu samples they studied. Amino acids, or molecules that combine to form proteins, are some of the building blocks of life.
The researchers found 14 of the 20 amino acids that are used in biology to build proteins, and 19 non-protein amino acids, many of which are rare or nonexistent in known biology, Glavin said.
The team also detected adenine, guanine, cytosine, thymine and uracil — all five of the biological nucleobases, or components that make up the genetic code in DNA and RNA.
'These organic molecules have all been found previously in meteorites, but in contrast to meteorites, the Bennu samples are pristine and were protected from heating during atmospheric entry and exposure to terrestrial contamination,' Glavin said. 'So we have a much higher confidence now that these chemical building blocks of life are in fact extraterrestrial in origin and formed in space, and are not contaminants from Earth.'
Glavin's team also found compounds rich in nitrogen and ammonia in the samples, suggesting that Bennu was part of a larger asteroid that formed about 4.5 billion years ago in the frigid, distant regions of the solar system. Ammonia is essential for many biological processes, Glavin said.
Ammonia ice is more stable the farther it is from a heat source, like the sun. The researchers believe that the ammonia-enriched ice melted inside the large parent asteroid body, estimated to be bigger than 62 miles (100 kilometers) in diameter, creating a liquid environment inside the rock that allowed complex organic molecules, such as the amino acids and nucleobases, to form.
'Having studied meteorites for 35 years, these record the first half billion years of our solar system history that were wiped out by plate tectonics and volcanism and the water cycle here on Earth,' McCoy said. 'I thought we were going to learn about the earliest geologic history of our solar system. What we ended up finding was a lot of information about the earliest biologic history of our solar system, which is remarkable.'
McCoy's team, including 66 researchers across four continents, found the salt and minerals left behind as water on Bennu, or its larger parent asteroid, evaporated. The minerals include sodium phosphates, carbonates, sulfates, chlorides and fluorides, some of which are necessary to the formation of life.
The team was surprised to find the mineral trona, also known as sodium carbonate or soda ash, which has never been directly observed in another asteroid or meteorite. On Earth, it is used in cleaning products and glass manufacturing.
The researchers believe that pockets or veins of water flowed beneath the surface of Bennu's parent asteroid, which was probably similar to a big ball of mud in the early days of the solar system, McCoy said. Cracks and fractures in the asteroid allowed water to evaporate to the surface, leaving behind a concentrated brine, or a 'soup of the elements,' in its wake.
This concentrated brine, similar to the salty crusts of dry lakebeds on Earth, is where salts and minerals could mingle and create more complex structures, setting the stage for organic compounds to form.
'We now know from Bennu that the raw ingredients of life were combining in really interesting and complex ways on Bennu's parent body,' McCoy said. 'We have discovered that next step on a pathway to life. But we don't know how far along that pathway this environment could allow things to progress.'
Brines are of interest to planetary scientists because they could be environments that support the formation of life. It's also possible that they exist on other worlds in our solar system, including ocean worlds such as Saturn's icy moon Enceladus — which also contains sodium carbonate.
The presence of water, minerals, salts and amino acids suggests it was possible for the building blocks of life to come together in interesting ways on Bennu, but Glavin said more research is required to determine how organic compounds formed and evolved on the space rock.
Many of the minerals have small bits of water trapped in their crystalline structures, so researchers may be able to learn about how the composition of the brine changed over time, which could provide clarity about what took place in the evaporating water, McCoy said.
One of the mysteries presented by the samples is a mixture of amino acids.
Amino acids have handedness, meaning they can be created in two mirror-image versions, like a pair of hands. On Earth, life produces left-handed amino acids, so Glavin expected to see that reflected in the Bennu samples — but it contains an equal mixture of both, suggesting that amino acids likely began on Earth as both. Now, Glavin and his colleagues wonder why life on Earth 'turned left' rather than right.
The combination of material found in the samples suggests chemical building blocks of life were widespread throughout the solar system, providing strong evidence that the asteroids bombarding early Earth may have delivered water and organic material to its surface, Glavin noted.
But that theory raises the question of whether this life-delivering bombardment ever successfully occurred on any other planet in the solar system, McCoy said. And there is also the puzzle of why life didn't form inside Bennu itself, given that most of the raw ingredients needed were present, Glavin said.
'Maybe it was because there just wasn't enough time to do the more complex organic chemistry need for life before the salty liquids evaporated in the parent body,' Glavin said. 'Future missions to other bodies in our solar system will be critical to seek the answers about how life began on Earth and our search for life elsewhere.'