The Japanese probe Hayabusa2 collected in 2018 about 5 grams of material from the Ryugu asteroid, a 900-meter-diameter ‘spinning top’ 280 million km from Earth, and brought them to our planet two years later. Since then, the remains (basically black dust and rocks) have been studied by a large number of scientific teams, who have been publishing their own conclusions about the composition and origin of this object even older than the Sun.
The last of them, published this Tuesday in the journal ‘Nature Communications’, suggests that the asteroid contains nitrogenous organic compounds, including uracil, a nucleotide that is part of RNA. According to the researchers, this is one more example that the basic elements for life on Earth could have come from space in meteorites.
Uracil is one of the information units that make up RNA, the molecules that contain the instructions for how to build and operate living organisms. Nicotinic acid, also known as vitamin B 3 or niacin, important for the metabolism of living organisms, was also detected in the same samples.
“Scientists have previously found nucleobases and vitamins in certain carbon-rich meteorites, but there has always been the question of contamination from exposure to Earth’s environment,” explains Yasuhiro Oba of Hokkaido University and leader of the international team that led out the study. “Since the Hayabusa2 spacecraft collected two samples directly from the Ryugu asteroid and delivered them to Earth in sealed capsules, contamination can be ruled out,” he stresses.
The researchers extracted these molecules by immersing the Ryugu particles in hot water, followed by analysis using liquid chromatography along with high-resolution mass spectrometry. This revealed the presence of uracil and nicotinic acid, as well as other nitrogen-containing organic compounds.
Proteins and metabolism
“We found uracil in the samples in small amounts, in the range of 6 to 32 parts per billion (ppb), while vitamin B 3 was more abundant, in the range of 49 to 99 ppb,” says Oba. Other biological molecules were also found in the sample, “including a selection of amino acids, amines, and carboxylic acids, which are found in protein and metabolism, respectively.” The detected compounds are similar but not identical to those previously discovered in carbon-rich meteorites.
The team hypothesizes that the difference in concentrations in the two samples, collected at different locations on Ryugu, is likely due to exposure to the extreme environments of space. They also hypothesized that nitrogen-containing compounds formed, at least in part, from simpler molecules such as ammonia, formaldehyde, and hydrogen cyanide. While these were not detected in the Ryugu samples, they are known to be present in cometary ice, and Ryugu could have originated as a comet or another main body that was present in low-temperature environments.
“The discovery of uracil in the Ryugu samples gives strength to current theories about the origin of nucleobases on the early Earth,” concludes Oba. “NASA’s OSIRIS-REx mission will return samples of asteroid Bennu this year, and a comparative study of the composition of these asteroids will provide more data to develop these theories,” he adds.