[meteorite-list] Vitamin B3 Might Have Been Made in Space, Delivered to Earth by Meteorites

[Ron Baalke]

http://www.nasa.gov/content/goddard/vitamin-b3-might-have-been-made-in-space-delivered-to-earth-by-meteorites/ 


Vitamin B3 Might Have Been Made in Space, Delivered to Earth by Meteorites
Bill Steigerwald
NASA's Goddard Space Flight Center, Greenbelt, Md.
william.a.steigerwald at nasa.gov
April 17, 2014

Ancient Earth might have had an extraterrestrial supply of vitamin B3 
delivered by carbon-rich meteorites, according to a new analysis by NASA-funded 
researchers. The result supports a theory that the origin of life may 
have been assisted by a supply of key molecules created in space and brought 
to Earth by comet and meteor impacts.

"It is always difficult to put a value on the connection between meteorites 
and the origin of life; for example, earlier work has shown that vitamin 
B3 could have been produced non-biologically on ancient Earth, but it's 
possible that an added source of vitamin B3 could have been helpful," 
said Karen Smith of Pennsylvania State University in University Park, 
Pa. "Vitamin B3, also called nicotinic acid or niacin, is a precursor 
to NAD (nicotinamide adenine dinucleotide), which is essential to metabolism 
and likely very ancient in origin." Smith is lead author of a paper on 
this research, along with co-authors from NASA's Goddard Space Flight 
Center in Greenbelt, Md., now available online in the journal Geochimica 
et Cosmochimica Acta.

This is not the first time vitamin B3 has been found in meteorites. In 
2001 a team led by Sandra Pizzarello of Arizona State University, in Tempe 
discovered it along with related molecules called pyridine carboxylic 
acids in the Tagish Lake meteorite.

In the new work at Goddard's Astrobiology Analytical Laboratory, Smith 
and her team analyzed samples from eight different carbon-rich meteorites, 
called "CM-2 type carbonaceous chondrites" and found vitamin B3 at levels 
ranging from about 30 to 600 parts-per-billion. They also found other 
pyridine carboxylic acids at similar concentrations and, for the first 
time, found pyridine dicarboxylic acids.

"We discovered a pattern - less vitamin B3 (and other pyridine carboxylic 
acids) was found in meteorites that came from asteroids that were more 
altered by liquid water. One possibility may be that these molecules were 
destroyed during the prolonged contact with liquid water," said Smith. 
"We also performed preliminary laboratory experiments simulating conditions 
in interstellar space and showed that the synthesis of vitamin B3 and 
other pyridine carboxylic acids might be possible on ice grains."

Scientists think the solar system formed when a dense cloud of gas, dust, 
and ice grains collapsed under its own gravity. Clumps of dust and ice 
aggregated into comets and asteroids, some of which collided together 
to form moon-sized objects or planetesimals, and some of those eventually 
merged to become planets.

Space is filled with radiation from nearby stars as well as from violent 
events in deep space like exploding stars and black holes devouring matter. 
This radiation could have powered chemical reactions in the cloud (nebula) 
that formed the solar system, and some of those reactions may have produced 
biologically important molecules like vitamin B3.

Asteroids and comets are considered more or less pristine remnants from 
our solar system's formation, and many meteorites are prized samples from 
asteroids that happen to be conveniently delivered to Earth. However, 
some asteroids are less pristine than others. Asteroids can be altered 
shortly after they form by chemical reactions in liquid water. As they 
grow, asteroids incorporate radioactive material present in the solar 
system nebula. If enough radioactive material accumulates in an asteroid, 
the heat produced as it decays will be sufficient to melt ice inside the 
asteroid. Researchers can determine how much an asteroid was altered by 
water by examining chemical and mineralogical signatures of water alteration 
in meteorites from those asteroids.

When asteroids collide with meteoroids or other asteroids, pieces break 
off and some of them eventually make their way to Earth as meteorites. 
Although meteorites are valued samples from asteroids, they are rarely 
recovered immediately after they fall to Earth. This leaves them vulnerable 
to contamination from terrestrial chemistry and life.

The team doubts the vitamin B3 and other molecules found in their meteorites 
came from terrestrial life for two reasons. First, the vitamin B3 was 
found along with its structural isomers - related molecules that have 
the same chemical formula but whose atoms are attached in a different 
order. These other molecules aren't used by life. Non-biological chemistry 
tends to produce a wide variety of molecules -- basically everything permitted 
by the materials and conditions present -- but life makes only the molecules 
it needs. If contamination from terrestrial life was the source of the 
vitamin B3 in the meteorites, then only the vitamin should have been found, 
not the other, related molecules.

Second, the amount of vitamin B3 found was related to how much the parent 
asteroids had been altered by water. This correlation with conditions 
on the asteroids would be unlikely if the vitamin came from contamination 
on Earth.

The team plans to conduct additional interstellar chemistry experiments 
under more realistic conditions to better understand how vitamin B3 can 
form on ice grains in space. "We used pyridine-carbon dioxide ice in the 
initial experiment," said Smith. "We want to add water ice (the dominant 
component of interstellar ices) and start from simpler organic precursors 
(building-block molecules) of vitamin B3 to help verify our result."

Smith performed the research at Goddard as a graduate student at Pennsylvania 
State University, University Park, Pa. Funding came from the Penn State 
Astrobiology Research Center and the Goddard Center for Astrobiology via 
the NASA Astrobiology Institute. The research was also funded by the NASA 
Pennsylvania Space Grant Consortium and the NASA Cosmochemistry Program.

For more information about the Tagish Lake meteorite, visit:

http://www.nasa.gov/centers/goddard/news/features/2011/tagish-lake.html