Vitamin B3 could have been made on icy dust grains in
space, and later delivered to Earth by meteorites and comets, according
to new laboratory experiments by a team of NASA-funded researchers.
Vitamin B3, also known as niacin or nicotinic acid, is used
to build NAD (nicotinamide adenine dinucleotide), which is essential to
metabolism and probably ancient in origin. The result supports a theory
that the origin of life may have been assisted by a supply of
biologically important molecules produced in space and brought to Earth
by comet and meteor impacts.
The new work builds on earlier research by the team in which they analyzed carbon-rich meteorites and discovered that vitamin B3
was present at concentrations ranging from about 30 to 600
parts-per-billion. In that work, the team performed preliminary
laboratory experiments that showed vitamin B3 could be made
from a simpler building-block organic molecule called pyridine in carbon
dioxide ice under conditions that simulated the environment in space.
The new experiments made the simulation more realistic by adding
water ice to the mixture and using amounts closer to what is expected
for interstellar ices and comets. The team found that even with the
addition of water, the vitamin could be made under a wide variety of
scenarios where the water ice abundance varied by up to ten times.
"We found that the types of organic compounds in our
laboratory-produced ices match very well to what is found in
meteorites," said Karen Smith of NASA's Goddard Space Flight Center in
Greenbelt, Maryland. "This result suggests that these important organic
compounds in meteorites may have originated from simple molecular ices
in space. This type of chemistry may also be relevant for comets, which
contain large amounts of water and carbon dioxide ices. These
experiments show that vitamin B3 and other complex organic
compounds could be made in space and it is plausible that meteorite and
comet impacts could have added an extraterrestrial component to the
supply of vitamin B3 on ancient Earth."
Smith, who is lead author of a paper on this research published
online June 17, 2015 in Chemical Communications, performed the work with
her team at NASA Goddard, including her postdoctoral research advisor,
Perry Gerakines of NASA Goddard. "This work is part of a broad research
program in the field of Astrobiology at NASA Goddard," Gerakines said.
"We are working to understand the origins of biologically important
molecules and how they came to exist throughout the Solar System and on
Earth. The experiments performed in our laboratory demonstrate an
important possible connection between the complex organic molecules
formed in cold interstellar space and those we find in meteorites."
Exploding stars (supernovae) and the winds from red giant stars near
the end of their lives produce vast clouds of gas and dust. Solar
systems are born when shock waves from stellar winds and other nearby
supernovae compress and concentrate a cloud of ejected stellar material
until dense clumps of that cloud begin to collapse under their own
gravity, forming a new generation of stars and planets.
This is an artist's concept of a protoplanetry disk
surrounding a forming star that is ejecting jets of material (yellow
beams). Such disks contain countless tiny dust grains, many of which
become incorporated into asteroids, comets, and planets. Credits: NASA Goddard. Hi-res image
These clouds contain countless dust grains. Just as frost forms on car
windows during cold, humid nights, carbon dioxide, water, and other
gases form a layer of frost on the surface of these grains. Radiation in
space powers chemical reactions in this frost layer to produce complex
organic molecules, possibly including vitamin B3. The icy
grains become incorporated into comets and asteroids, some of which
impact young planets like ancient Earth, delivering the organic
molecules contained within them.
This is an artist's concept of a nebula containing gas, dust, and asteroids that will later form stars and planets.
Credits: NASA Goddard
The researchers tested this theory by simulating the space environment
in the Cosmic Ice Laboratory at NASA Goddard. An aluminum plate cooled
to around minus 423 degrees Fahrenheit (minus 253 Celsius) was used to
represent the frigid surface of an interstellar dust grain. The plate
was chilled in a vacuum chamber to replicate space conditions, and gases
containing water, carbon dioxide, and pyridine were released into the
chamber, where they froze onto the plate. The plate was then bombarded
with protons at about 1 million volts from a particle accelerator to
simulate space radiation.
A picture of the aluminum plate with a chemical deposit on it.
Credits: Karen Smith/NASA Goddard
The team performed an initial analysis of the contents of the frozen layer by shining infrared light on it to identify absorption patterns – certain molecules absorb infrared light at specific colors, or frequencies. The plate was then heated to room temperature so the ice residue could be analyzed in greater detail at Goddard's Astrobiology Analytical Laboratory. The team found that this experiment produced a variety of complex organic molecules, including vitamin B3.
Observations from the European Space Agency's Rosetta mission, now in
orbit around Comet 67P/Churyumov-Gerasimenko, might add more support to
the theory that comets brought organic matter to Earth. "Rosetta could
help validate these experiments if it finds some of the same complex
organic molecules in the gases released by the comet or in the comet’s
nucleus," said Smith.
This work was supported by a NASA Postdoctoral Program Fellowship
administered by Oak Ridge Associated Universities through a contract
with NASA, the NASA Astrobiology Institute (NAI)
via the Goddard Center for Astrobiology (GCA), and the NASA
Cosmochemistry Program. NASA's Ames Research Center in Mountain View,
California, administers the NAI.
Bill Steigerwald
NASA Goddard Space Flight Center, Greenbelt, Maryland
