Essam Heggy

Bio: Essam Heggy is an academic researcher from University of Southern California. The author has contributed to research in topics: Mars Exploration Program & Radar. The author has an hindex of 26, co-authored 149 publications receiving 3059 citations. Previous affiliations of Essam Heggy include University of Bordeaux & Lunar and Planetary Institute.

Radar Soundings of the Subsurface of Mars

Abstract: The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick.

Subsurface radar sounding of the south polar layered deposits of Mars.

Abstract: The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 x 10(6) cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick.

Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response

Abstract: The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed ∼100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements.

Properties of the 67P/Churyumov-Gerasimenko interior revealed by CONSERT radar

Abstract: The Philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus, providing information about its formation and evolution in the early solar system. We present Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) measurements of the interior of Comet 67P/Churyumov-Gerasimenko. From the propagation time and form of the signals, the upper part of the “head” of 67P is fairly homogeneous on a spatial scale of tens of meters. CONSERT also reduced the size of the uncertainty of Philae’s final landing site down to approximately 21 by 34 square meters. The average permittivity is about 1.27, suggesting that this region has a volumetric dust/ice ratio of 0.4 to 2.6 and a porosity of 75 to 85%. The dust component may be comparable to that of carbonaceous chondrites.

Depth of the Martian cryosphere: Revised estimates and implications for the existence and detection of subpermafrost groundwater

Abstract: [1] The Martian cryosphere is defined as that region of the crust where the temperature remains continuously below the freezing point of water. Previous estimates of its present thickness have ranged from ∼2.3–4.7 km at the equator to ∼6.5–12.5 km at the poles. Here we revisit these calculations, review some of the assumptions on which they were based, and investigate the effects of several parameters, not previously considered, on the cryosphere's thermal evolution and extent. These include astronomically driven climate change, the temperature-dependent thermal properties of an ice-rich crust, the potential presence of gas hydrate and perchlorate-saturated groundwater, and consideration of recent lower estimates of present-day global heat flow (which suggest a mean value roughly half that previously thought, effectively doubling the potential thickness of frozen ground). The implications of these findings for the continued survival of subpermafrost groundwater and its potential detection by the MARSIS radar sounder onboard Mars Express are then discussed. Although our estimates of the maximum potential thickness of the cryosphere have significantly increased, consideration of the likely range and spatial variability of crustal heat flow and thermal properties, in combination with the potential presence of potent freezing point depressing salts, may result in substantial local variations in cryosphere thickness. The locations that appear best suited for the detection of groundwater are those that combine low latitude (minimizing the thickness of frozen ground) and low elevation (minimizing the depth to a water table in hydrostatic equilibrium). Preliminary results from a MARSIS investigation of one such area are discussed.

Context Camera Investigation on board the Mars Reconnaissance Orbiter

Abstract: [1] The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government-furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt-type telescope of catadioptric optical design with a 5.7° field of view, providing a ∼30-km-wide swath from ∼290 km altitude; and a 5000-element CCD with a band pass of 500–700 nm and 7 μm pixels, giving ∼6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on-orbit experience. CTX has been allocated 12% of the total MRO data return, or about ≥3 terabits for the nominal mission. This data volume would cover ∼9% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.

Water on Mars

Abstract: Estimates of the amount of water outgassed from Mars, based on the composition of the atmosphere, range from 6 to 160 m, as compared with 3 km for the Earth. In contrast, large flood features, valley networks, and several indicators of ground ice suggest that at least 500 m of water have outgassed. The two sets of estimates may be reconciled if early in its history, Mars lost part of its atmosphere by impact erosion and hydrodynamic escape.

Integrated approach

Abstract: The Federal Aviation Administration (FAA), with its NextGen Air Transportation System (NextGen) and Performance-Based Navigation (PBN) initiatives, is moving towards a concept of integrated procedures implementation. Performance-Based Navigation initiatives include implementing Area Navigation (RNAV) and Required Navigation Performance (RNP) routes and procedures. The integrative concept of implementation of these procedures would mean a migration away from site by site (or runway by runway) procedure implementation process towards a NextGen readiness concept. This concept will include development of an integrated system of PBN routes and procedures by geographic area (incorporating metro areas and outlying airports). This concept delivers optimum benefits for the air traffic and carrier community. In addition, the integrative approach helps in prioritizing and formulating the funding requests to combine airspace, environmental, and procedures development. This paper discusses different aspects of this integrative approach.