Processing of cometary grains at the nucleus surface

Cometary material inevitably undergoes chemical changes before and on leaving the nucleus. In seeking to explain comets as the origin of many IDPs (interplanetary dust particles), an understanding of potential surface chemistry is vital. Grains are formed and transformed at the nucleus surface; much of the cometary volatiles may arise from the organic material. In cometary near-surface permafrost, one expects cryogenic chemistry with crystal growth and isotope. This could be the hydrous environment where IDPs form. Seasonal and geographic variations imply a range of environmental conditions and surface evolution. Interplanetary dust impacts and electrostatic forces also have roles in generating cometary dust. The absence of predicted cometary dust envelopes is compatible with the wide range of particle structures and compositions. Study of IDPs would distinguish between this model and alternatives that see comets as aggregates of core-mantle grains built in interstellar clouds.     

Nitrous oxide production and denitrification rates in estuarine intertidal saltmarsh and managed realignment zones

Increasing concerns over habitat loss and rising costs of sea defence maintenance due to rising sea levels, has seen increases in the practice of managed realignment and reflooding of former reclaimed areas of intertidal saltmarsh and mudflat around the world. These practices are taking place with little knowledge of their impact on soil biogeochemical processes. Rates of denitrification (using the acetylene inhibition technique) and nitrous oxide (N₂O) production were measured from a long-established saltmarsh (SM) and an adjacent, recently re-flooded managed realignment (MR) site comprising former arable land in the estuary of the River Torridge, Devon, UK. Incubations were carried out in closed chambers in which patterns of tidal flooding were simulated automatically. Measurements were made during periods of flood and non-flood over a total of four tidal inundations with estuarine water. During the latter two flooding episodes floodwater was amended with nitrate (NO₃⁻). Nitrous oxide production in the SM soil generally was lower than in the MR soil, with mean values and standard errors over the whole incubation of 0.27 ± 0.16 mg N₂O-N m⁻² h⁻¹ and 0.65 ± 0.15 mg N₂O-N m⁻² h⁻¹ respectively. Denitrification rates demonstrated a similar trend although generally were an order of magnitude higher than N₂O production, with mean rates and standard errors of 2.88 ± 1.12 mg N₂O-N m⁻² h⁻¹ in the SM soil and 3.39 ± 1.16 mg N₂O-N m⁻² h⁻¹ in the MR soil. The data suggest that both soils are net sinks for NO₃⁻ and net sources for N₂O. Both patterns of tidal inundation and floodwater chemistry affect the process rates in each soil differently. The impact of flooding with NO₃⁻ – amended water was greater on the SM soil than the MR soil, and it is likely that decomposing vegetation buried in the accreting sediments following reflooding at the MR site were supplying a source of N in the soil, and so process rates were less dependent upon external supplies. The act of managed realignment in intertidal zones could therefore result in an increase in mean production of N₂O in intertidal zones, at least in the short term.     

The infrared excess from the white dwarf star G29-38: A brown dwarf of dust?

The recently-observed infrared excess from the white dwarf star G29-38 is shown to be better fitted by a model involving organic dust grains, than one involving a brown-dwarf companion star.     

Diatoms on earth,comets, europa and in interstellar space

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 », which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of a cosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.     

A model of the 2–4Μm spectrum of Comet Halley

Recent observations of Halley's Comet show a broad absorption band centred at 3.4 m and which can be explained on the basis of a bacterial grain model.     

The Spectroscopic Idebtification of Interstellar Grains

It is shown that the condition of matching the 3.3–3.9 μm spectrum of the galactic infrared source GC-IRS 7 leads to a remarkably tight convergence on the transmittance curve measured in the laboratory for the dessicated bacterium E. coli.Other materials, including certain biochemicals and postulated prebiologic compounds, are shown to be deficient with regard to meeting this condition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared spectroscopy over the 2.9–3.9 μm waveband in biochemistry and astronomy

The infrared spectrum of the galactic centre source IRS 7 over the 2.9–3.9 m waveband is interpreted as strong evidence for bacterial grains.     

The viability with respect to temperature,of micro-organisms incident on the Earth's atmosphere

Using laboratory measurements of the resistance of E. coli to flash-heating, it is shown that a large fraction of interplanetary micro-organisms in prograde orbits could be added to the Earth without losing viability due to heating by the atmospheric gases.     

A Balloon Experiment to detect Microorganisms in the Outer Space

The results of biological studies of a cryosampler flown with a balloon, in which air samples were collected at altitudes ranging from 20 to 41 km, well above the Tropopause over Hyderabad, are described. In the analysis carried out in Cardiff, voltage-sensitive dyes that could detect the presence of viable cells were used on these air-samples. Clumps of viable cells were found to be present in samples collected at all the altitudes. The images obtained from electron microscopy are consistent with the above finding. Reference is also made to another paper presented at this conference describing the identification of bacterial species in the sample carried out in Sheffield. Counter arguments are discussed against the criticism that the detected cells and microorganisms (in the samples collected above the local tropopause at 16 km) are due to terrestrial contamination. This revised version was published online in August 2006 with corrections to the Cover Date.     

Processing of cometary grains at the nucleus surface

Cometary material inevitably undergoes chemical changes before and on leaving the nucleus. In seeking to explain comets as the origin of many IDPs (interplanetary dust particles), an understanding of potential surface chemistry is vital. Grains are formed and transformed at the nucleus surface; much of the cometary volatiles may arise from the organic material. In cometary near-surface permafrost, one expects cryogenic chemistry with crystal growth and isotope. This could be the hydrous environment where IDPs form. Seasonal and geographic variations imply a range of environmental conditions and surface evolution. Interplanetary dust impacts and electrostatic forces also have roles in generating cometary dust. The absence of predicted cometary dust ‘envelopes’ is compatible with the wide range of particle structures and compositions. Study of IDPs would distinguish between this model and alternatives that see comets as aggregates of core-mantle grains built in interstellar clouds.