No abstract

Minnaert and two-term phase function Hapke models are used to describe the photometric properties of the martian surface using HRSC (High Resolution Stereo Camera) multi-angular observations acquired along the ongoing Mars-Express mission. These observations can be pieced together to derive integrated phase functions over a wide range of phase angles. The photometric diversity at 675nm, as seen from orbit, of the martian surface properties across Gusev is depicted with seven units. Three photometric units widespread across the flanks of Apollinaris Patera flank and the floor of Gusev Crater are identified as having high single scattering albedo with rather forward scattering properties, low to intermediate macroscopic roughness and porous or not compacted powdered surface state as indicated by the opposition parameters. Another unit has the highest single scattering albedo, the smoothest surface in terms of macroscopic roughness, associated with an extremely forward scattering behavior. The opposition parameters are consistent with the presence of transparent particles in the surface powder layer. The distribution of this unit appears quite intermittent across the crater and does not seem to indicate any relationship with a given morphological structure. It may correspond to sparse areas where the structure of the surface dust layer is the most preserved. The most pronounced photometric changes are observed in three units associated with the low-albedo features corresponding to dark wind streaks. These units have a low single scattering albedo, are the most backscattering surfaces across Gusev, have a high surface roughness and present variable surface states as shown by the opposition parameters estimates, consistent with the occurrence of large grains organized in more or less packed layers. Clear differences are seen among these units in terms of opposition effect.

Very recently NASA astronauts took a new set of pictures from the International Space Station during night time in the frame of the NASA Crew Earth Observations program, giving a new opportunity to observe in color sprites and their parent lightning flashes. During about 20 h of observations, nondirectly dedicated to thunderstorm studies, 15 sprites were observed from August 2011 to April 2012. Chromatic observations allow analyzing thoroughly the main components of the sprite radiation. The red and green emissions, observed in all the sprite images, are due to the radiation of the first positive band system of molecular nitrogen N2. The blue emission, present in only 2 out of 15 sprites, is produced by the radiation of bands of the second positive band system of N2 and bands of the first negative band system of N2+ ions. It indicates the possible presence of ionization in these two sprites. The sprite brightness is equivalent to the Jupiter one.