The Dependence of Peak Electron Density on Solar Irradiance in the Ionosphere of Mars

National Aeronatics and Space Administration (NASA) (NNX08AN56G, NNX08AP96G, NNX12AJ39G

Development of software for analysing entry accelerometer data in preparation for the Beagle 2 mission to Mars: towards a publicly available toolkit

We have tested techniques for turning Beagle 2’s entry accelerometer data into a T(z) profile. We reproduced the PDS results for Pathfinder. The PDS trajectory for Pathfinder appears inconsistent with its entry state. Our code is available online

Should We Believe Atmospheric Temperatures Measured by Entry Accelerometers Traveling at "Slow" Near-Sonic Speeds?

Mars Pathfinder's Accelerometer instrument measured an unexpected and large temperature inversion between 10 and 20 kilometer altitude. Other instruments have failed to detect similar temperature inversions. I test whether this inversion is real or not by examining what changes have to be made to the assumptions in the accelerometer data processing to obtain a more "expected" temperature profile. Changes in derived temperature of up to 30K, or 15%, are necessary, which correspond to changes in derived density of up to 25% and changes in derived pressure of up to 10%. If the drag coefficient is changed to satisfy this, then instead of decreasing from 1.6 to 1.4 from 20 kilometers to 10 kilometers, the drag coefficient must increase from 1.6 to 1.8 instead. If winds are invoked, then speeds of 60 meters per second are necessary, four times greater than those predicted. Refinements to the equation of hydrostatic equilibrium modify the temperature profile by an order of magnitude less than the desired amount. Unrealistically large instrument drifts of 0.5-1.0 meters per square second are needed to adjust the temperature profile as desired. However, rotational contributions to the accelerations may have the necessary magnitude and direction to make this correction. Determining whether this hypothesis is true will require further study of the rigid body equations of motion, with detailed knowledge of the positions of all six accelerometers. The paradox concerning this inversion is not yet resolved. It is important to resolve it because the paradox has some startling implications. At one extreme, are temperature profiles derived from accelerometers inherently inaccurate by 20K or more? At the other extreme, are RS temperature profiles inaccurate by this same amount

Using Satellites to Probe Extrasolar Planet Formation

Planetary satellites are an integral part of the heirarchy of planetary systems. Here we make two predictions concerning their formation. First, primordial satellites, which have an array of distinguishing characteristics, form only around giant planets. If true, the size and duration of a planetary system's protostellar nebula, as well as the location of its snow line, can be constrained by knowing which of its planets possess primordial satellites and which do not. Second, all satellites around terrestrial planets form by impacts. If true, this greatly enhances the constraints that can be placed on the history of terrestrial planets by their satellites' compositions, sizes, and dynamics

Effects of Farming Practices on the Transfer of Phosphorus in Rural Catchments

To better understand the role of agriculture in the eutrophication of surface waters, the spatial and temporal variation in P concentrations in streams and storm runoff was examined in relation to historic and current farming practices (upland pasture improvement, soil P accumulation, soil cultivations and fertiliser and manure inputs) and other sources of P (farmyards, road runoff and wastewater discharge) in a number of small rural catchments in England. In an upland pasture catchment and a lowland mixed farming catchment, soil P was the major source of P export rather than annual field operations which generally did not coincide with the main periods of hydrological connectivity. The majority of P transfer was in particulate form (>0. 45 pm), although field plot investigations suggested this form of P was relatively insensitive to differences in soil P fertility as compared to the dissolved P fraction, and may release P to the watercolumn even at low soil P concentrations. Three mitigation options (early sowing, reduced cultivations and tramline removal) for reducing soil particulate P transfer were compared at the field scale. All three options had positive effects. Early crop establishment was the most effective, but not consistently so, suggesting a combination of measures is required on farms. Analysis of 118 storm runoff samples showed that farmyard and road runoff, and runoff receiving wastewater (septic tank) discharges were more concentrated in P than surface and sub-surface runoff from agricultural fields. These sources also arrive more continuously through the year and therefore are potentially more ecologically damaging than runoff from farmed land. It is concluded that urbanisation maybe a greater threat to eutrophication than agricultural intensification even in small rural catchments and that effective, integrated catchment management requires collective social responsibility to tackle the multiple sources of P entering water and not just the targeting of the farming community

The component structure of dense random subgraphs of the hypercube

Given $p \in (0,1)$, we let $Q_p= Q_p^d$ be the random subgraph of the $d$-dimensional hypercube $Q^d$ where edges are present independently with probability $p$. It is well known that, as $d \rightarrow \infty$, if $p>\frac12$ then with high probability $Q_p$ is connected; and if $p<\frac12$ then with high probability $Q_p$ consists of one giant component together with many smaller components which form the `fragment'. Here we fix $p \in (0,\frac12)$, and investigate the fragment, and how it sits inside the hypercube. In particular we give asymptotic estimates for the mean numbers of components in the fragment of each size, and describe their asymptotic distributions and indeed their joint distribution, much extending earlier work of Weber

Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment

Low-altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 +/- 4.8 km. The mean peak electron density in the meteoric layer is (1.33 +/- 0.25) x 10(10) m(-3). The mean width of the meteoric layer is 10.3 +/- 5.2 km. The occurrence rate of meteoric layers varies with season, solar zenith angle, and latitude. Seasonal variations in occurrence rate are particularly strong, often exceeding an order of magnitude. Meteoric layer altitude, peak electron density, and width are all positively correlated, with correlation coefficients of 0.3-0.4. Other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties, such as scale height, solar zenith angle, and solar flux, have absolute values that are significantly smaller, indicating lack of correlation. The photochemical lifetime of plasma in meteoric layers is similar to 12 days and depends on altitude