http://www.space.com/scienceastronomy/060808_st_life_molecules.html
Organic Molecules Found in Diverse Space
Places
By Ker Than
Staff Writer
posted: 08 August 2006
06:16 am ET
A two-year survey of enormous interstellar dust clouds has turned
up eight organic molecules in two different regions of space. One
is a stellar nursery awash in light while the other is a cold,
starless void.
The finding, detailed in the current issue of Astrophysical
Journal, supports other recent studies suggesting molecules
important for life commonly form in the gas and dust clouds that
condense to form stars and planets.
The molecules were discovered using the Robert C. Byrd Green Bank
Telescope (GBT), a large radio telescope located in West
Virginia.
"Finding eight [organic] molecules in the space of two years is
quite remarkable," said study leader Jan Hollis of NASA Goddard
Space Flight Center.
Life molecules
The newly discovered molecules are made up of 6 to 11 atoms each
and are classified as organic because they contain carbon.
Five of the molecules were discovered in Sagittarius B2(N), a
star-forming dust cloud located 26,000 light-years from Earth near
the center of the Milky Way Galaxy. This stellar nursery is the
largest known repository of complex interstellar molecules.
The other three molecules were found in the Taurus Molecular Cloud
(TMC-1), located only 450 light-years away. TMC-1 is starless; it
is cold and dark and has a temperature of only 10 degrees above
absolute zero.
"The discovery of these large organic molecules in the coldest
regions of the interstellar medium has certainly changed the belief
that large organic molecules would only have their origins in hot
molecular cores," said study team member Anthony Remijan of the
National Radio Astronomy Observatory (NRAO). "It has forced us to
rethink the paradigms of interstellar chemistry."
Just because a molecule is organic does not mean that it is made by
living things. In fact, many of the newly spotted molecules are
poisonous to organisms on Earth, Hollis said. But one of the
molecules found in Sagittarius B2(N), called acetamide, contains a
type of chemical bond important for linking together amino acids,
the molecular building blocks of proteins.
Made up of 9 atoms, acetamide "is the largest molecule found in
space that has that bond," Hollis told SPACE.com.
Space tumbleweeds
The molecules are thought to form by two main mechanisms. In the
first, simple chemical reactions add an atom to a molecule that is
stuck to the surface of a dust grain afloat in space. The second
method involves chemical reactions between neutral molecules and
highly reactive molecules called radicals.
Once formed, the molecules are shaken loose from their dust-grain
homes by rapidly moving shock waves. As the freed molecules tumble
end-over-end in space, they can emit or absorb radiation at precise
radio frequencies unique to each type of molecule. Astronomers
identify the molecules based on these radio frequencies.
Within a dust cloud, thousands of billions of molecules undergo the
same types of rotation, emitting and absorbing the same radio
frequencies. The end result is a signal strong enough to be
detected by instruments on Earth.
The newfound molecules bring the total number of
biologically-relevant molecules found in interstellar space to 141.
Scientists have previously found benzene, a ring-shaped carbon
molecule important for life on Earth, around stars and intact amino
acids in meteorites that have crash-landed on Earth.
Even more complex molecular creations might be possible in space,
experiments suggest. In one study, scientists simulated deep space
conditions in the laboratory and created small structures
resembling cell walls in living organisms.
A case for extraterrestrial life
Taken together, the findings suggest that the chemical ingredients
necessary for life began taking shape long before our planet was
formed.
Many scientists now accept the notion that ancient meteorites and
comets helped jumpstart life on our planet by bringing a
significant amount of water, organic molecules and even amino acids
to early Earth.
Scientists now think those imprisoned organic molecules were likely
created in the massive dust and gas clouds that eventually
coalesced into planets and stars, comets and meteorites. Dust
clouds are thought to form when events such as novas and supernovas
caused chemical elements and molecules created during thermonuclear
reactions inside stars to be ejected into space.
Hollis says his team plans to keep using the Green Bank Telescope
to continue searching for other biologically-significant
molecules.
"From a research and astrobiology point of view, it's been a
goldmine," he said.
