Confirming the existence of RNA nucleobases in space rocks, a recent study of an asteroid sample extracted from Ryugu has revealed the presence of uracil, one of the four building blocks of RNA. The study also identified niacin, a form of vitamin B3, that plays a significant role in metabolism, in the dust that was brought back to Earth from the asteroid.
The discovery of RNA nucleobases in an asteroid sample adds to the growing evidence that the components of life are formed in space, and suggests that asteroid impacts may have delivered these building blocks to Earth in its early history.
Although scientists had previously identified nucleobases and vitamins in carbon-rich meteorites, contamination from Earth’s environment was a concern. However, the use of sealed capsules to collect two samples directly from asteroid Ryugu by the Hayabusa2 spacecraft rules out this possibility, according to astrochemist Yasuhiro Oba from Hokkaido University in Japan. Understanding the emergence of life and its prevalence in the Milky Way galaxy remains an intriguing question for humanity.
One approach is to search for the components of life in space and investigate potential mechanisms for their transportation to Earth.
Increasingly, it appears that the elements that make up life are abundant in space. Evidence of these building blocks has been discovered in planet-forming dust, the clouds of star-forming dust that enshroud the center of our galaxy, and in meteorites that have made their way to Earth.
The accumulation of these findings supports the idea that life’s components may have an extraterrestrial origin. However, there was still uncertainty about this idea until scientists could eliminate the possibility of contamination from Earth material.
In order to analyze the pristine samples collected by the Hayabusa2 spacecraft from asteroid Ryugu, Yasuhiro Oba and his colleagues developed a new method to detect and identify nucleobases in tiny quantities.
To analyze the two samples collected from asteroid Ryugu, the team subjected them to a process that involved soaking them in hot water and utilizing high-performance liquid chromatography in combination with electrospray ionization high-resolution mass spectrometry. In a previous experiment using the Murchison meteorite that fell to Earth in 1969, this technique had resulted in the detection of all five canonical nucleobases.
The range of biomolecules found in Ryugu was smaller, but still significant, the researchers believe.
“We found uracil in the samples in small amounts, in the range of 6–32 parts per billion (ppb), while vitamin B3 was more abundant, in the range of 49–99 ppb,” Oba says. “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.”
In addition to the roughly 20 amino acids that had already been identified in samples from Ryugu, the team also detected other compounds that are similar to those found in other carbon-rich meteorites that have impacted Earth. While these newly identified compounds are distinct from those found in other meteorites, they share some broad similarities. These findings imply that biomolecules may be abundant in carbonaceous meteorites and could have been transported to Earth during periods of heavy bombardment.