The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.
The cryptoendolithic habitat of the Antarctic Dry Valleys has been considered a good analogy for past Martian ecosystems, if life arose on the planet. Yet cryptoendoliths are thought to favor the colonization of rocks that have a preexisting porous structure, e.g., sandstones. This may weaken their significance as exact analogues of potential rock‐colonizing organisms on Mars, given our current understanding of the dominant volcanic nature of Martian geology. However, the production of oxalic acid, by these lichen‐dominated communities, and its weathering potential indicate that it could be an aid in rock colonization, enabling endoliths to inhabit a wider variety of rock types. Utilizing ICP‐AES and scanning electron microscope techniques, this study investigates elemental and mineralogical compositions within colonized and uncolonized layers in individual sandstone samples. This is in order to determine if the weathering of mineral phases within the colonized layers causes an increase in the amount of pore space available for colonization. The results show that colonized layers are more weathered than uncolonized, deeper portions of the rock substrate. Layers within uncolonized samples have uniform compositions. Differences between the colonized and uncolonized layers also occur to varying extents within colonized rocks of different mineralogical maturities. The results confirm that cryptoendoliths modify their habitat through the production of oxalic acid and suggest that over time this directly increases the porosity of their inhabited layer, potentially increasing the biomass it can support.
Abstract— We have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the Tagish Lake carbonaceous chondrite by high‐resolution stepped‐combustion mass spectrometry, and compared the results with data from the Orgueil (CI1), Elephant Moraine (EET) 83334 (CM1) and Murchison (CM2) chondrites. The small chip of Tagish Lake analysed herein had a higher carbon abundance (5.81 wt%) than any other chondrite, and a nitrogen content (˜1220 ppm) between that of CI1 and CM2 chondrites. Owing to the heterogeneous nature of the meteorite, the measured carbon abundance might be artificially high: the carbon inventory and whole‐rock carbon isotopic composition (δ 13 C ≅ +24.4% o ) of the chip was dominated by 13 C‐enriched carbon from the decomposition of carbonates (between 1.29 and 2.69 wt%; δ 13 C ≅ +67% o and δ 18 O ≅ +35% o , in the proportions ˜4:1 dolomite to calcite). In addition to carbonates, Tagish Lake contains organic carbon (˜2.6 wt%, δ 13 C ≅ −9% o ; 1033 ppm N, δ 15 N ≅ +77% o ), a level intermediate between CI and CM chondrites. Around 2% of the organic material is thermally labile and solvent soluble. A further −18% of the organic species are liberated by acid hydrolysis. Tagish Lake also contains a complement of presolar grains. It has a higher nanodiamond abundance (approximately 3650–4330 ppm) than other carbonaceous chondrites, along with ˜8 ppm silicon carbide. Whilst carbon and nitrogen isotope geochemistry is not diagnostic, the data are consistent with classification of Tagish Lake as a CI2 chondrite.
Angrites are a small group of silica undersaturated achondrites notable for their apparent lack of shock features or brecciation and their characteristic unusual mineralogy. We are interested in studying their magmatic history, as reflected by their light-element chemistry. Here, we report on the abundance, distribution and isotopic composition of nitrogen in a suite of 5 angrites. We employed the technique of stepped oxidation, which has previously been used to determine the nitrogen chemistry of a variety of meteoritic and terrestrial rocks.
We introduce the principal mysteries surrounding comets; discuss the proposed importance of comets to the origin of water and organic compounds in the inner solar system; and summarize the history of cometary observation, study, and exploration over the past 22 centuries.
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