|Sweet Space Products
by Nanni Riccobono (*) - copyright TumblingStone 2001
4.5 billion years ago Earth was
harsh, dry and barren. It has been a while now that scientists
think that comets (dict.)
probably are responsible for water that filled the oceans; but
what about other ingredients of life? Catastrophic impacts with asteroids
(dict.) this is
the point - may as well have supplied amino acids and other
organic compounds used in biology (this theory is called
panspermia, see the box below). Though, something was missing.
One class of ingredients had not been found, Polyhydroxylated
compounds, or polyols, among which there is the sugar you buy in
a store, sugar alcohols and sugar acids, that are vital to all
known life forms. The compounds act as energy sources for all
organisms, they help build proteins and cell membranes, and they
are components of RNA and DNA, the software of life.
A new study now found a variety of polyols in two meteorites (see T.S. special issue number 5 "Meteorites classification"), both thought to have originated in the main asteroid belt between Mars and Jupiter.
The study was led by George Cooper of NASA's Ames Research Center in California and have been presented in the December issue of the journal Nature.
|Now, this is not the first time a piece of rock gains central stage for some life related issue: life on Mars? Life in the Murchison meteorite? It is quite difficult to deal with this kind of discovery because when you find a new meteorite it is new only for us, but it may be on Earth since millions years, becoming so contaminated with terrestrial compounds and elements. In a word, general agreement have never be reached on the ALH84001 meteorite, even if former American president Bill Clinton very formally announced in 1996 that it was the proof that our neighbour planet Mars had hold -once upon a time - forms of life. The same its true for Murchison meteorite.|
Whats different here? The new study found a variety of sugars with varying structures, some very rare on Earth. While some contamination cannot be ruled out, said the researchers, some of the sugars very likely are of extraterrestrial origin.
Now the question is: if there is sugar in space, how did it get there?
Cooper, the study leader, found a wide range of polyols in the two meteorites, and some related molecules called sugar acids. His group also spotted one of the simplest pure sugar molecules, dihydroxyacetone.
Cooper suggests along with his colleagues a
root source for the sugars found in the meteorites. Precursors to
the sugars may originally have formed in interstellar space,
where dust, ice water, ammonia and carbon monoxide were stirred
by starlight in a giant cloud that later formed our Sun and solar
system. These simpler sugar-like substances, if they survived the
formation of the Sun, could then have gotten caught up in
asteroid formation. Simple interstellar molecules were then
stewed in water and condensed to form more complex molecules.
|What is Panspermia?
The word panspermia comes from the Greek, meaning seeds everywhere. This theory was formulated in the 1970s, by two British astronomers, Sir Fred Hoyle and Chandra Wickramasinghe, who suggested that life originated in deep space and was transported around the universe in comets, asteroids, and cosmic dust. Following this theory, freeze-dried bacteria should be contained by interstellar material floating through space. At the time, few working scientists accepted their claims, asserting that chemical analysis of these materials also fits various nonliving carbon compounds. Today, as evidence that life may hitchhike through the universe on comets and asteroids accumulates, astrobiologists theorize that life on Earth may have come from outer space too...
"Mission stardust" - this issue of T.S. : how to collect dust samples from space
"Carbonaceous Meteorites as a Source of Sugar-related Organic Compounds for the Early Earth," by Dr. George Cooper and co-workers at NASA's Ames Research Center, is published in the Dec. 20 issue of Nature
Ames research center:
To know more about ALH84001 and
meteorites from Mars:
About Murchison meteorite:
What is life and where does it