[meteorite-list] NASA Reveals Key to Unlock Mysterious Red Glow in Space (PAHs)

[Ron Baalke]

Aug. 2, 2010

Ruth Dasso Marlaire                                             
Ames Research Center, Moffett Field, Calif.
650-604-4709
ruth.marlaire at nasa.gov

RELEASE: 10-65AR

NASA REVEALS KEY TO UNLOCK MYSTERIOUS RED GLOW IN SPACE 

MOFFETT FIELD, Calif. -- NASA scientists created a unique 
collection of polycyclic aromatic hydrocarbon (PAH) spectra 
to interpret mysterious emission from space. Because PAHs 
are a major product of combustion, remain in the environment, 
and are carcinogenic, the value of this PAH spectral collection 
extends far beyond NASA and astronomical applications.

For years, scientists have been studying a mysterious infrared 
glow from the Milky Way and other galaxies, radiating from  
dusty regions in deep space. By duplicating the harsh conditions 
of space in their laboratories and computers, scientists have 
identified the mystifying infrared emitters as PAHs. PAHs are 
flat, chicken-wire shaped, nano-sized molecules that are very 
common on Earth.

"PAHs in space are probably produced by carbon-rich, giant stars. 
A similar process produces soots here on Earth," said Louis 
Allamandola, an astrochemistry researcher at NASA's Ames Research 
Center, Moffett Field, Calif. "Besides astronomical applications, 
this PAH database and software can be useful as a new research tool 
for scientists, educators, policy makers, and consultants working 
in the fields of medicine, health, chemistry, fuel composition, 
engine design, environmental assessment, environmental monitoring, 
and environmental protection."

To manage the research data, NASA built a database that now can be 
shared over the internet. It's the world's largest collection of 
PAH infrared data, and the website contains nearly 700 spectra of 
PAHs in their neutral and electrically charged states. In addition, 
it has tools to download PAH spectra ranging in temperature from 
minus 470 to 2000 degrees Fahrenheit. Thanks to these spectra, PAHs 
are now known to be abundant throughout the universe, but in exotic 
forms not readily found on Earth.

This mysterious infrared radiation from interstellar space was 
discovered in the 1970's and 1980's. While the infrared signature 
hinted that PAHs might be responsible, laboratory spectra of only 
a handful of small, individual PAHs were available to test this 
idea. To make matters worse, these were only for neutral, solid 
PAHs; they were not representative of PAHs found in space, where 
they'd be electrically charged, very cold, individual molecules 
floating in the gas.

By the mid-1990's, observations showed this infrared emission as 
surprisingly common and widespread across the universe, implying 
that the unknown carrier was abundant and important. To better 
understand PAHs, then thought to be too complex to be present in 
space, their spectra were measured under astronomical conditions.

To capture their spectra, Allamandola led a team of scientists to 
measure PAH spectra under simulated astronomical conditions and 
with computer software. This team consisted of experts in many 
different fields. 

"This group made a tremendous effort to make this a reality," said 
Allamandola. "There are now nearly 700 spectra in the database. Six 
hundred of these have been theoretically computed, and sixty have 
been measured in the laboratory. The theoretical spectra span the 
range from two to 2000 microns, the experimental spectra cover two 
to 25 microns."

The spectra have given insights into the PAHs in space that were 
impossible to get any other way. Scientists predict that in the 
near future these spectra will be especially valuable for 
interpreting observations made with NASA's new airborne observatory, 
the Stratospheric Observatory for Infrared Astronomy (SOFIA) and 
the recently launched European Space Agency's (ESA) Herschel 
Telescope.  

They tried to make the website user friendly for researchers. One 
can explore the database by charge, composition and spectral 
signatures. Tools allow users to do analyses online. For example, 
spectra can be combined to create a "composite" signature that can 
be compared directly to the spectrum of "unknown" material. 

We will expand the database and tools," said Christiaan Boersma, a 
NASA postdoctoral fellow at Ames, who designed and developed many 
parts of the website and tools. "We now use the database to 
interpret astronomical observations from star and planet forming 
regions in our galaxy, the Milky Way, and even other galaxies."

"Initially, our hope was to help interpret the experimental spectra, 
but over time, our computational capabilities made it possible to 
study molecules much larger than can be studied in the laboratory," 
said Charles Bauschlicher Jr., a world-renowned computational chemist 
at Ames.

"Thanks to the great sensitivity of the Spitzer Telescope, PAHs are 
seen across the universe, removing any doubt of the importance of 
these species," said Allamandola.  

The database is available at http://www.astrochem.org/pahdb 

More information about the database and graphics are available at 
http://www.astrochem.org/pahdb/pressrelease 

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