\ud83c\udf18Subscribe to 404 Media to get The Abstract, our newsletter about the most exciting and mind-boggling science news and studies of the week. Scientists have discovered all five nucleobases\u2014the fundamental components of DNA and RNA\u2014in pristine samples from the asteroid Ryugu, according to a study published on Monday in Nature Astronomy. The finding strengthens the case that the ingredients for life are abundant in the solar system and may have found their way to Earth from space, according to a study published on Monday in Nature Astronomy.\u00a0Life as we know it runs on DNA and RNA, which are built from five chemical bases: adenine, guanine, cytosine, thymine, and uracil. A team has now identified this \u201ccomplete set\u201d of nucleobases in rocks snatched from the surface of Ryugu in 2019 by the Japanese spacecraft Hayabusa-2, which successfully returned them to Earth the following year.This discovery corroborates the results from another mission, NASA\u2019s OSIRIS-REx, which returned samples of the asteroid Bennu that also contained all five nucleobases. Both asteroids belong to the same \u201ccarbonaceous\u201d (C-type) family of primitive carbon-rich rocks, though the samples contain different ratios of the five nucleobases.\u00a0Taken together, the findings shed light on the origin of life on Earth and raise new questions about the odds that it exists elsewhere.\u00a0\u201cThese findings suggest that nucleobases may be widespread in carbonaceous asteroids and, by extension, in planetary systems,\u201d said Toshiki Koga, a postdoctoral researcher at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), in an email to 404 Media.\u00a0\u201cThis means that some of the key molecular ingredients for life could be commonly available,\u201d he added. \u201cHowever, this does not imply that life itself is widespread, but rather that the chemical starting materials for life may be more common than previously thought.\u201dThe emergence of life on Earth, also known as abiogenesis, remains one of the biggest mysteries in science. To untangle this enigma, scientists first need to figure out how our planet was initially enriched with the basic stuff of life\u2014including water, amino acids, and the nucleobases that make up our genetic material.The \u201cRyugu Story\u201d illustration depicting the detection of all five canonical nucleobases in samples returned from asteroid Ryugu by the Hayabusa2 mission. Image: JAMSTEC\u00a0One popular hypothesis suggests that asteroids bearing these biological building blocks pelted Earth as it formed more than four billion years ago. This idea has been supported by the presence of nucleobases in pieces of carbonaceous asteroids that have fallen down to Earth, such as the Murchison meteorite of Australia or the Orgueil meteorite of France.\u00a0Meteorites, however, are not pristine as they become eroded by exposure to space and can also be contaminated by terrestrial material after landing on Earth. To get cleaner samples, scientists launched several spacecraft to grab samples directly from the source, beginning with Japan\u2019s Hayabusa mission, which delivered several milligrams of dusty grains from asteroid Itokawa to Earth in 2010.\u00a0Hayabusa-2 and OSIRIS-REx then obtained even larger samples from their targets, bringing back 5.4 grams from Ryugu and 121.6 grams from Bennu. Previous studies have already identified more than a dozen amino acids associated with life in both samples, as well as evidence that these asteroids were once altered by ice and water.\u00a0Now, following the discovery of all five nucleobases in the Bennu pebbles, Koga and his colleagues have found the complete set in Ryugu. The findings lend weight to the so-called \u201cRNA world\u201d model of abiogenesis. In this hypothesis, early life on Earth depended solely on RNA as a self-replicating molecule, laying the biological groundwork for later, more complicated systems that involved DNA and protein-based organisms. The extraterrestrial samples from Ryugu and Bennu provide evidence that at least some of the nucleobases that made up these early lifeforms came from outer space.The results were \u201cbroadly in line with our expectations, but still very exciting to confirm,\u201d Koga said. \u201cAll five nucleobases had already been detected in the Murchison meteorite and in samples from the asteroid Bennu. Since Ryugu is also a carbonaceous asteroid, we expected that these molecules might be present, and it was very satisfying to confirm that the complete set is indeed present in the Ryugu samples.\u201dBut while both samples contained the royal flush of nucleobases, they differed in their relative abundances. For example, Bennu is much richer in pyrimidine nucleobases (cytosine, thymine and uracil) than Ryugu, though they both contain roughly similar levels of purine nucleobases (adenine and guanine). These idiosyncrasies point to a variety of formation processes that produced prebiotic materials on these celestial relics.\u201cOur results suggest that nucleobases can form under a range of conditions in early Solar System materials, particularly within primitive asteroid parent bodies that experienced aqueous alteration,\u201d Koga said. \u201cThe observed relationship between nucleobase composition and ammonia abundance indicates that local chemical environments, such as the availability of ammonia, may play an important role.\u201d\u00a0\u201cAt the same time, some precursor molecules may have formed earlier in interstellar environments, so nucleobase formation could involve multiple stages,\u201d he continued. \u201cFuture studies, including analyses of different types of meteorites and laboratory experiments that simulate these conditions, will help to better constrain these formation pathways.\u201dIn other words, understanding how these molecules form in space could help answer the age-old mystery of whether life is a rare cosmic fluke\u2014or a common process in the universe. The research also highlights the remarkable ingenuity behind these sample-return missions, which have delivered tiny time capsules from the birth of our solar system directly into our hands.\u201cIt is both exciting and humbling to work with these samples,\u201d Koga said. \u201cThey are extremely limited and represent material that has remained largely unchanged since the early Solar System. At the same time, there is a strong sense of responsibility, because each tiny grain may contain important information about how organic molecules formed and evolved before the origin of life.\u201d\ud83c\udf18Subscribe to 404 Media to get The Abstract, our newsletter about the most exciting and mind-boggling science news and studies of the week. <\/p>\n","protected":false},"excerpt":{"rendered":"