Surface Properties of the Mars Science Laboratory Candidate Landing Sites: Characterization from Orbit and Predictions

This work describes the interpretation of THEMIS-derived thermal inertia data at the Eberswalde, Gale, Holden, and Mawrth Vallis Mars Science Laboratory (MSL) candidate landing sites and determines how thermophysical variations correspond to morphology and, when apparent, mineralogical diversity. At Eberswalde, the proportion of likely unconsolidated material relative to exposed bedrock or highly indurated surfaces controls the thermal inertia of a given region. At Gale, the majority of the landing site region has a moderate thermal inertia (250 to 410?J?m^?2?K^?1?s^?1/2), which is likely an indurated surface mixed with unconsolidated materials. The primary difference between higher and moderate thermal inertia surfaces may be due to the amount of mantling material present. Within the mound of stratified material in Gale, layers are distinguished in the thermal inertia data; the MSL rover could be traversing through materials that are both thermophysically and compositionally diverse. The majority of the Holden ellipse has a thermal inertia of 340 to 475?J?m^?2?K^?1?s^?1/2 and consists of bed forms with some consolidated material intermixed. Mawrth Vallis has a mean thermal inertia of 310?J?m^?2?K^?1?s^?1/2 and a wide variety of materials is present contributing to the moderate thermal inertia surfaces, including a mixture of bedrock, indurated surfaces, bed forms, and unconsolidated fines. Phyllosilicates have been identified at all four candidate landing sites, and these clay-bearing units typically have a similar thermal inertia value (400 to 500?J?m^?2?K^?1?s^?1/2), suggesting physical properties that are also similar.     

Mm wavelengths complex Doppler analysis using dark field illumination

Experimental results that indicate that at least two fundamental modes of Doppler generation are present when a rotating steel cylinder is broadside illuminated by radar. Improvised bistatic measurements at 77GHz are discussed and second order Doppler effects studied. Complex Doppler returns, consisting of two or more Doppler contributions, are decomposed and studied using empirical methods. In particular, ground illumination techniques are used to study Doppler in the shadow region of a cylinder of circumference 81 wavelengths. It is concluded that the complex Doppler response from the spinning cylinder consists of both direct (first order) and delayed (second order) Doppler components. Further measurements are proposed to study the delayed Doppler effect further.     

Dynamo Scaling Laws and Applications to the Planets

Scaling laws for planetary dynamos relate the characteristic magnetic field strength, characteristic flow velocity and other properties to primary quantities such as core size, rotation rate, electrical conductivity and heat flux. Many different scaling laws have been proposed, often relying on the assumption of a balance of Coriolis force and Lorentz force in the dynamo. Their theoretical foundation is reviewed. The advent of direct numerical simulations of planetary dynamos and the ability to perform them for a sufficiently wide range of control parameters allows to test the scaling laws. The results support a magnetic field scaling that is not based on a force balance, but on the energy flux available to balance ohmic dissipation. In its simplest form, it predicts a field strength that is independent of rotation rate and electrical conductivity and proportional to the cubic root of the available energy flux. However, rotation rate controls whether the magnetic field is dipolar or multipolar. Scaling laws for velocity, heat transfer and ohmic dissipation are also discussed. The predictions of the energy-based scaling law agree well with the observed field strength of Earth and Jupiter, but for other planets they are more difficult to test or special pleading is required to explain their field strength. The scaling law also explains the very high field strength of rapidly rotating low-mass stars, which supports its rather general validity.     

The quiet nighttime low-latitude ionosphere as observed by TIMED/GUVI

In this paper, we examine the nighttime ionosphere climatology structure in the low latitude region and discrepancies between Global Ultraviolet Imager (GUVI) observations and the IRI model predictions using (1) the magnetic zonal mean of electron number density as a function of altitude and magnetic latitude, (2) vertical electron density profiles at various levels of F10.7 index, (3) nighttime descent and magnitude decrease of the ionosphere, (4) point-to-point comparisons of F-peak height (hmF2) and density (NmF2), and (5) the magnetic longitudinal variations of hmF2 and NmF2. The data collected from the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission since its launch in December 2001 have provided great opportunities for many scientific investigations of the ionosphere. In this analysis, we investigate the climatology of the nighttime low-latitude ionosphere under low geomagnetic activity (kp ? 4) using the electron density profiles inferred from the airglow measurements obtained by the GUVI aboard the TIMED spacecraft and compared with the results obtained from IRI (International Reference Ionosphere) model-2001. The observed climatology is an essential tool for further understanding the electrodynamics in the low-latitude region and improving the model’s prediction capability. The time range of the GUVI data used in this study is from 2002 (day 053) to 2006 (day 304), and the IRI model predictions were produced at every GUVI location. The ionosphere observed is generally of greater density than what IRI predicts throughout the night for all four seasons for low and moderate solar activity while the model over-predicts the electron density near the F-region peak at high solar activity before midnight. Observations show that the height of the F-region peak has a steep descent from dusk to midnight and near midnight the height of layer is insensitive to solar conditions, significantly different than what is predicted by IRI. Longitudinal features shown in GUVI data are present in the low-latitude ionosphere after sunset and continue through to midnight after which the low-latitude ionosphere is largely zonally symmetric.     

Planetary Dynamos from a Solar Perspective

Direct numerical simulations of the geodynamo and other planetary dynamos have been successful in reproducing the observed magnetic fields. We first give an overview on the fundamental properties of planetary magnetism. We review the concepts and main results of planetary dynamo modeling, contrasting them with the solar dynamo. In planetary dynamos the density stratification plays no major role and the magnetic Reynolds number is low enough to allow a direct simulation of the magnetic induction process using microscopic values of the magnetic diffusivity. The small-scale turbulence of the flow cannot be resolved and is suppressed by assuming a viscosity far in excess of the microscopic value. Systematic parameter studies lead to scaling laws for the magnetic field strength or the flow velocity that are independent of viscosity, indicating that the models are in the same dynamical regime as the flow in planetary cores. Helical flow in convection columns that are aligned with the rotation axis play an important role for magnetic field generation and forms the basis for a macroscopic α-effect. Depending on the importance of inertial forces relative to rotational forces, either dynamos with a dominant axial dipole or with a small-scale multipolar magnetic field are found. Earth is predicted to lie close to the transition point between both classes, which may explain why the dipole undergoes reversals. Some models fit the properties of the geomagnetic field in terms of spatial power spectra, magnetic field morphology and details of the reversal behavior remarkably well. Magnetic field strength in the dipolar dynamo regime is controlled by the available power and found to be independent of rotation rate. Predictions for the dipole moment agree well with the observed field strength of Earth and Jupiter and moderately well for other planets. Dedicated dynamo models for Mercury, Saturn, Uranus and Neptune, which assume stably stratified layers above or below the dynamo region, can explain some of the unusual field properties of these planets.     

The Thermal Emission Imaging System (THEMIS) for the Mars 2001 Odyssey Mission

The Thermal Emission Imaging System (THEMIS) on 2001 Mars Odyssey will investigate the surface mineralogy and physical properties of Mars using multi-spectral thermal-infrared images in nine wavelengths centered from 6.8 to 14.9 μm, and visible/near-infrared images in five bands centered from 0.42 to 0.86 μm. THEMIS will map the entire planet in both day and night multi-spectral infrared images at 100-m per pixel resolution, 60% of the planet in one-band visible images at 18-m per pixel, and several percent of the planet in 5-band visible color. Most geologic materials, including carbonates, silicates, sulfates, phosphates, and hydroxides have strong fundamental vibrational absorption bands in the thermal-infrared spectral region that provide diagnostic information on mineral composition. The ability to identify a wide range of minerals allows key aqueous minerals, such as carbonates and hydrothermal silica, to be placed into their proper geologic context. The specific objectives of this investigation are to: (1) determine the mineralogy and petrology of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify future landing sites likely to represent these environments; (2) search for thermal anomalies associated with active sub-surface hydrothermal systems; (3) study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties; and (4) investigate polar cap processes at all seasons. THEMIS follows the Mars Global Surveyor Thermal Emission Spectrometer (TES) and Mars Orbiter Camera (MOC) experiments, providing substantially higher spatial resolution IR multi-spectral images to complement TES hyperspectral (143-band) global mapping, and regional visible imaging at scales intermediate between the Viking and MOC cameras. The THEMIS uses an uncooled microbolometer detector array for the IR focal plane. The optics consists of all-reflective, three-mirror anastigmat telescope with a 12-cm effective aperture and a speed of f/1.6. The IR and visible cameras share the optics and housing, but have independent power and data interfaces to the spacecraft. The IR focal plane has 320 cross-track pixels and 240 down-track pixels covered by 10 ～1-μm-bandwidth strip filters in nine different wavelengths. The visible camera has a 1024×1024 pixel array with 5 filters. The instrument weighs 11.2 kg, is 29 cm by 37 cm by 55 cm in size, and consumes an orbital average power of 14 W.     

The Emirates Mars Mission (EMM) Emirates Mars InfraRed Spectrometer (EMIRS) Instrument

Space Science Reviews - Modern observatories have revealed the ubiquitous presence of magnetohydrodynamic waves in the solar corona. The propagating waves (in contrast to the standing waves) are...     

The Student Dust Counter on the New Horizons Mission

The Student Dust Counter (SDC) experiment of the New Horizons Mission is an impact dust detector to map the spatial and size distribution of dust along the trajectory of the spacecraft across the solar system. The sensors are thin, permanently polarized polyvinylidene fluoride (PVDF) plastic films that generate an electrical signal when dust particles penetrate their surface. SDC is capable of detecting particles with masses m>10^?12 g, and it has a total sensitive surface area of about 0.1 m², pointing most of the time close to the ram direction of the spacecraft. SDC is part of the Education and Public Outreach (EPO) effort of this mission. The instrument was designed, built, tested, integrated, and now is operated by students.     

Planned Products of the Mars Structure Service for the InSight Mission to Mars

Space Science Reviews - The InSight lander will deliver geophysical instruments to Mars in 2018, including seismometers installed directly on the surface (Seismic Experiment for Interior Structure,...