DNA building blocks found in asteroids for first time
The building blocks of DNA have been found in samples returned to Earth from an asteroid, suggesting life rained down from space and could have formed elsewhere.
In 2016, Nasa sent its Osiris-Rex mission to drill down into the asteroid Bennu, with the cargo returning to Earth in 2023.
The first analysis shows that the four nucleotide bases of DNA – adenine, guanine, cytosine and thymine – which form the rungs of the double helix, were all present.
Every living thing on Earth contains DNA, which stores the genetic information needed to build and maintain an organism.
It is the first time that all four nucleotide bases have been discovered together on an asteroid, and the samples were also found to contain 14 of the 20 amino acids that life on Earth uses to make proteins.
The findings from the sample increase the likelihood that the conditions for life were widespread across the early solar system – Yasuhiro Oba
Nasa said the findings not only suggest that space rocks sparked life on Earth, but that the conditions for life were widespread across the early solar system.
Nicky Fox, the associate administrator for the Nasa Science Mission Directorate, said: “Bennu contains many precursor building blocks of life along with the evidence it comes from an ancient wet world.
“The findings do not show evidence for life itself, but they do show that the conditions necessary for the emergence of life were likely widespread across the early solar system. This of course increases the odds that life could have formed on other planets.
“This all supports the theory that Bennu [was] among the sources that delivered water and chemical building blocks for life to Earth.”
Minerals found in samples from Bennu formed when saltwater evaporated in extraterrestrial ponds – Rob Wardell, Tim Gooding and Tim McCoy, Smithsonian
Scientists also discovered 11 important minerals, including sodium, carbon, sulphur and phosphorus, which were left behind when saltwater streams evaporated.
Researchers believe these extraterrestrial sub-surface ponds may have provided a cauldron where the elemental ingredients for life could intermingle and create more complex molecules.
Similar conditions are thought to exist on Ceres – a dwarf planet in the asteroid belt between Mars and Jupiter – which suggests it would be a good place to look for the existence of life.
Scientists collect data next to the return capsule from Osiris-Rex, which brought back asteroid samples that are often difficult to study – Keegan Barber/Nasa
Sara Russell, a cosmic mineralogist at the Natural History Museum in London, who studied the material, said: “There were things in the samples that completely blew us away. The richness of the molecules and minerals preserved are unlike any extraterrestrial samples studied before.
“It’s interesting that although Bennu had everything needed for life – it did not form.
“The complex and delicate conditions needed to catalyse life really bring into focus the abundance of biodiversity here on Earth.”
She added: “Together we have made huge progress in understanding how asteroids like Bennu evolved, and how they may have helped make the Earth habitable.”
A sample of Bennu shown inside the Osiris-Rex sample collector, which brought back about four ounces (113g) of material from the asteroid – Nasa Handout/AFP
Bennu is more than four-and-a-half billion years old and is a relic from the formation of the solar system which has been perfectly preserved in the vacuum of space.
It is about 1,640ft (500m) across and once belonged to a much larger asteroid which broke apart billions of years ago.
Scientists have long suspected that the ingredients for life on Earth were delivered to our planet by asteroids, but they are tricky to study once on the ground because they are easily contaminated.
Tim McCoy, curator of meteorites at the Smithsonian’s Museum of Natural History, says Bennu is ‘the next step on a pathway to life’ – James Di Loreto/National Museum of Natural History (NMNH), Smithsonian Institution
The Osiris-Rex mission collected around four ounces (113g) of rock and dust from Bennu – about the weight of a bar of soap – and the samples were divided up and sent to laboratories around the world for study.
Among the new findings were some more familiar minerals such as halite, which is made of sodium chloride and is more commonly called rock salt.
Tim McCoy, the curator of meteorites at the Smithsonian’s Museum of Natural History, in Washington DC, added: “We now know from Bennu that the raw ingredients of life were combining in really interesting and complex ways.
“We have discovered the next step on a pathway to life. 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.”
The research was published in the journal Nature Astronomy.
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