Two organic compounds essential for living organisms have been found in samples retrieved from the asteroid Ryugu, buttressing the notion that some ingredients crucial for the advent of life arrived on Earth aboard rocks from space billions of years ago.
Scientists said on Tuesday they detected uracil and niacin in rocks obtained by Japan's space agency JAXA's Hayabusa2 spacecraft from two sites on Ryugu in 2019. Uracil is one of the chemical building blocks for RNA, a molecule carrying directions for building and operating living organisms. Niacin, also called vitamin B3 or nicotinic acid, is vital for their metabolism.
The Ryugu samples, which looked like dark gray rubble, were transported 250 million kilometers back to Earth and returned to our planet's surface in a sealed capsule that landed in 2020 in Australia's remote outback for analysis in Japan.
Scientists have long pondered on the conditions necessary for life to arise after Earth formed about 4.5 billion years ago. The new findings fit well with the hypothesis that bodies like comets, asteroids and meteorites that bombarded early Earth seeded the young planet with compounds that helped pave the way for the first microbes.
Scientists previously detected key organic molecules in carbon-rich meteorites found on Earth. But there was the question of whether these space rocks had been contaminated by exposure to the Earth's environment after landing.
"Our key finding is that uracil and niacin, both of which are of biological significance, are indeed present in extraterrestrial environments and they may have been provided to the early Earth as a component of asteroids and meteorites. We suspect they had a role in prebiotic evolution on Earth and possibly for the emergence of first life," said astrochemist Yasuhiro Oba from Hokkaido University in Japan, lead author of the research published in the journal Nature Communications.
RNA, short for ribonucleic acid, would not be possible without uracil. RNA, a molecule present in all living cells, is vital in coding, regulation and activity of genes.
Niacin is important in underpinning metabolism and can help produce the "energy" that powers living organisms.
The researchers extracted uracil, niacin and some other organic compounds in the Ryugu samples by soaking the material in hot water and then performing analyses such as liquid chromatography and high-resolution mass spectrometry.
Yoshinori Takano, a scientist at the Japan Agency for Marine-Earth Science and Technology and author of the Ryugu research, said he was also keenly awaiting the Martian Moons eXploration project that is set to launch from Japan next year and return around 2029.
It will collect samples from Phobos, one of the moons of Mars.
"I am sure it will be very hotly watched by organic cosmochemists for the next 10 years," Takano said.
“Since every meteorite has landed on the surface of the Earth where microorganisms are ubiquitously present everywhere, it always makes the interpretation on the origin of such biologically important molecules in meteorites more complex,” said Yasuhiro Oba, associate professor at Hokkaido University and an author of the research.
‘Like brewing coffee’
Testing the Ryugu samples was a multi-phase process that began by putting them in hot water, like “brewing coffee or tea”, Oba said.
Acid was then applied to extract molecules that were analysed by extremely sensitive tools capable of detecting the minute quantities of uracil present.
The discovery offers “strong evidence that one of the RNA components has been provided to the Earth even before the emergence of life”, Oba said.
“We expect it plays a role for prebiotic evolution and possibly the emergence of the first life,” he said. RNA’s other bases were not found in the sample, though Oba believes they could be present at levels too low to be detected with the method used to find uracil.
He hopes to analyse new samples collected from space in coming years, including Osiris-REx’s material from the asteroid Bennu, expected to arrive this year.
Yoshinori Takano, a scientist at the Japan Agency for Marine-Earth Science and Technology and author of the Ryugu research, said he was also keenly awaiting the Martian Moons exploration project, set to launch from Japan next year and return around 2029.
Agencies via Xinhua
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