Laser mass spectrometric detection of extraterrestrial aromatic molecules: mini-review and examination of pulsed heating effects.

Laser mass spectrometry is a powerful tool for the sensitive, selective, and spatially resolved analysis of organic compounds in extraterrestrial materials. Using microprobe two-step laser mass spectrometry (muL(2)MS), we have explored the organic composition of many different exogenous materials, including meteorites, interplanetary dust particles, and interstellar ice analogs, gaining significant insight into the nature of extraterrestrial materials. Recently, we applied muL(2)MS to analyze the effect of heating caused by hypervelocity particle capture in aerogel, which was used on the NASA Stardust Mission to capture comet particles. We show that this material exhibits complex organic molecules upon sudden heating. Similar pulsed heating of carbonaceous materials is shown to produce an artifactual fullerene signal. We review the use of muL(2)MS to investigate extraterrestrial materials, and we discuss its recent application to characterize the effect of pulsed heating on samples of interest.

Comment on "Organics captured from comet 81P/Wild 2 by the Stardust spacecraft".

Sandford et al. (Reports, 15 December 2006, p. 1720) reported on organic compounds captured from Comet 81P/Wild 2 by the Stardust spacecraft. We emphasize the difficulty in assigning the origin of compounds detected diffusely along particle impact tracks and show that rapid heating of aerogel that has never been exposed to cometary particle capture can generate complex aromatic molecules from low-mass carbon impurities present in the aerogel.

Organics captured from comet 81P/Wild 2 by the Stardust spacecraft.

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.