Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.

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[1] We used Mars Orbiter Laser Altimeter (MOLA) data from the current Mars Global Surveyor mission to characterize the topographic roughness of the Martian surface and to provide a mean to evaluate clutter at long (10-300 m) wavelengths. Such wavelengths are relevant for the MARSIS and SHARAD subsurface radars, which will be flown in future missions to Mars. The method of analysis is based on the assumption that topography can be described as a self-affine fractal: 30-km-long segments of MOLA altimetry profiles have thus been reduced to the topographic parameters RMS height, RMS slope, and Hurst exponent, this last related to the fractal dimension, which can be used as inputs to a near-nadir radar scattering model. The values of the Hurst exponent are greater than 0.5 for most of the surface, meaning a scaling behavior which is almost self-similar. Maps of RMS height and Hurst exponent show that these two parameters have very different spatial distributions: whereas the RMS height is patterned after the north-south dichotomy, the Hurst exponent follows a latitudinal trend. We make use of a multivariate method called G-mode to classify profiles in the three-dimensional parameter space: we find several roughness units, some of which have a strong correlation with certain geologic units, while others are bound by latitude. However, at scales between 300 m and 3 km, large stretches of the surface of Mars share common statistical properties of topography, independent from the north-south dichotomy.

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The paper describes the Rosetta Lander named Philae and introduces its complement of scientific instruments. Philae was launched aboard the European Space Agency Rosetta spacecraft on 02 March 2004 and is expected to land and operate on the nucleus of 67P/Churyumov-Gerasimenko at a distance of about 3 AU from the Sun. Its overall mass is ∼98 kg (plus the support systems remaining on the Orbiter), including its scientific payload of ∼27 kg. It will operate autonomously, using the Rosetta Orbiter as a communication relay to Earth. The scientific goals of its experiments focus on elemental, isotopic, molecular and mineralogical composition of the cometary material, the characterization of physical properties of the surface and subsurface material, the large-scale structure and the magnetic and plasma environment of the nucleus. In particular, surface and sub-surface samples will be acquired and sequentially analyzed by a suite of instruments. Measurements will be performed primarily during descent and along the first five days following touch-down. Philae is designed to also operate on a long time-scale, to monitor the evolution of the nucleus properties. Philae is a very integrated project at system, science and management levels, provided by an international consortium. The Philae experiments have the potential of providing unique scientific outcomes, complementing by in situ ground truth the Rosetta Orbiter investigations.