Colin Wilson

Abstract:

[1] We present nightside observations of tropospheric carbon monoxide in the southern hemisphere near the 35 km height level, the first from Venus Express/Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)-M-IR. VIRTIS-M data from 2.18 to 2.50 μm, with a spectral resolution of 10 nm, were used in the analysis. Spectra were binned, with widths ranging from 5 to 30 spatial pixels, to increase the signal-to-noise ratio, while at the same time reducing the total number of retrievals required for complete spatial coverage. We calculate the mean abundance for carbon monoxide at the equator to be 23 ± 2 ppm. The CO concentration increases toward the poles, peaking at a latitude of approximately 60°S, with a mean value of 32 ± 2 ppm. This 40% equator-to-pole increase is consistent with the values found by Collard et al. (1993) from Galileo/NIMS observations. Observations suggest an overturning in this CO gradient past 60°S, declining to abundances seen in the midlatitudes. Zonal variability in this peak value has also been measured, varying on the order of 10% (∼3 ppm) at different longitudes on a latitude circle. The zonal variability of the CO abundance has possible implications for the lifetime of CO and its dynamics in the troposphere. This work has definitively established a distribution of tropospheric CO, which is consistent with a Hadley cell circulation, and placed limits on the latitudinal extent of the cell. Copyright 2008 by the American Geophysical Union.

Abstract:

Venus is the most Earthlike planet we know besides our own, in terms of its size and distance from its parent star. It was probably formed from the same materials as the Earth and Mars, at a similar time - why then has it become so different?To address this key question, a team of 170+ scientists from around the world formulated the European Venus Explorer (EVE) mission proposal to the European Space Agency's Cosmic Vision Programme in 2007. Although it was not chosen in the 2007 selection round for programmatic reasons, it was rated a high priority for the future European Space Science so we take this opportunity to reiterate the science goals which motivated the EVE mission, and to discuss the status of technological and programmatic developments required to address these goals.

Abstract:

A major limitation in the development of wind sensors for use on Mars is the lack of suitable testing and calibration facilities. A low-density wind tunnel has been developed at Oxford University for calibration of wind sensors for Mars landers, capable of providing stable or dynamically varying winds, of air or carbon dioxide, at Martian pressures (5-10 mbar) and speeds (0.5-30 m/s), and temperatures of 200-300 K. The flow field in the test section was calculated using analytical and computational modelling techniques, and validated experimentally using a pitot probe. This facility's stability and accuracy offer significant advantages with respect to previous calibration facilities. © 2008 Elsevier Ltd. All rights reserved.

Abstract:

We present zonal and meridional wind measurements at three altitude levels within the cloud layers of Venus from cloud tracking using images taken with the VIRTIS instrument on board Venus Express. At low latitudes, zonal winds in the Southern hemisphere are nearly constant with latitude with westward velocities of 105 ms^-1 at cloud-tops (altitude ∼ 66 km) and 60-70 ms^-1 at the cloud-base (altitude ∼ 47 km). At high latitudes, zonal wind speeds decrease linearly with latitude with no detectable vertical wind shear (values lower than 15 ms^-1), indicating the possibility of a vertically coherent vortex structure. Meridional winds at the cloud-tops are poleward with peak speed of 10 ms^-1 at 55° S but below the cloud tops and averaged over the South hemisphere are found to be smaller than 5 ms^-1. We also, report the detection at subpolar latitudes of wind variability due to the solar tide. Copyright 2008 by the American Geophysical Union.