[meteorite-list] PSI Research Points to Better Understanding of Carbon in Comets

[Ron Baalke]

NEWS RELEASE FROM THE PLANETARY SCIENCE INSTITUTE

SENT: 
Dec. 13, 2010

FROM: 
Alan Fischer
Public Information Office
Planetary Science Institute
520-622-6300
520-885-5648
fischer at psi.edu

PSI Research Points to Better Understanding of Carbon in Comets

Using a comet as a far-flung laboratory, a Planetary Science 
Institute researcher has shown that the ionization lifetime of 
carbon is much shorter than what is currently used in calculations 
by comet scientists.

An accurate ionization lifetime is critical to understanding the 
amount of carbon released from comets, said Jeff Morgenthaler, 
senior scientist at PSI. A shorter lifetime suggests that the 
carbon content of some comets may be lower than previously 
estimated. This work could affect current ideas about where 
comets formed in the early solar system and the role they may 
have played in bringing the seeds of life to Earth.

"Carbon is an important atom for lots of reasons," Morgenthaler 
said. "We need to know how much carbon there is in comets and in 
what molecules it can be found to answer some of the questions 
that have been posed."

Using wide-field images recorded by the Galaxy Evolution Explorer 
(GALEX) satellite, Morgenthaler produced extremely high-quality 
radial profiles of atomic carbon emissions from comet C/2004 Q2 
(Machholz).

Unlike conditions seen on Earth, a comet's coma, or envelope 
around its nucleus, is a very simple atmosphere with no gravity 
and no magnetic field, and is only affected by the solar photon 
and solar wind environment, Morgenthaler said.

"Since other researchers have established how fast the carbon 
moves away from the comet, we could use the fall-off of the light 
as a function of distance to measure how long the carbon lives in 
the interplanetary medium before it is ionized," said Morgenthaler, 
lead author of a recent paper on the topic that appeared in the 
Astrophysical Journal.

"We got a chance to check a lot of calculations at once with our 
measurement," he said. "We found that a carbon atom is ionized 
after seven to 16 days, depending on solar activity and solar 
wind conditions."

This marks the end point of the destruction of all of the more 
complex carbon-bearing molecules found in comets.  

Researchers have used the presence of long-chain carbon-containing 
molecules in comets, including some simple amino acids, as evidence 
that comets may have brought the seeds of life to Earth. "We need to 
pull back a few more layers of the onion to see if the signatures of 
the long-chain carbon-bearing molecules are detectable in these data," 
Morgenthaler said.  "We definitely see the signatures of carbon 
monoxide and methane."

The research found that more than just sunlight was affecting the 
carbon from the comet.

"Something was hitting the carbon: the solar wind," he said. "This 
had been predicted earlier, but until now no one had quantitatively 
put all the pieces together and done a measurement that confirmed it."

The research was funded by a grant to PSI from the GALEX Guest 
Investigator program.

GALEX's wide field of view at 1 degree is 10 times larger than the 
typical ultraviolet telescopes used for similar research, he said. 
This allows GALEX to capture essentially all the emission from the 
comet, resulting in far more accurate results.

Co-authors of the Astrophysical Journal paper are Walter M. Harris, 
Department of Applied Sciences, University of California at Davis; 
Michael R. Combi, Department of Atmospheric, Oceanic and Space 
Sciences, The University of Michigan; Paul D. Feldman, Department 
of Physics and Astronomy, The Johns Hopkins University; Harold A. 
Weaver, Space Department, Johns Hopkins University Applied Physics 
Laboratory.


CONTACT:
Jeff Morgenthaler
Senior Scientist
207-231-4036
jpmorgen at psi.edu


PSI INFORMATION:
Mark V. Sykes
Director
520-622-6300
sykes at psi.edu