The presence of RNA nucleobases in space debris has been verified by a
sample taken from an asteroid far from Earth.
Uracil, one of the four nucleobases that make up RNA, has been discovered
in dust brought home from the asteroid Ryugu, along with niacin, a type of
vitamin B3 that is crucial for digestion.This supports an increasing body of
data suggesting that the components for life exist in space and may have
been brought to Earth in part by an early asteroid impact.
Astrochemist
Yasuhiro Oba
of Hokkaido University in Japan says, "Scientists have previously found
nucleobases and vitamins in some carbon-rich meteorites, but there was
always the question of contamination by exposure to the Earth's
environment."
Contamination can be ruled out because the Hayabusa2 mission immediately
gathered two samples from the asteroid Ryugu and sent them to Earth in
sealed capsules.
Humanity is eager to learn the details of how life first appeared and how
widespread it may have been throughout the Milky Way cosmos. One method of
questioning them is to look for the components of life in space and consider
methods for bringing them to earth.
There are many components for living out there, as we are learning more and
more. They have been discovered in masses of star-forming dust that envelop
the center of our galaxy as well as in planet-forming dust. And they have
been discovered in numerous meteors that have impacted the earth after
leaving Earth's atmosphere.
Together, the data points to the possibility that life's fundamental
components may have been extraterrestrial. But until scientists could rule
out the permeation of Earth material into space rocks after they arrived
here, confidence stayed illusive.
Oba and his coworkers used a novel method they devised for the small-scale
detection and labeling of nucleobases in minute quantities to determine what
was in the pure samples Hayabusa2 returned from Ryugu.
The researchers used high-performance liquid chromatography in conjunction
with
electrospray ionization
high-resolution mass spectrometry to analyze the two samples, which were
taken from various parts of the asteroid. This method produced all five
standard nucleobases when applied to the 1969 Murchison asteroid that
impacted Earth.
The experts think the lesser but still important variety of biomolecules
discovered in Ryugu.
Uranium was only present in trace quantities in the samples, between 6 and
32 parts per billion (ppb), while vitamin B3 was more prevalent, between 49
and 99 ppb,
according to Oba. Other organic compounds, such as a variety of amino acids, amines, and
carboxylic acids, which are present in proteins and metabolism,
respectively, were also discovered in the sample.
The newly discovered substances, which join the roughly 20 amino acids
already discovered in Ryugu samples, are distinct from those discovered in
other carbon-rich asteroids that have impacted Earth but are largely
comparable. As a result, it is possible that proteins are widely distributed
in carbonaceous meteorites and may have traveled to Earth during times of
impact.
Scientists think that substances containing nitrogen may have developed
from simpler molecules like formaldehyde, ammonia, and hydrogen cyanide as
to how they ended up on the meteorites.
These have not been discovered in the Ryugu samples, but they may have been
there if the asteroid or its parent body had once been a comet that had been
covered in ices rich in these compounds early in its existence.
But Ryugu is only the beginning. NASA has taken a sample from Bennu,
another asteroid, and is returning it to Earth for examination. Early
research suggests that it also includes organic substances that are
compatible with the components of life.
According to Oba, the discovery of uracil in the Ryugu samples "gives support to the
current theories regarding the source of nucleobases in the early
Earth."
This year, NASA's OSIRIS-REx mission will return fragments from the
asteroid Bennu, and a comparison of the asteroids' compositions will add
more evidence to support these hypotheses.
It appears that the star material from which we are formed took a diversion
through asteroids.
The research has been published in
Nature Communications.
