An Overview Of The Origin Of Life: The Case For Biological Prospecting On Mars

Studies of the Earth's earliest biosphere have suggested a close coupling between the evolution of early life forms and the physical and chemical evolution of the planetary surface. From a biological perspective there were many similarities between early Earth and early Mars. This has led to the idea that an origin of life event may have occurred on Mars, leading to the development of microbial life. Various theories have been advanced to explain the origin of life on Earth, and these are reviewed with relevance to Mars. If traces of past or present biogenic activity are to be found on Mars, then the most likely place to prospect is several kilometers below the surface where liquid water might be stable. Such prospecting may best lend itself to human exploration. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Note on Turbulence Stationarity and Wind Persistence Within the Stable Planetary Boundary Layer

This note presents initial results of an analysis of the stationarity of turbulence kinetic energy and the persistence of winds within the stable boundary layer (SBL). Measurements were made at 1.5 and 11 m above ground level from 0100 to 0600 local time on five nights during the JORNADA field experiment. The average stationarity ranged from about 160 to about 570 s. Wind persistence ranged from about ± 40° (3-min average) to about ± 36° (30-min average) on a weakly stable night, and from about ± 40° (3-min average) to about ± 27° (30-min average) on an strongly stable night. It is shown that, at 1.5 m, which we take to be within the surface layer, the average duration of stationarity of turbulent kinetic energy tends to correlate with the kurtosis of the heat flux; however, at 11 m, which we take to be outside of the surface layer, this correlation is poorly approximated.     

Exobiological prospecting

Emma Newton , Howell G M Edwards , David Wynn-Williams and Julian A Hiscox review the combination of biology, geology and physics necessary to search for life off Earth.     

Near-source particulate emissions and plume dynamics from agricultural field operations

Particulate matter emissions generated by agricultural field preparation and harvesting operations were measured remotely via aerosol lidar and sampled simultaneously with a variety of aerosol point samplers in order to quantify dust plume space and time dynamics and particulate mass and number concentrations. Data for two cotton operations (disking, harvesting) in a flood-irrigated field in New Mexico are presented. Dust plume dynamics varied with boundary layer meteorological conditions, especially atmospheric stability, with plume maximum height significantly lower under stable conditions. Plume tracking indicated little change in plume area with height under unstable conditions and plume movement depended on wind speed and direction. Particle mass distributions indicate approximately 50% of the measured PM₁₀ mass was PM_2.5, significantly higher than previously reported values, possibly due to the near-source nature of the samples collected here. Variability in plume movement matched the variability in short-term wind fluctuations and this variability helps explain why models that utilize long-term averages perform poorly when trying to capture plume dynamics for nonsteady sources such as tractor operations.     

Wave-Modified Flux and Plume Dispersion in the Stable Boundary Layer

The effects of a pressure jump and a following internal gravity wave on turbulence and plume diffusion in the stable planetary boundary layer are examined. The pressure jump was accompanied by a sudden increase in turbulence and plume dispersion. The effects of wave perturbations on turbulence statistics are analysed by calculating fluxes and variances with and without the wave signal for averaging times ranging from 1 to 30 min. The wave signals are obtained using a band-pass filter. It is shown that second-order turbulence quantities calculated without first subtracting the wave perturbations from the time are greater than those calculated when the wave signal is separated from the turbulence. Estimates of the vertical dispersion of an elevated tracer plume in the stable boundary layer are made using an elastic backscatter lidar. Plume dispersion observed 25 m downwind of the source increases rapidly with the arrival of the flow disturbances. Measured plume dispersion and plume centreline height correlate with the standard deviation of the vertical velocity but not with the wave signal.     

Outer solar system, Europa, Titan and the possibility of life

A British Interplanetary Society Meeting brought together researchers on the varied environments on planets and moons that might harbour life, reports Julian Hiscox. The Jupiter and Saturn systems are especially dynamic and perhaps hold the key to how life originated on Earth.