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- Bennu is a carbon-rich asteroid<\/strong> that passes semi-close to Earth about every six years. Scientists say it might have originated from a larger body farther out in the solar system.<\/li>\n
- Bennu contains a wide variety of molecules that are ingredients for life<\/strong>, at least on Earth. That\u2019s according to a new study of samples brought back to Earth in 2023. There\u2019s also evidence for salty liquid water on Bennu (and possibly on a parent world for Bennu) billions of years ago.<\/li>\n
- The conditions necessary for the emergence of life<\/strong> were widespread across the early solar system, the results suggest.<\/li>\n<\/ul>\n
New analysis of samples from asteroid Bennu<\/h3>\n
Scientists have completed a new detailed analysis of samples from asteroid Bennu, which were returned to Earth by the OSIRIS-REx spacecraft in late 2023. NASA reported on January 29, 2025, that the samples contain molecules that, at least on Earth, are the building blocks of life. <\/p>\n
Bennu contains all 5 of the nucleobases that form DNA and RNA on Earth. The asteroid also contains 14 of the 20 amino acids found in known earthly proteins. But \u2013 in a fundamental way \u2013 the chemical structure of the molecules in Bennu aren\u2019t like those on Earth. Earthly amino acids found in living organisms typically have a \u2018left-handed\u2019 chemical structure. Bennu appears to contain nearly equal amounts of \u2018left-handed\u2019 and their \u2018right-handed\u2019, or mirror-image, forms. What does it mean? Scientists aren\u2019t sure yet.<\/p>\n
And there\u2019s more. There\u2019s also evidence for saltwater brines that might once have existed on an original parent world of which Bennu was a part, billions of years ago. The findings show that conditions would have been ideal for these molecules to interact together in the briny \u201cbroth.\u201d This suggests that conditions for the emergence of life might have been widespread in the early solar system.<\/p>\n
The researchers, led by NASA and the Smithsonian, published their peer-reviewed results in two new papers in Nature Astronomy<\/em> and Nature<\/em> on January 29, 2025. You can read them here and here.<\/p>\n
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Not only does Bennu contain all 5 of the nucleobases that form DNA and RNA on Earth and 14 of the 20 amino acids found in known proteins, the asteroid\u2019s amino acids hold a surprise<\/p>\n
\u2014 Nature (@nature.com) 2025-01-29T16:38:16.890Z<\/p>\n<\/blockquote>\n
![\"Squarish](\"https:\/\/earthsky.org\/upl\/2021\/10\/asteroid-bennu-Dec2-2018-OSIRIS-REx-e1635250626903.jpg\")
The OSIRIS-REx spacecraft and its PolyCam instrument collected 12 images to make this mosaic of asteroid Bennu on December 2, 2018. The spacecraft was just 15 miles (24 km) from the asteroid. 2 new studies of samples brought back to Earth by OSIRIS-REx show that Bennu contains a treasure trove of the molecular building blocks of life. They also show that Bennu and its original parent world had salty (briny) water in which these molecules could have interacted and combined. While not proof of life itself, it means that the conditions existed for the possible eventual emergence of life, similar to the early Earth. Image via NASA\/ University of Arizona.
<\/figcaption><\/figure>\nBuilding blocks of life on asteroid Bennu<\/h3>\n
The first paper in Nature Astronomy<\/em> details the molecules discovered. The researchers found 14 of the 20 amino acids that life on Earth uses to make proteins. They also found all five nucleotide bases \u2013 nitrogen-containing biological compounds \u2013 that earthly life uses to store and transmit genetic instructions in more complex terrestrial biomolecules, such as DNA and RNA. This includes how to arrange amino acids into proteins, necessary for life as we know it.<\/p>\n
In addition, the scientists also discovered large amounts of ammonia, as well as the organic compound formaldehyde. Under the right conditions, they can react together to form amino acids. The amino acids can then form long chains to create proteins.<\/p>\n
These are all essential building blocks of life, at least life as we know it on Earth. It isn\u2019t proof<\/em> of life itself having existed on Bennu or its hypothetical parent world, but it does show that conditions were suitable for life to have emerged.<\/p>\n
![\"Black](\"https:\/\/earthsky.org\/upl\/2025\/01\/Na-carbonate-Bennu-Nature-January-29-2025.jpeg\")
View larger. Na carbonate, or sodium carbonate\/ trona, in the form of microscopic \u201cneedles\u201d in a sample from asteroid Bennu. Image via McCoy et al.\/ Nature (Open Access\/CC BY 4.0).<\/figcaption><\/figure>\n ![\"Man](\"https:\/\/earthsky.org\/upl\/2025\/01\/Bennu-sample-Goddard-Space-Flight-Center-January-29-2025.jpg\")
View larger. | Jason Dworkin at NASA\u2019s Goddard Space Flight Center holds up a vial that contains part of the sample from asteroid Bennu that NASA\u2019s OSIRIS-REx mission delivered to Earth in 2023. Image via NASA\/ James Tralie.<\/figcaption><\/figure>\n More questions<\/h3>\n
Amino acids can be either \u201cleft-handed\u201d or \u201cright-handed\u201d (meaning there are two different mirror-image versions of each amino acid). This is called chirality. The amino acids on Bennu are pretty much equally left-handed and right-handed. Does that mean that amino acids on the early Earth were both as well? And why does life on Earth now use the left-handed variety almost exclusively?<\/p>\n
Further study of the Bennu samples might help to solve such mysteries. What they do show already is that conditions suitable for the emergence of life were likely widespread through the entire early solar system. That increases the possibility of life having developed elsewhere, such as ocean moons like Europa and Enceladus.<\/p>\n
Jason Dworkin is the OSIRIS-REx project scientist at Goddard and co-lead author on the Nature Astronomy<\/em> paper. He summarized the mission, saying:<\/p>\n
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OSIRIS-REx has been a highly successful mission. Data from OSIRIS-REx adds major brushstrokes to a picture of a solar system teeming with the potential for life. Why we, so far, only see life on Earth and not elsewhere, that\u2019s the truly tantalizing question.<\/p>\n<\/blockquote>\n
A salty, watery environment<\/h3>\n
Meanwhile, the other research team focused on what the overall conditions were like on Bennu and its parent body billions of years ago. The molecules found by the first team are exciting, but what kind of environment did they exist in? Tim McCoy, curator of meteorites at the Smithsonian\u2019s National Museum of Natural History in Washington, led the study.<\/p>\n
The researchers found 11 minerals called evaporites \u2013 calcite, halite, sylvite and others \u2013 known to form when water containing dissolved salts evaporates over long periods of time. In other words, brines: very salty water. After the water evaporates, it leaves behind solid crystals.<\/p>\n
As with the other molecules, such evaporites have been seen in meteorites before. But the ones in Bennu are the first to provide a record of the entire evaporation process. And some of them had not been found before, such as trona, a water-bearing sodium carbonate (soda ash).<\/p>\n
These findings show that Bennu did have the molecular building blocks of life. But in addition, it also had an environment that could support the eventual emergence of life itself. The briny broth would be ideal for those molecules to interact and combine, much like what scientists think happened on the early Earth.<\/p>\n
Another study from last year also showed evidence for Bennu\u2019s original home \u2013 the larger rocky body that it broke off of \u2013 being a primitive ocean world.<\/p>\n
McCoy said:<\/p>\n
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These papers really go hand in hand in trying to explain how life\u2019s ingredients actually came together to make what we see on this aqueously altered asteroid.<\/p>\n<\/blockquote>\n
![\"Small](\"https:\/\/earthsky.org\/upl\/2025\/01\/Bennu-sample-Goddard-Visitor-Center-Michael-Maimone.jpeg\")
View larger. | Michael Maimone of EarthSky took this photo of a Bennu sample at the Goddard Visitor Center in Greenbelt, Maryland. Thank you, Michael!<\/figcaption><\/figure>\n Conditions for life widespread in early solar system<\/h3>\n
Scientists have found these kinds of building blocks and water before, in meteorites. But what makes these even more significant is that Bennu originally formed far from the sun in the outer solar system. The new findings support the idea that such building blocks of life \u2013 and suitable conditions for the emergence of life \u2013 were widespread throughout the early solar system. Bennu and other space rocks would have been an important source of the necessary molecules.<\/p>\n
And, importantly, these samples from Bennu are pristine and uncontaminated. Danny Glavin, a co-lead author on the second paper and a senior sample scientist at NASA\u2019s Goddard Space Flight Center in Greenbelt, Maryland, said:<\/p>\n
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The clues we\u2019re looking for are so minuscule and so easily destroyed. That\u2019s why some of these new discoveries would not be possible without a sample-return mission, meticulous contamination-control measures, and careful curation and storage of this precious material from Bennu.<\/p>\n<\/blockquote>\n
Nicky Fox, associate administrator, Science Mission Directorate at NASA Headquarters in Washington, added:<\/p>\n
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Asteroids provide a time capsule into our home planet\u2019s history, and Bennu\u2019s samples are pivotal in our understanding of what ingredients in our solar system existed before life started on Earth.<\/p>\n<\/blockquote>\n
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Remember when we brought pristine asteroid samples back to Earth? The first big science is in!<\/p>\n
The samples suggest that the early solar system had widespread conditions and ingredients for life. Here’s how we know: pic.twitter.com\/pwsDAXtY2J<\/a><\/p>\n
- Bennu contains a wide variety of molecules that are ingredients for life<\/strong>, at least on Earth. That\u2019s according to a new study of samples brought back to Earth in 2023. There\u2019s also evidence for salty liquid water on Bennu (and possibly on a parent world for Bennu) billions of years ago.<\/li>\n