The natural modes of Ontario Lacus surface oscillations, the largest lake in Titan’s southern hemisphere, are simulated and analyzed as they are potentially of broad interest in a variety of dynamical researches. We found that tidal forces are too low in frequency to excite the (barotropic) normal modes. Broadband wind forcing likely spans the resonant frequencies. High wind speed, which could be encountered under episodic phenomena such as storms, would be required to significantly excite the normal modes. While the slower baroclinic normal modes could more easily be resonantly forced by the low-frequency tidal forces, addressing this issue demands unavailable information about the lake stratification.@en

The aim of this paper is to present the concept of a dedicated gravity field mission for the planet Mars, the Mars Quantum Gravity Mission (MaQuIs). The mission is targeted at improving the data on the gravitational field of Mars, enabling studies on planetary dynamics, seasonal changes, and subsurface water reservoirs. MaQuIs follows well known mission scenarios, currently deployed for Earth, and includes state-of-the-art quantum technologies to enhance the gained scientific signal.@en

In the context of the emergence of extraterrestrial oceanography, we adapted an existing oceanographic model, SLIM (www.climate.be/slim), to the conditions of Titan, a moon of Saturn. The tidal response of the largest southern lake at Titan’s surface, namely Ontario Lacus, is simulated. SLIM solves the 2D, depth-averaged shallow water equations on an unstructured mesh using the discontinuous Galerkin finite element method, which allows for high spatial resolution wherever needed. The impact of the wind forcing, the bathymetry, and the bottom friction is also discussed. The predicted maximum tidal range is about 0.56 m in the southern part of the lake, which is more than twice as large as the previous estimates (see Tokano, Ocean Dyn 60:(4) 803–817 doi:10.1007/s10236-010-0285-3 2010). The patterns and magnitude of the current are also markedly different from those of previous studies: the tidal motion is not aligned with the major axis of the lake and the speed is larger nearshore. Indeed, the main tidal component rotates clockwise in an exact period of one Titan day and the tidal currents can reach 0.046 ms−1 close to the shores depending on the geometry and the bathymetry. Except for these specific nearshore regions, the current speed is less than 0.02 ms−1. Circular patterns can be observed offshore, their rotational direction and size varying along the day.@en

Small body missions can significantly benefit from deploying small landing systems onto the surface of the visited object. Despite the potential benefit that they may bring, deployments of landers in small body environments may entail significant mission design challenges. This paper thus addresses the potential of ballistic landing opportunities in binary asteroid moons from a mission design perspective, particularly focusing on reliability aspects of the trajectories. Two binaries that were previously identified as target bodies in several missions/proposals, Didymos and 1996 FG3, are considered in this paper. The dynamics near them are modeled by means of the Circular Restricted Three Body Problem (CR3BP), which provides a reasonable representation of a standard binary system. Natural landing trajectories that allow both minimum-velocity local-vertical touchdown and deployment from a safe distance are investigated. Coefficient of restitution values are used as a design parameter to compute the first touchdown speeds that ensure sufficient reliability of landing trajectories. A simple reliability index, which is derived via uncertainty ellipsoid from covariance analysis, is introduced to create a global reliability map across the asteroid surfaces. Assuming 3σ deployment errors on the order of 90 m and 2 cm/s, the results show that ballistic landing operations are likely to be successful for larger binary moons if the deployments target near equatorial regions within longitude range 320 o –20°. It has also been shown that the deployments to smaller binary moons may require higher accuracy in navigation and deployment systems in their mothership, and/or closer deployment distances.@en

The tidal response of Titan's two largest northern seas, Ligeia Mare and Kraken Mare, is studied by means of a two-dimensional, depth-averaged, shallow water model, SLIM (http://www.climate.be/slim). Kraken Mare is formed of two basins, the northern one being assumed to be linked by a single strait, Trevize Fretum, to Ligeia Mare. The tidal motions tend to be independent of each other in each basin (i.e., Ligeia Mare, Kraken 1 and Kraken 2) which results in sharp transitions in the straits. Our results are overall rather similar to those of Tokano et al. (2014), suggesting that a 2D model such as SLIM is adequate for modelling Titan's tides and, since it is (presumably) less computationally demanding, may be better for sensitivity studies. For instance, the maximum tidal range in Kraken and Ligeia Maria respectively are 0.29 m and 0.14 m, which is within the range predicted by Lorenz et al. (2014) although smaller by 0.07 m and larger by 0.04 m than the estimates of Tokano et al. (2014) (but it occurs at the same location). The tidal currents are faster (by about one order of magnitude) in the straits linking those Maria than in the basins themselves (with a maximum of 0.36 m/s in the strait linking Kraken 1 and Kraken 2, Seldon Fretum). A decomposition of the tidal history into different harmonic components is carried out. Except in specific areas such as the straits and the amphidromic point(s), the main tidal component has a period of 1 Titan Day. We also briefly studied the eigenmodes of the northern seas whose period is close to the tidal period: such modes are very local. Indeed, their magnitude is significant (with respect to the magnitude of the modes elsewhere in the seas) in small bay(s) or near the islands of Kraken 2 and Ligeia Mare. They are not excited by the tides as they do not appear in the tidal motion.A sensitivity analysis to poorly constrained parameters (bottom friction coefficient, depth of Trevize Fretum and attenuation factor - the latter is briefly discussed with respect to the values of the Love numbers found in the literature) is also conducted. The model parameters are seen to have a significant impact on the liquid exchanges between the basins and, consequently, on the tidal range and phase, fluid velocity and location of amphidromic point(s).@en

The tidal response of Titan's two largest northern seas, Ligeia Mare and Kraken Mare, is studied by means of a two-dimensional, depth-averaged, shallow water model, SLIM (http://www.climate.be/slim). Kraken Mare is formed of two basins, the northern one being assumed to be linked by a single strait, Trevize Fretum, to Ligeia Mare. The tidal motions tend to be independent of each other in each basin (i.e., Ligeia Mare, Kraken 1 and Kraken 2) which results in sharp transitions in the straits. Our results are overall rather similar to those of Tokano et al. (2014), suggesting that a 2D model such as SLIM is adequate for modelling Titan's tides and, since it is (presumably) less computationally demanding, may be better for sensitivity studies. For instance, the maximum tidal range in Kraken and Ligeia Maria respectively are 0.29 m and 0.14 m, which is within the range predicted by Lorenz et al. (2014) although smaller by 0.07 m and larger by 0.04 m than the estimates of Tokano et al. (2014) (but it occurs at the same location). The tidal currents are faster (by about one order of magnitude) in the straits linking those Maria than in the basins themselves (with a maximum of 0.36 m/s in the strait linking Kraken 1 and Kraken 2, Seldon Fretum). A decomposition of the tidal history into different harmonic components is carried out. Except in specific areas such as the straits and the amphidromic point(s), the main tidal component has a period of 1 Titan Day. We also briefly studied the eigenmodes of the northern seas whose period is close to the tidal period: such modes are very local. Indeed, their magnitude is significant (with respect to the magnitude of the modes elsewhere in the seas) in small bay(s) or near the islands of Kraken 2 and Ligeia Mare. They are not excited by the tides as they do not appear in the tidal motion.A sensitivity analysis to poorly constrained parameters (bottom friction coefficient, depth of Trevize Fretum and attenuation factor - the latter is briefly discussed with respect to the values of the Love numbers found in the literature) is also conducted. The model parameters are seen to have a significant impact on the liquid exchanges between the basins and, consequently, on the tidal range and phase, fluid velocity and location of amphidromic point(s).@en