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Science 14 January 2005:
Vol. 307. no. 5707, pp. 244 - 247
DOI: 10.1126/science.1106717
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Reports

An Astronomical 2175 Å Feature in Interplanetary Dust Particles

John Bradley,1* Zu Rong Dai,1 Rolf Erni,2 Nigel Browning,2,3 Giles Graham,1 Peter Weber,1 Julie Smith,1 Ian Hutcheon,1 Hope Ishii,1 Sasa Bajt,1 Christine Floss,4 Frank Stadermann,4 Scott Sandford5

The 2175 angstrom extinction feature is the strongest (visible-ultraviolet) spectral signature of dust in the interstellar medium. Forty years after its discovery, the origin of the feature and the nature of the carrier(s) remain controversial. Using a transmission electron microscope, we detected a 5.7–electron volt (2175 angstrom) feature in interstellar grains embedded within interplanetary dust particles (IDPs). The carriers are organic carbon and amorphous silicates that are abundant in IDPs and in the interstellar medium. These multiple carriers may explain the enigmatic invariant central wavelength and variable bandwidth of the astronomical 2175 angstrom feature.

1 Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
2 Department of Chemical Engineering, University of California at Davis, CA 95616, USA.
3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
4 Laboratory for Space Sciences, Washington University, St. Louis, MO 63130, USA.
5 Astrophysics Branch, NASA–Ames Research Center, Moffett Field, CA 94035, USA.

* To whom correspondence should be addressed. E-mail: jbradley{at}igpp.ucllnl.org

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