Fullerenes and Noble Gases in the Murchison and Allende Meteorites

Introduction: Since the synthesis, isolation and characterization of fullerenes more than a decade ago, there has been considerable interest in ascertaining whether or not this new family of carbon (C) molecules occur naturally on the Earth or in the Cosmos (e.g. circumstellar shells, interstellar medium or ISM etc.) [1,2,3]. For example, it has been suggested that the fullerene molecule, C60, might be widely distributed in the Universe, particularly in the outflows of C stars, due to its exceptional thermal stability and photochemical properties [4]. Despite an intense effort carried out by the scientific community to verify this hypothesis, only a few unusual natural occurrences of fullerenes have been reported [5-8]. However, all of the terrestrial discoveries have been limited to the detection of mostly C60, C70 and trace amounts of some higher (H) fullerenes (e.g. C78, C84, C100), while extraterrestrial (ET) evidence is limited to trace findings of mostly C60 [9]. The lack of evidence for ET fullerene compounds have thus raised the question of whether or not this form of C is a significant ET carbon phase in meteorites. In this work we are reporting the identification of naturally occurring fullerenes (C100 to C400) in two carbonaceous chondrites (Allende and Murchison). We have applied an extraction protocol developed for the isolation of higher fullerenes in arc evaporated soot [2,3] to the carbonrich acid residues of both meteorites to isolate microgram quantities of fullerene extract. Laser desorption (linear) time-of-flight mass spectrometry (LDMS) was used to confirm the presence of fullerenes in the extracted residue. Because of the unique ability of the fullerene cage structure to encapsulate and retain noble gases for billions of year’s (10), we use the isotopic composition of the encapsulated noble gases to identify the source as extraterrestrial. Data & Results: LDMS analysis of the Murchison C residue extracted with toluene was predominately a kerogenlike C component and revealed only trace amounts of C60 (<1 μg per 60 grams). This toluene extract also contained no anomalous helium above the blank level. Subsequent extraction of the same residue with 1,2,3,5 tetramethylbenzene (TMB) revealed a small peak for C60 +