POLYCYCLIC AROMATIC-HYDROCARBONS (PAHS) IN ANTARCTIC MARTIAN METEORITES, CARBONACEOUS CHONDRITES, AND POLAR ICE

Recent analyses of the carbonate globules present in the Martian meteo rite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level (McKay et al., 1996). The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps der ived from an ancient martian biota. We have examined PAHs in the Antar ctic shergottite EETA79001, which is also considered to be from Mars, as well as several Antarctic carbonaceous chondrites. We have found th at many of the same PAHs detected in the ALH84001 carbonate globules a re present in Antarctic carbonaceous chondrites and in both the matrix and carbonate (druse) component of EETA79001. We also investigated PA Hs in polar ice and found that carbonate is an effective scavenger of PAHs in ice meltwater. Moreover, the distribution of PAHs in the carbo nate extract of Antarctic Allan Hills ice is remarkably similar to tha t found in both EETA79001 and ALH84001. The reported presence of L-ami no acids of apparent terrestrial origin in the EETA79001 druse materia l (McDonald and Bada, 1995) suggests that this meteorite is contaminat ed with terrestrial organics probably derived from Antarctic ice meltw ater that had percolated through the meteorite. Our data suggests that the PAHs observed in both ALH84001 and EETA79001 are derived from eit her the exogenous delivery of organics to Mars or extraterrestrial and terrestrial PAHs present in the ice meltwater or, more likely, from a mixture of these sources. It would appear that PAHs are not useful bi omarkers in the search for extinct or extant life on Mars. Copyright ( C) 1997 Elsevier Science Ltd.