The South Polar Terrain (SPT) of Enceladus is a site with eruptions of gas and water ice particle plumes, which indicate internal geodynamic activity. These eruptions are located along a series of tectonic structures, that is, the Tiger Stripe Fractures (TSF), which are composed of regularly spaced, linear depressions. The SPT is surrounded by sinuous chains of ridges and troughs (the Marginal Zone). To unravel the tectonics that affect the region and its evolution, we performed specific structural mapping and quantitative analyses of brittle features from remotely sensed images. The results are consistent with a block rotation model, in which several tectonic regimes coexist. The TSF are left‐lateral strike‐slip faults that bound rigid elongated blocks. The blocks rotate clockwise and are enclosed in a regional scale right‐lateral kinematic framework expressed in the Marginal Zone. These two opposite and complementary kinematic regimes induce transtensional and transpressional regimes within the SPT. An evolutionary tectonic model is proposed for the past and future evolution of the SPT. This model confirms the role of tectonic‐related kinematics in icy satellites and contributes to preparations for future missions.

Brittle deformation on Ganymede surface is represented by grooves tectonic linear landforms. These are regional scale structures that show well-defined morphology from straight to curvilinear. High density of grooves occupies most of the light terrain of the satellite, the grooved terrain. We map grooves on the USGS Voyager and Galileo Mosaic of Ganymede in order to unravel their spatial distribution and tectonic setting. A total of 14,707 grooves were identified, digitized and statistically analysed. A quantitative structural geology approach was used to classify grooves, by considering their azimuth and regional rotation. This procedure allowed to recognize a total of four groove families, named the NE, WNW, NW, and N-S super-systems. The presented structural map represents a tool to study the stress conditions associated with the groove formation and evolution. This map also aims to contribute to the scientific preparation of the upcoming missions and future exploration of Ganymede.

Aims. We provide a detailed analysis of different Phobos Mars Express/Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (MEX/OMEGA) visible and near-infrared (Vis-NIR) datacubes to understand the satellite blue-red spectral transition and its surface mineralogy while framing it within the debated satellite formation theories. Methods. We exploited three datacubes acquired in the 2004–2010 time frame. This dataset covers Phobos red and blue units located in the sub-Mars hemisphere at a scale ranging from 101 to 971 m/px. The OMEGA cubes were geometrically and photometrically corrected. We extracted the spectra in the 0.4–2.5 μm wavelength range from 11 different regions of interest (ROIs) located inside the Stickney crater and its closest surroundings as well as from Limtoc and Reldresal craters. Results. We detected a wide range of spectral variation within the Phobos surface not identified before. Besides the red and blue end-members, we observed a transitional colour change on the satellite sub-Mars hemisphere. We possibly identify a 2–7% absorption in the 0.7–1.3 μm spectral range only visible in the bluest area of the satellite. If real and not an instrument artefact, this would highlight the presence of a basaltic compound on the surface of Phobos. By comparing the OMEGA Vis-NIR extracted spectra with asteroid mean types, we were able to confirm the spectroscopic similarity between Phobos spectra and D-, T-type objects. Nevertheless, the reddest spectra observed on the Martian moon largely exceed even the D-type spectral slopes. Compared to several carbonaceous meteorites, the bluest satellite spectra show similar trends to the Cold Bokkeveld, Kaidun, and Murchison fusion crust. In contrast, the Vis-NIR trends of the Tagish Lake meteorite are more similar to some of the redder OMEGA spectra. As for the asteroid comparison, we find no match between the reddest Phobos spectra and primitive or dark meteorite samples.

Aims. We present a comparative visible and near-infrared multiband analysis of Phobos and Deimos aimed at characterising the compositional variability of the Martian moons. Methods. From multiband observations acquired by the Colour and Surface Stereo Imaging System (CaSSIS) on board on the ESA/ExoMars Trace Gas Orbiter (TGO), we analysed spectral ratios tracing ferric and ferrous minerals and mapped them over the surfaces of the Martian moons. We identified regions of interest (ROIs) on both moons and compare their mean spectra and spectral slopes. Results. We identified an overall similarity between the two Martian moons, whose variability can be explained by a different degree of ferric and ferrous mineralogy. In particular, the blue unit of Phobos can be explained by the presence of ferrous minerals, while the ferric minerals dominate in the red unit. We show that overall the Deimos surface matches the Phobos red units. On the contrary, the Deimos bright blue spots are spectrally similar to the Phobos transitional unit. We show the presence of a 1000 nm band only in the blue unit of Phobos. Conclusions. Our comparative multiband analysis of Phobos and Deimos is consistent with a similar composition of the two Moons, suggested by the spectral similarity of their redder units. The detection of an absorption towards 1000 nm in the blue unit suggests an exogenous nature of the latter.