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Organic molecules have been detected in samples collected by Japan’s Hayabusa2 mission from the near-Earth asteroid Ryugu.
“When researchers analyzed the samples, collected from two different locations on the asteroid, they found uracil, one of the building blocks of RNA, as well as vitamin B3, or niacin (a key cofactor for metabolism in living organisms).
Uracil is a nucleobase, or a nitrogen-containing compound. It’s one of five nucleobases in DNA and RNA, the proteins and molecules that contain genetic information and instructions crucial for the cells of living organisms.
A study detailing the findings published Tuesday in the journal Nature Communications.
Ryugu is a carbon-rich, diamond-shaped asteroid that measures about 3,000 feet (1 kilometer) wide. Hayabusa2 was the first mission to return a subsurface sample from an asteroid to Earth.
The Japanese Aerospace Exploration Agency mission collected one sample from the asteroid’s surface in February 2019, then fired a copper “bullet” into the asteroid to create a 33-foot (10-meter) wide impact crater. A sample was collected from this crater in July 2019. Then, Hayabusa2 flew by Earth and dropped the sample off in Australia in December 2020.
In earlier analyses, researchers detected amino acids and other molecules in Ryugu’s samples, while uracil and niacin have also been found in meteorites that landed on Earth.
“Scientists have previously found nucleobases and vitamins in certain carbon-rich meteorites, but there was always the question of contamination by exposure to the Earth’s environment,” said lead study author Yasuhiro Oba, associate professor at Hokkaido University in Japan, in a statement. “Since the Hayabusa2 spacecraft collected two samples directly from asteroid Ryugu and delivered them to Earth in sealed capsules, contamination can be ruled out.”
Building blocks of life in space
The researchers discovered the molecules when they soaked particles collected from Ryugu in hot water and analyzed the results using different observational methods, such as liquid chromatography and mass spectrometry.
Then, the team detected the signatures of uracil, niacin and other organic compounds containing nitrogen.
“Other biological molecules were found in the sample as well, including a selection of amino acids, amines and carboxylic acids, which are found in proteins and metabolism, respectively,” Oba said.
Together, the findings from Ryugu’s samples so far add to the increasing evidence that the building blocks of life originated in space and were originally delivered to Earth billions of years ago by meteorites.
The molecules likely originally formed through photochemical reactions in ice in outer space before our solar system even existed, Oba said.
Further study of asteroid composition
The concentrations of the molecules in the two samples were different, but that’s likely due to exposure to the harsh environment of space. It’s possible that Ryugu was once part of a larger celestial body, like a comet, before it was broken apart into pieces by collisions with other space objects.
“It is no doubt that biologically important molecules such as amino acids and nucleobase(s) in asteroids/meteorites have been provided to the Earth,” Oba said. “In particular, we expect they might play a role for prebiotic evolution on the early Earth.”
It’s also possible that as space rocks smashed into other planets in our solar system, they might have been carrying some of the same building blocks of life.
“I cannot say the presence of such ingredients directly leads to the emergence/presence of extraterrestrial life, but at least their components such as amino acids and nucleobases may be present everywhere in space,” Oba said.
Now, the researchers want to know how common these molecules are in asteroids. Fortunately, a sample from another asteroid named Bennu will be delivered to Earth in September by NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, or OSIRIS-REx spacecraft.
“The discovery of uracil in the samples from Ryugu lends strength to current theories regarding the source of nucleobases in the early Earth,” Oba said. “The OSIRIS-REx mission by NASA will be returning samples from asteroid Bennu this year, and a comparative study of the composition of these asteroids will provide further data to build on these theories.”