Phobos and Mars orbit as a base for asteroid exploration and mining

We present the polarimetric measurements of the asteroid (16) Psyche for its whole rotational phase. Observations were conducted in the facilities of the OAN-SPM with a double beam polarizer (POLIMA 2) coupled to the 84 ​cm telescope in September 2019. Polarimetric lightcurves are valuable because they might provide useful information about the geometric albedo and surface properties of atmosphereless bodies.

The upcoming NASA mission to visit Psyche will verify most of the ground-based observations, however, there is a lack of polarimetric lightcurves, which could be useful for a more precise determination of the surface properties.

Polarimetry relies on relative flux variation of orthogonal polarization states to determine Stokes parameters. The aim, in this work, is to measure the amount of linearly polarized light reflected by the asteroid (16) Psyche.

The polarimetric lightcurve was obtained for a rotation period, and an amplitude of 0.14 ​± ​0.03% was measured for a phase angle of $∼17°$. From a comparison between the polarization curve with the corresponding photometric lightcurve, we found that the latter is possibly affected by both albedo and shape.

Our results show evidence of albedo variegation, which is in agreement with the albedo map of (16) Psyche obtained with different observational techniques.

The recent encounters with two C-type rubble-pile asteroids, Bennu and Ryugu, confirmed that their internal density was 1.2 $gc{m}^{−3}$, lower than the density of the previously explored S-type rubble pile Itokawa, 1.9 $gc{m}^{−3}$. As these are the only three rubble piles investigated in detail to date, little is known on how subtle differences in internal density of similarly shaped asteroids could affect surface slopes and thus downslope movement, particularly in near-Earth asteroids whose spin periods are affected by YORP. We modelled surface slopes for a range of internal densities and spin periods for seven small asteroid shape models to understand how differences in internal density of similarly shaped asteroids affect surface slope sensitivity to changes in spin period.

We found that for similarly shaped asteroids with spin periods under 6 to 8 h small differences in internal density can affect the slope sensitivity of different asteroids to changes in the spin period. Using the metric of 50% of the surface over 40° slope, as a proxy for catastrophic resurfacing, we found that for 6 of the 7 shape models catastrophic resurfacing would occur at $<$2.6 h for an internal density of 1.9 $gc{m}^{−3}$ compared to $<$3.2 h for an internal density of 1.2 $gc{m}^{−3}$. While this is not a large difference in spin periods, the result that lower density asteroids have surface slopes that are more sensitive to changes in the spin period suggests that low-density rubble piles (e.g. C-type) may have more evidence of downslope motion compared to similar shaped higher density rubble piles (e.g., S-type). The majority of the asteroid shape models investigated were spinning-tops, however, results from the Itokawa shape model hint that irregularly shaped asteroids are more sensitive to spin period changes than top-shaped asteroids, which may help explain why Itokawa has extensive lowlands compared to Ryugu and Bennu’s more rocky surfaces. Our study shows that for similarly shaped asteroids both density and spin periods are critical for determining surface stability and evolution.

Simple discrete and continuous gust models are presented for the lower atmosphere of Titan, for verification of the design of the Dragonfly rotorcraft. Models used for terrestrial airworthiness certification, essentially empirical in character, cannot be applied directly due to the different properties of Titan's atmosphere. The origins of terrestrial specifications are reviewed, and appropriate first-principles physical scalings are applied to the relevant parameters. A discrete ‘random-walk’ turbulence formulation is presented which offers simple implementation for numerical flight simulations. The model has applicability to other missions.

On Titan, liquid hydrocarbon may stay in the subsurface porous permeable crust known as the alkanofer, analogous to water in Earth's aquifer. In addition to pressure gradient, the subsurface liquid in alkanofers is subject to vertical compositional grading due to the gravity and temperature gradient. The common wisdom is that the liquid would normally stay underground in a stability established by the pressure that increases with depth as observed in aquifers on Earth. However, Titan's liquids consist of nitrogen and hydrocarbons, mainly methane and ethane, the behavior of which is very sensitive to temperature and pressure. Consequently, the liquid density does not always increase with depth, thus may introduce a reverse density profile that leads to vertical convective instability of the liquid column. If reverse density profiles are present, capillary pressures arising from liquid trapped within small pores in the crust can help with the column stability. The liquid held in the capillaries can seal the space below it thus helping with the stability, unless the overpressure built from underneath becomes larger than the capillary pressure, which causes leakage to allow the liquids to seep upward from the deep. This situation is analogous to hydrocarbon seeps on Earth, where oil and natural gas escape the reservoir and flow slowly through network of cracks to the surface. An algorithm based on an extended Gibbs equation commonly used in petroleum reservoir engineering is employed in this work to produce pressure, density, and compositional profiles for evaluating the stability and phase behavior of Titan's subsurface fluids.

We investigate the feasibility and demonstrate the merits of using Mars Orbiter Laser Altimeter (MOLA) profiles to retrieve seasonal height variations of CO₂ snow/ice cap in Mars’ polar areas by applying a co-registration strategy. We present a prototype analysis on the research region of [85.75°S, 86.25°S, 300°E, 330°E] that is located on the residual south polar cap. Our method comprises the recomputation of MOLA footprint coordinates with an updated Mars Global Surveyor (MGS) ephemeris and a revised Mars rotation model. The reprocessed MOLA dataset at the South Pole of Mars (poleward of 78°S) is then self-registered to form a coherent reference digital terrain model (DTM). We co-register segments of reprocessed MOLA profiles to the self-registered MOLA reference DTM to obtain the temporal height differences at either footprints or cross-overs. Subsequently, a two-step Regional Pseudo Cross-over Adjustment (RPCA) procedure is proposed and applied to post-correct the aforementioned temporal height differences for a temporal systematic bias and other residual errors. These pseudo cross-overs are formed by profile pairs that do not necessarily intersect, but are connected through the underlying DTM. Finally, CO₂ snow/ice temporal height variation is obtained by median-filtering those post-corrected temporal height differences. The precision of the derived height change time series is ∼4.7 ​cm. The peak-to-peak height variation is estimated to be ∼2 ​m. In addition, a pronounced â€?pitâ€? (transient height accumulation) of ∼0.5 ​m in magnitude centered at L_s ​= ​210° in southern spring is observed. The proposed method opens the possibility to map the seasonal CO₂ snow/ice height variations at the entire North and South polar regions of Mars.

The Active Seismic Experiments conducted during the Apollo 14 and 16 missions represented the first attempt to perform an off-Earth refraction seismic survey. The collected seismic traces have been analyzed by several authors and a two-layer structure has been suggested. The top layer consists of regolith, however the nature of the underlying material is still debated because the measured velocity is too low for a competent or even intensely fractured rock layer. Here we propose a new approach that combines refraction seismic and Ground Penetrating Radar (GPR) data to better constrain the underlying geological units. Given the relative uniformity of the shallow lunar subsurface and the interpretation of GPR data acquired at Von Kármán crater, we assumed that the second layer at the Apollo 14 and 16 landing sites is a mixture of fine materials and rocks. To assess this hypothesis we first reanalyzed the active seismic traces and computed the compressional wave velocities in the first and second layers, obtaining $v_0=116Â\pm 5m{s}^{−1}$ and $v_1=298Â\pm 52m{s}^{−1}$ at the Apollo 14 landing site and $v_0=122Â\pm 3m{s}^{−1}$ and $v_1=332Â\pm 23m{s}^{−1}$ at the Apollo 16 landing site. Second, we used a time-average model and laboratory data on the compressional wave velocity in lunar rocks to estimate the rock volume fraction that reproduces the overall compressional wave velocity in the second layer, with values ranging from 20 to 60% and 25 to 60% for the Apollo 14 and 16 landing sites, respectively. Finally, we used the rocks/fine materials ratio to estimate the overall dielectric constant of the second layer, which varies between 3.9 and 5.5. These results are in very good agreement with recent re-analysis of electromagnetic and seismic data collected at the Apollo 17 site and suggest that an ejecta deposit below the regolith might be common to all three sites.