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.
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