An artist illustration of the cosmic chemistry cycle. Stars eject matter into space, which forms giant gas and dust clouds. The clouds condense into planets and stars, comets and meteorites.
Credit: Bill Saxton, NRAO/AUI/NSF
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.
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.
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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