NASA develops key to cosmic carbon's molecular evolution

May 14, 2013 by Ruth Dasso Marlaire
For the first time, scientists are able to automatically interpret previously unknown infrared emissions from space that come from surprisingly complex organic molecules, called polycyclic aromatic hydrocarbons (PAHs), which are abundant and important across the universe. They use spectra of infrared radiation to identify unknown substances in space. These spectra are as good as fingerprints for identification purposes. Analyzing the PAH bands represents a powerful new astronomical tool to trace the evolution of cosmic carbon and, at the same time, probe conditions across the universe. Credit: NASA Ames

(Phys.org) —Scientists at NASA's Ames Research Center, Moffett Field, Calif., now have the capability to systematically investigate the molecular evolution of cosmic carbon. For the first time, these scientists are able to automatically interpret previously unknown infrared emissions from space that come from surprisingly complex organic molecules, called polycyclic aromatic hydrocarbons (PAHs), which are abundant and important across the universe.

Between 2003 and 2005, thanks to its unprecedented sensitivity, NASA's , managed and operated by NASA's Jet Propulsion Laboratory, Pasadena, Calif., created maps of the tell-tale PAH signature across large regions of space, from hot regions of harsh ultraviolet (UV) radiation close to stars, to cold, dark clouds where stars and planets form. By exclusively using their unique collection of authentic PAH spectra, coupled with algorithm-driven, blind-, scientists at Ames were able to interpret the cosmic infrared maps with . They found that PAHs changed significantly in size, electrical charge and structure, to adjust to the different environment at each spot in the map. Carbon is one of the most abundant atoms in space and scientists believe that the spectral changes across these maps trace the of carbon across the universe.

"At the time of our discovery that the 'signature,' or identifying spectrum, of this unexpected, but common infrared (IR) radiation from space hinted that PAHs might be responsible, we were limited to a handful of small PAHs, very few were available to study," said Louis Allamandola, an astrophysics researcher at Ames. "To test the idea that PAHs were responsible, we measured and computed PAH spectra under astronomical conditions, creating the world's largest collection of PAH spectra. Today, our collection contains more than 700 PAH spectra."

Results will be published May 14 in "Properties of PAHs in the Northwest PDR of NGC 7023 1: PAH size, charge, composition and structure distribution," Astrophysical Journal, vol. 769 (2) article 117, 2013.

To determine the spectral changes across these maps, these astrophysicists used the PAH spectra collected in the PAH IR Spectroscopic Database at Ames. They analyzed the Spitzer IR map of the Iris Nebula (NGC 7023) that hosts both the extreme environment of a region close to a star as well as the more shielded, benign environment of a cold molecular cloud.

Between 2003 and 2005, thanks to its unprecedented sensitivity, NASA’s Spitzer Space Telescope created maps of the tell-tale PAH signature across large regions of space. Credit: NASA JPL

The new maps showed that small, electrically neutral, irregularly-shaped PAHs are most important near the cold molecular cloud that is far from the star that excites PAH emission. However, when PAHs move closer to the exciting star and away from the cold cloud, they become large, symmetric and are electrically charged. "The large PAHs take over because they are more robust than the smaller, irregularly-shaped PAHs, which are destroyed by the unshielded star light," said Christiaan Boersma, an astrophysicist at Ames.

Finally, these large PAHs are themselves broken down, as they are stripped of hydrogen and become small fragments. At this point, the emission from the dehydrogenated PAHs takes over in the observed region. There were two findings that are especially important: the first is that positively-charged, nitrogen-containing PAH cations are needed to complete the match between the correct spectral signature and the observed emission, and the second is that dehydrogenation and fragmentation occur close to the exciting star.

"The indication of nitrogen-containing PAHs (PANHs) is significant, as these have not been seriously considered previously. They represent an important class of prebiotic molecules, which are precursors to life," said Jesse Bregman, also an astrophysicist at Ames. "If borne out, this indicates complex, nitrogen-containing, aromatic molecules are present across the universe."

This approach of analyzing the aromatic infrared bands using the spectra of individual PAHs provides new, fundamental information about the UV-driven, spatial evolution of PAH subpopulations. It also ties these variations to changes in local conditions such as those due to the physical shape and history of the region, radiation field, and so on.

"Spitzer detected the PAH signature across the universe and showed PAHs were already forming only a couple of billion years after the Big Bang. Since PAHs are so sensitive to local conditions, analyzing the PAH bands as we did here represents a powerful new astronomical tool to trace the evolution of cosmic carbon and, at the same time, probe conditions across the universe," concluded Allamandola.

Explore further: Planet-forming lifeline discovered in a binary star system

More information: dx.doi.org/10.1088/0004-637X/769/2/117

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GSwift7
not rated yet May 15, 2013
wow, this should be a really big deal. It sounds kinda like how useful the H-R diagram is, since it allows you to infer a lot of data about an area/object just by observing one or two characteristics. The fact that it appears to work even with the oldest galaxies is also huge, since that lets us know details about them which would otherwise be too far away to see.

The nitrogen chemistry is also interesting for astrobiologists, but I don't think that's as big a deal as the discovery of the patterns in the carbon chemistry. Every time we find a tool that tells us whether two things are the same or not, even when we can't clearly see both of them, is a powerful tool.
Fleetfoot
not rated yet May 15, 2013
Adding nitrogen is a major step in identifying pre-biotic chemicals and perhaps clues to the chemistry of abiogenesis. I think that's extremely important for most people, though perhaps less so for astronomers.
GSwift7
not rated yet May 15, 2013
Sure it is an important discovery, but I thought we kinda always assumed that this was the case in far away places, just as it is here in the Milkyway. Sure it is nice to confirm, that this kind of organic chemistry was happening as far back as 12 billion years ago, but that doesn't change much in regard to our search for life in the Milkyway, does it?
Fleetfoot
not rated yet May 15, 2013
Sure it is an important discovery, but I thought we kinda always assumed that this was the case in far away places, just as it is here in the Milkyway. ...


From the article:

"The indication of nitrogen-containing PAHs (PANHs) is significant, as these have not been seriously considered previously."

AFAIK nitrogen in interstellar molecules hasn't been confirmed before even in the Milky Way.
GSwift7
not rated yet May 16, 2013
AFAIK nitrogen in interstellar molecules hasn't been confirmed before even in the Milky Way


Here's the wiki on Nitrogen:

http://en.wikiped...Nitrogen

From that page:
Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer


Nitrogen is the 7th most common element. We see nitrogen compounds all over the Milkyway. However, nitrogen is formed from fusion of carbon in supernovae, so it should be less common in the early Universe. It's strange how we keep finding signs that the Universe matured so much faster than we thought it could.
Fleetfoot
not rated yet May 16, 2013
AFAIK nitrogen in interstellar molecules hasn't been confirmed before even in the Milky Way


Here's the wiki on Nitrogen:

http://en.wikiped...Nitrogen

From that page:
Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer


Nitrogen is the 7th most common element. We see nitrogen compounds all over the Milkyway. However, nitrogen is formed from fusion of carbon in supernovae, so it should be less common in the early Universe. It's strange how we keep finding signs that the Universe matured so much faster than we thought it could.


Sorry, I should have been clearer. Of course simple molecules like HCN have known for some time but I'm not aware of nitrogen in more complex molecules like PAH. However, this field moves so fast I may well not be up to date.
Torbjorn_Larsson_OM
not rated yet May 18, 2013
The find of PANHs are nice, but more as a confirmation of the general CHNOS pathway of dust and then watery asteroids which makes PANSHs (nitrogen- and sulfur-containing PAHs).

When people were finally able to dig deep into autotroph metabolism, they got homologies between the first methano- and acetogens and pH modulated alkaline hydrothermal vents (Lane & Martin 2012). So we know our biosphere didn't get kick-started by external organics. It also lowers expectations that chemical evolution elsewhere would produce life, since it seems the metabolic homologies were central.

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