Claude Ricketts Maechling

Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and iron sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

Identification of Complex Aromatic Molecules in Individual Interplanetary Dust Particles

Seventeen stratospherically collected particles—eight of which are classified as interplanetary dust particles (IDPs), seven of which are classified as probable terrestrial contaminants, and two of which have uncertain origins—were studied with a microprobe two-step laser mass spectrometer. Many polycyclic aromatic hydrocarbons(PAHs) and their alkylated derivatives were identified in two of the eight IDPs. The PAHs observed include a high-mass envelope not found in meteorites or terrestrial contaminants and prominent odd-mass peaks suggestive of nitrogen-containing functional groups attached to aromatic chromophores. In addition, the complexity of the IDP mass spectra has no precedence in previous studies of meteorite samples or their acid residues. Extensive checks were performed to demonstrate that the PAH signals are not caused by terrestrial contaminants.

An asteroidal breccia: The anatomy of a cluster IDP

Abstract We report results of a consortium study of a large interplanetary dust particle known as cluster L2008#5. This cluster is composed of fifty-three fragments (>5 pm in diameter) and several hundred fines ( Several methods were used to estimate the degree of heating that this cluster experienced. Variations in the inferred peak temperatures experienced by different fragments suggest that a thermal gradient was maintained. The cluster as a whole was not strongly heated; it is estimated to have a low earth-encounter velocity which is consistent with origin from an object in an asteroidal orbit rather than from a comet, which would most likely have a high entry velocity. Our conclusions show that cluster L2008#5 consists of a chemically and mineralogically diverse mixture of fragments. We believe that cluster L2008#5 represents a heterogeneous breccia and that it was most likely derived from an object in an asteroidal orbit. We also present an important cautionary note for attempts to interpret individual, small-sized 10–15 μm IDPs as representative of parent bodies. It is not unique that individual building blocks of IDPs, such as discrete olivine, pyroxene, sulfide grains, regions of carbonaceous material, and other noncrystalline material, are found in several fragments; however, it is unique that these building blocks are combined in various proportions in related IDPs from one large cluster particle.

Evidence for thermalization of surface‐desorbed molecules at heating rates of 108 K/s

Laser desorption of aniline‐d7 from a single‐crystal surface (0001) of sapphire (Al2O3) at a heating rate on the order of 108 K/s was studied using pulsed infrared laser radiation for desorption and resonance enhanced multiphoton ionization (REMPI) for detection of the desorbed aniline molecules. On the basis of single‐vibronic‐level fluorescence (SVLF) spectra we unambigiously assign the 10b transition. REMPI spectroscopy provides vibrational temperatures and therefore describes the internal energy distribution, whereas the time‐of‐flight (TOF) profiles provide translational temperatures. All results are consistent with a thermal mechanism for desorption, i.e., pulsed heating of the sapphire surface on the nanosecond time scale leads to thermal desorption and rapid thermalization of the escaping molecules.

13C/12C ratio measurements of aromatic molecules using photoionization with TOF mass spectrometry

We demonstrate a method for measuring the carbon isotope ratios of aromatic molecules without the need for chemical preparation. The technique employs a time-of-flight (TOF) mass spectrometer equipped with a dual microchannel plate detector assembly. We present the measurement of carbon isotope ratios for m-xylene-d,, (C,D,(CD,),), toluene (C,H,CH,), and toluene-d, (C+CD,). Gas-phase samples are photoionized with the 266 nm output of a Nd:YAG laser, and the abundance of “C and C in the molecules is derived from the TOF spectra. Complications caused by and corrections for detector nonlinearity and parent ion fragmentation are discussed.