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Michael T Mellon - One of the best experts on this subject based on the ideXlab platform.
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Apparent Thermal Inertia and the surface heterogeneity of Mars
Icarus, 2007Co-Authors: Nathaniel E. Putzig, Michael T MellonAbstract:Abstract Thermal Inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters. Consequently, surfaces with horizontal or vertical heterogeneity may yield apparent Thermal Inertia which varies with time of day and season. To investigate these temporal variations, we processed three Mars years of Mars Global Surveyor Thermal Emission Spectrometer observations and produced global nightside and dayside seasonal maps of apparent Thermal Inertia. These maps show broad regions with diurnal and seasonal differences up to 200 J m −2 K −1 s −1/2 at mid-latitudes (60° S to 60° N) and 600 J m −2 K −1 s −1/2 or greater in the polar regions. We compared the seasonal mapping results with modeled apparent Thermal Inertia and created new maps of surface heterogeneity at 5° resolution, delineating regions that have Thermal characteristics consistent with horizontal mixtures or layers of two materials. The Thermal behavior of most regions on Mars appears to be dominated by layering, with upper layers of higher Thermal Inertia (e.g., duricrusts or desert pavements over fines) prevailing in mid-latitudes and upper layers of lower Thermal Inertia (e.g., dust-covered rock, soils with an ice table at shallow depths) prevailing in polar regions. Less common are regions dominated by horizontal mixtures, such as those containing differing proportions of rocks, sand, dust, and duricrust or surfaces with divergent local slopes. Other regions show Thermal behavior that is more complex and not well-represented by two-component surface models. These results have important implications for Mars surface geology, climate modeling, landing-site selection, and other endeavors that employ Thermal Inertia as a tool for characterizing surface properties.
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The Apparent Thermal Inertia of Layered Surfaces on Mars
2007Co-Authors: Michael T Mellon, Nathaniel E. PutzigAbstract:Introduction: Thermal Inertia is the key surface property that controls the temperature response of the martian surface to solar heating. It is defined as square root of the product of the Thermal conductivity, density and heat capacity. Visible and infrared spectroscopy senses the material composition of the upper microns to tens of microns of the surface. Visible imaging exposes the physical structure of the surface and subsurface at typically meter to kilometer scales, at comparable vertical and horizontal scales. Thermal Inertia provides a window into the physical and compositional structure of the surface at an intermediate depth scale of few centimeters to a few decimeters. The Thermal Inertia of the martian surface has been derived over the last several decades from numerous remote sensing observations of the instantaneous surface temperature [e.g. Kieffer et al., 1977; Mellon et al., 2000]. Inherent in the various methods employed for deriving Thermal Inertia from these observations is the assumption that the subsurface (the upper centimeters to meters) consists of homogeneous soil. Real surface soils are rarely homogeneous, exhibiting of structural and compositional layers or complex three dimensional clastic matrices. However, in the absence of a priori knowledge of the subsurface structure, the homogeneous assumption has been employed and an apparent Thermal Inertia derived. In this work we examine the effects of layering in the martian subsurface on the diurnal and seasonal surface temperatures, and on the apparent Thermal Inertia as has been derived assuming homogeneity. By understanding the Thermal signature of layered surfaces we can ultimately determine their distribution on Mars, improve our ability to interpret Thermal Inertia data, and better understand the structure of the martian surface and shallow subsurface. Geologic settings for martian surfaces: We examine several example types of natural layering that may exist on Mars based on terrestrial analogs, or do occur on the surface of Mars based on landed observations [e.g., Mutch et al., 1977; Binder et al., 1977; Ward et al., 1999; Squyres et al., 2004a; 2004b]. Differences in composition or physical makeup of the different layers can result in large Thermal Inertia contrasts by nearly two orders of magnitude (see Table 1). These Thermal Inertia contrasts will result in distinct temperature and apparent Thermal Inertia behaviors. Many areas of the surface of Mars are dominated by low Thermal Inertia dust. Lander observations have revealed that dust settling from the atmosphere is ubiquitous. Atmospheric dust coats solar panels and other spacecraft components. Dust has been observed to coat surface rocks, particularly on top of rocks, as well as coarser soils. Ice rich permafrost is believed to be common at high latitudes on Mars in both hemispheres [Leighton and Murray 1966; Boynton et al. 2002]. Models of subsurface-ice stability have long suggested shallow ground ice will persist in the current martian climate beneath a veneer of dry, ice-free soil, perhaps as shallow as centimeters below the surface [Mellon et al., 2004]. Indeed, observations of neutron and gamma ray flux support this view of a layered permafrost with ice just centimeters below the surface in some locations. Ice-cemented soil exhibits a Thermal Inertia comparable to that of rock. Duricrusts, weakly salt-cemented soils, are also observed at every landing site. These crusts are typically observed in shallow excavations, and exhibit a layered character with crusted soils overlying unconsolidated soils. A cemented layer in an otherwise homogeneous soil will exhibit dramatically different Thermal properties, even if the cementing agent is low in abundance. Desert pavements are another example of a layered surface material, where larger particles accumulate at the surface due to aeolian deflation (and frost heave in cold climates). Pavements are common in terrestrial polar and non-polar desert regions forming an armor of interlocking cobbles or layers of coarse soil grains over an otherwise fine grained soil matrix. Similar particle size sorting and layering has been observed at some landing sites [e.g. Arvidson et al., 2004]. These geologic settings provide examples of thermophysical characteristics of lower-Thermal-Inertia material overlaying higher-Thermal-Inertia material (dust coatings and permafrost layers), or conversely higher-Thermal-Inertia material over lower-ThermalInertia material (duricrust and desert pavement). In practice, a wide range of geologic configurations can be envisioned and represented by these examples.
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Effects of Surface Heterogeneity on the Apparent Thermal Inertia of Mars
2006Co-Authors: Nathaniel E. Putzig, Michael T MellonAbstract:Introduction: Using a modified version of the algorithm described in Mellon et al. (2000) [1], we derived Thermal Inertia from three Mars years of brightness temperature observations by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES). Global mapping results show seasonal and diurnal differences in apparent Thermal Inertia as large as 200-600 J m-2 K-1 s-! (units hereinafter assumed) or more over most of the surface. In this work we focus on examining potential root causes for these variations and their implications for the surface characteristics of Mars. Current methods [1,2] for deriving Thermal Inertia generally assume that surface properties are horizontally and vertically uniform on the scale of the instrument’s observational footprint and sensing depth. Due to the nonlinear relationship between temperature and Thermal Inertia, sub-pixel horizontal heterogeneity or near-surface layering may yield different apparent Thermal Inertia values at different seasons or times of day. Additional modifications of the Thermal model and algorithm were undertaken to characterize the expected Thermal behavior of idealized mixed and layered surfaces. Comparison of the modeling results with the TES-derived mapping results indicates that much of the martian surface may be dominated by (1) horizontally mixed surfaces, such as those containing differing proportions of rocks, sand, dust, and duricrust; (2) lower Thermal Inertia layers over higher Thermal Inertia substrates, such as dust over rocks or dry soils over an ice table at depth; and (3) higher Thermal Inertia layers over lower Thermal Inertia substrates, such as duricrust or desert pavements over relatively unconsolidated finer materials. Background: The Thermal behavior of the martian surface can be represented as a boundary condition on the Thermal diffusion equation, where radiative loss to space is balanced by subsurface conduction and heat flux due to insolation (FSUN), down-welling atmospheric radiation (FIR), and seasonal CO2 condensation (FCO2):
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Global Thermal Inertia and surface properties of Mars from the MGS mapping mission
Icarus, 2005Co-Authors: Nathaniel E. Putzig, Katherine A. Kretke, Michael T Mellon, Raymond E. ArvidsonAbstract:Abstract We present a new high-resolution map of Thermal Inertia derived from observations of planetary brightness temperature by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) obtained during the entire MGS primary mapping mission. Complete seasonal coverage provides a nearly global view of Mars, including the polar regions, at a spatial resolution of approximately 3 km. Our map of nighttime Thermal-bolometer-based Thermal Inertia covers approximately 60% of the surface between 80° S and 80° N latitudes. We confirm the global pattern of high and low Thermal Inertia seen in lower resolution mapping efforts and provide greater detail concerning a third surface unit with intermediate values of both Thermal Inertia and albedo first identified by Mellon et al. 2000, Icarus 148, 437–455. Several smaller regional units with distinct characteristics are observed. Most notably, a unit of low Thermal Inertia ( 175 J m −2 K −1 s − 1 / 2 ) and low-to-intermediate albedo (0.09–0.22) dominates the region polewards of 65° S. We consider possible causes for these characteristics and conclude that a low-density mantle formed by desiccation of a previously ice-rich near-surface layer is the most likely explanation for the observed thermophysical properties. Global comparison of Thermal Inertia and elevation shows that high and low Thermal Inertia values can be found over a broad range of elevation, with only low values (30– 130 J m −2 K −1 s − 1 / 2 ) occurring at the highest elevations and the highest values occurring only at lower elevations. However, the lowest values ( 30 J m −2 K −1 s − 1 / 2 ) are found only at lower elevations, implying that the distribution of low Thermal Inertia material is not solely controlled by atmospheric pressure and the trapping of fines at high elevations. A new estimate of Thermal Inertia for the Viking and Pathfinder landing sites helps establish an important link between surface characteristics observed in situ and those derived from remote-sensing data.
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high resolution Thermal Inertia mapping of mars sites of exobiological interest
Journal of Geophysical Research, 2001Co-Authors: Bruce M. Jakosky, Michael T MellonAbstract:We have mapped Thermal Inertia at high resolution for selected regions of Mars that are of potential biological relevance, using observations made by the Mars Global Surveyor Thermal Emission Spectrometer. Thermal Inertia is a direct indicator of physical properties of the surface at the decimeter-to-meter scale. Our goal is to understand the geological processes by which the sites formed and their subsequent evolution, their current state, and their safety and science potential as landing sites for future lander, rover, and sample-return spacecraft missions. The Thermal Inertia values at ∼3-km scale for the sites considered span the entire range of values measured at Mars; Thermal Inertias range from low values indicative of substantial aeolian mantling up to high values suggesting surfaces covered predominantly with bedrock, exposed rocks or blocks, or well-indurated crusts. The highest Thermal Inertias correlate strongly with local morphology, while areas with intermediate and low Thermal Inertias generally show no such correlation. This suggests that selection of future landing sites will be plagued by a choice of a well-mantled site that is safe but less interesting scientifically versus an unmantled site that is more interesting scientifically but less safe.
Michael Mueller - One of the best experts on this subject based on the ideXlab platform.
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Thermal Inertia of eclipsing binary asteroids: the role of component shape
2015Co-Authors: Michael Mueller, Marlies Van De WeijgaertAbstract:Thermal Inertia controls the temperature distribution on asteroid surfaces. This is of crucial importance to the Yarkovsky effect and for the planning of spacecraft operations on or near the surface. Additionally, Thermal Inertia is a sensitive indicator for regolith structure.A uniquely direct way of measuring Thermal Inertia is through observations of the Thermal response to an eclipse in a binary system, when one component shadows the other. This method was pioneered by Mueller et al. (2010), who observed eclipses in (617) Patroclus using Spitzer IRS. Buie et al. (2015) report observations of a stellar occultation by Patroclus. Their estimate for the system's projected size agrees well with the Spitzer result. However, the occultation revealed that the components are much more oblately shaped than was assumed by Mueller et al.This prompted us to study the role of component shape in the analysis of Thermal eclipse data. Conceivably, the global shape can have a significant impact on the shape and size of the eclipsed area and therefore on its Thermal emission. So far, this has not been studied in a systematic way. Using Patroclus and the existing Spitzer data as our test case, we vary the ellipsoidal component shape and determine the resulting best-fit Thermal Inertia. This will lead to an updated estimate of Patroclus' Thermal Inertia, along with a potentially more realistic estimate of its uncertainty. Beyond that, our results will inform ongoing and future Thermal studies of other eclipsing binary asteroids.
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Eclipsing Binary Trojan Asteroid Patroclus: Thermal Inertia from Spitzer Observations
Icarus, 2010Co-Authors: Michael Mueller, Daniel Hestroffer, Jérôme Berthier, Stefano Mottola, Alan W. Harris, Joshua P. Emery, Franck Marchis, Mario Di MartinoAbstract:We present mid-infrared (8-33 micron) observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope.F or the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the Thermal Inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system's known mutual orbit, arbitrary component shapes, and Thermal conduction in the presence of eclipses. We obtain two local Thermal-Inertia values, representative of the respective shadowed areas: 21+/14 MKS and 6.4+/-1.6 MKS. The average Thermal Inertia is estimated to be 20+/-15 MKS, potentially with significant surface heterogeneity. This first Thermal-Inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and 98+/-10 km, respectively, in agreement with previous findings. Taken together with the system's known total mass, this implies a bulk mass density of 1.08 +/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice.
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Eclipsing binary Trojan asteroid Patroclus: Thermal Inertia from Spitzer observations
Icarus, 2010Co-Authors: Michael Mueller, Daniel Hestroffer, Jérôme Berthier, Stefano Mottola, Alan W. Harris, Joshua P. Emery, Franck Marchis, Mario Di MartinoAbstract:48 pages, 6 tables, 5 figures. The original publication is available in Icarus (www.elsevier.com/locate/icarus).International audienceWe present mid-infrared (8-33 micron) observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope.F or the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the Thermal Inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system's known mutual orbit, arbitrary component shapes, and Thermal conduction in the presence of eclipses. We obtain two local Thermal-Inertia values, representative of the respective shadowed areas: 21+/14 MKS and 6.4+/-1.6 MKS. The average Thermal Inertia is estimated to be 20+/-15 MKS, potentially with significant surface heterogeneity. This first Thermal-Inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and 98+/-10 km, respectively, in agreement with previous findings. Taken together with the system's known total mass, this implies a bulk mass density of 1.08 +/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice
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Thermal Inertia of near-Earth Asteroids and Strength of the Yarkovsky Effect
Bulletin of the American Astronomical Society, 2006Co-Authors: Marco Delbo, Aldo Dell'oro, Stefano Mottola, Alan W. Harris, Michael MuellerAbstract:Thermal Inertia is the physical parameter that controls the temperature distribution over the surface of an asteroid. It affects the strength of the Yarkovsky effect, which causes orbital drift of km-sized asteroids and is invoked to explain the delivery of near-Earth asteroids (NEAs) from the main belt. Moreover, measurements of Thermal Inertia provide information on the presence or absence of loose surface material, such as Thermally insulating regolith or dust. At present, very little is known about the Thermal Inertia of asteroids in the km size range. Using an extensive dataset of Thermal infrared observations obtained at the Keck 1, the ESO 3.6m and the IRTF telescopes, we find that the mean Thermal Inertia of near-Earth asteroids in the km-size range is 200 ± 50 J m-2 s-0.5 K-1 corresponding to a surface Thermal conductivity of 0.03 ± 0.01 W m-1K-1. Combining this result with published values of asteroid Thermal Inertias, we also identify a trend of increasing Thermal Inertia with decreasing asteroid size. As a consequence, the dependence of the Yarkovsky-induced semimajor axis drift rate on object diameter, D, departs from the 1/D dependence commonly assumed in models of the dynamical evolution of asteroids.
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Thermal Inertia of Near-Earth Asteroids and Magnitude of the Yarkovsky Effect
2006Co-Authors: Marco Delbo, Aldo Dell'oro, Stefano Mottola, Alan W. Harris, Michael MuellerAbstract:Thermal Inertia of near-Earth asteroids and magnitude of the Yarkovsky effect M. Delbo* (1,2), A. Dell'Oro (2), A. W. Harris (3), S. Mottola (3), M. Mueller (3) (1) Observatoire de la Cote d'Azur B.P. 4229, 06034 Nice Cedex 4, France. (2) INAF-Osservatorio Astr. di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy. (3) DLR Institute of Planetary Research, Rutherfordstrasse 2, 12489 Berlin, Germany. Thermal Inertia is the physical parameter that controls the temperature distribution over the surface of an asteroid. It affects the strength of the Yarkovsky effect, which causes orbital drift of km-sized asteroids and is invoked to explain the delivery of near-Earth asteroids (NEAs) from the main belt. Measurements of Thermal Inertia provide information on the presence or absence of loose surface material, such as Thermally insulating regolith or dust. Such information is not only important for scientific studies of asteroid surface properties, but it is also vital for the design of lander missions and in the development of technology for the deflection of hazardous asteroids. At present, very little is known about the Thermal Inertia of asteroids in the km size range. Here we report on a method that has allowed us to derive a mean value for the Thermal Inertia of near-Earth asteroids on the basis of multi-wavelength Thermal-infrared observations. We obtain a mean value of 200 ± 50 J m-2 s-0.5 K -1 corresponding to a surface Thermal conductivity of 0.03 ± 0.01 W m-1 K-1 . We also identify a trend of increasing Thermal Inertia with decreasing asteroid size. As a consequence, the dependence of the Yarkovsky-induced semimajor axis drift rate on object diameter, D, departs from the 1/D dependence commonly assumed in models of the dynamical evolution of asteroids. *The work of Marco Delbo has been partially supported by the European Space Agency (ESA).
Mario Di Martino - One of the best experts on this subject based on the ideXlab platform.
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Eclipsing Binary Trojan Asteroid Patroclus: Thermal Inertia from Spitzer Observations
Icarus, 2010Co-Authors: Michael Mueller, Daniel Hestroffer, Jérôme Berthier, Stefano Mottola, Alan W. Harris, Joshua P. Emery, Franck Marchis, Mario Di MartinoAbstract:We present mid-infrared (8-33 micron) observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope.F or the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the Thermal Inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system's known mutual orbit, arbitrary component shapes, and Thermal conduction in the presence of eclipses. We obtain two local Thermal-Inertia values, representative of the respective shadowed areas: 21+/14 MKS and 6.4+/-1.6 MKS. The average Thermal Inertia is estimated to be 20+/-15 MKS, potentially with significant surface heterogeneity. This first Thermal-Inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and 98+/-10 km, respectively, in agreement with previous findings. Taken together with the system's known total mass, this implies a bulk mass density of 1.08 +/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice.
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Eclipsing binary Trojan asteroid Patroclus: Thermal Inertia from Spitzer observations
Icarus, 2010Co-Authors: Michael Mueller, Daniel Hestroffer, Jérôme Berthier, Stefano Mottola, Alan W. Harris, Joshua P. Emery, Franck Marchis, Mario Di MartinoAbstract:48 pages, 6 tables, 5 figures. The original publication is available in Icarus (www.elsevier.com/locate/icarus).International audienceWe present mid-infrared (8-33 micron) observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope.F or the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the Thermal Inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system's known mutual orbit, arbitrary component shapes, and Thermal conduction in the presence of eclipses. We obtain two local Thermal-Inertia values, representative of the respective shadowed areas: 21+/14 MKS and 6.4+/-1.6 MKS. The average Thermal Inertia is estimated to be 20+/-15 MKS, potentially with significant surface heterogeneity. This first Thermal-Inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and 98+/-10 km, respectively, in agreement with previous findings. Taken together with the system's known total mass, this implies a bulk mass density of 1.08 +/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice
Hugh H Kieffer - One of the best experts on this subject based on the ideXlab platform.
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High‐resolution Thermal Inertia derived from the Thermal Emission Imaging System (THEMIS): Thermal model and applications
Journal of Geophysical Research, 2006Co-Authors: Robin L. Fergason, Philip R Christensen, Hugh H KiefferAbstract:[1] Thermal Inertia values at 100 m per pixel are determined using nighttime temperature data from the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft, producing the highest-resolution Thermal Inertia data set to date. THEMIS Thermal Inertia values have an overall accuracy of ∼20%, a precision of 10–15%, and are consistent with both Thermal Emission Spectrometer orbital and Miniature Thermal Emission Spectrometer surface Thermal Inertia values. This data set enables the improved quantification of fine-scale surface details observed in high-resolution visible images. In the Tharsis region, surface textures and crater rims observed in visible images have no corresponding variation in the THEMIS Thermal Inertia images, indicating that the dust mantle is pervasive at THEMIS scales and is a minimum of a few centimeters and up to 1–2 m thick. The Thermal Inertia of bed form material indicates particle diameters expected for aeolian sediments, and these materials are likely currently saltating. Variations in the Thermal Inertia within interior layered deposits in Hebes Chasma can be distinguished, and the Thermal Inertia is too low to be consistent with bedrock or a lava flow. Thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation. Higher-resolution THEMIS Thermal Inertia enables the identification of exposed bedrock on the Martian surface. In Nili Patera and Ares Vallis, bedrock material corresponds to distinct compositional and morphologic surfaces, indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes.
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high resolution Thermal Inertia derived from the Thermal emission imaging system themis Thermal model and applications
Journal of Geophysical Research, 2006Co-Authors: Robin L. Fergason, Philip R Christensen, Hugh H KiefferAbstract:[1] Thermal Inertia values at 100 m per pixel are determined using nighttime temperature data from the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft, producing the highest-resolution Thermal Inertia data set to date. THEMIS Thermal Inertia values have an overall accuracy of ∼20%, a precision of 10–15%, and are consistent with both Thermal Emission Spectrometer orbital and Miniature Thermal Emission Spectrometer surface Thermal Inertia values. This data set enables the improved quantification of fine-scale surface details observed in high-resolution visible images. In the Tharsis region, surface textures and crater rims observed in visible images have no corresponding variation in the THEMIS Thermal Inertia images, indicating that the dust mantle is pervasive at THEMIS scales and is a minimum of a few centimeters and up to 1–2 m thick. The Thermal Inertia of bed form material indicates particle diameters expected for aeolian sediments, and these materials are likely currently saltating. Variations in the Thermal Inertia within interior layered deposits in Hebes Chasma can be distinguished, and the Thermal Inertia is too low to be consistent with bedrock or a lava flow. Thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation. Higher-resolution THEMIS Thermal Inertia enables the identification of exposed bedrock on the Martian surface. In Nili Patera and Ares Vallis, bedrock material corresponds to distinct compositional and morphologic surfaces, indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes.
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High-Resolution Thermal Inertia Mapping from the Mars Global Surveyor Thermal Emission Spectrometer
Icarus, 2000Co-Authors: Michael T Mellon, Hugh H Kieffer, Bruce M. Jakosky, Philip R ChristensenAbstract:Abstract High-resolution Thermal Inertia mapping results are presented, derived from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) observations of the surface temperature of Mars obtained during the early portion of the MGS mapping mission. Thermal Inertia is the key property controlling the diurnal surface temperature variations, and is dependent on the physical character of the top few centimeters of the surface. It represents a complex combination of particle size, rock abundance, exposures of bedrock, and degree of induration. In this work we describe the derivation of Thermal Inertia from TES data, present global scale analysis, and place these results into context with earlier work. A global map of nighttime Thermal-bolometer-based Thermal Inertia is presented at 1 4 ° per pixel resolution, with approximately 63% coverage between 50°S and 70°N latitude. Global analysis shows a similar pattern of high and low Thermal Inertia as seen in previous Viking low-resolution mapping. Significantly more detail is present in the high-resolution TES Thermal Inertia. This detail represents horizontal small-scale variability in the nature of the surface. Correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate-to-high Thermal Inertia and intermediate albedo. This new unit has a modal peak Thermal Inertia of 180–250 J m−2 K−1 s− 1 2 and a narrow range of albedo near 0.24. The unit, covering a significant fraction of the surface, typically surrounds the low Thermal Inertia regions and may comprise a deposit of indurated fine material. Local 3-km-resolution maps are also presented as examples of eolian, fluvial, and volcanic geology. Some impact crater rims and intracrater dunes show higher Thermal Inertias than the surrounding terrain; Thermal Inertia of aeolian deposits such as intracrater dunes may be related to average particle size. Outflow channels and valleys consistently show higher Thermal Inertias than the surrounding terrain. Generally, correlations between spatial variations in Thermal Inertia and geologic features suggest a relationship between the hundred-meter-scale morphology and the centimeter-scale surface layer.
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The Thermal Inertia of Mars from the Mars Global Surveyor Thermal Emission Spectrometer
Journal of Geophysical Research, 2000Co-Authors: Bruce M. Jakosky, Hugh H Kieffer, Michael T Mellon, P. R. Christensen, E. Stacy VarnesAbstract:We have used Mars Global Surveyor (MGS) Thermal Emission Spectrometer Thermal emission measurements to derive the Thermal Inertia of the Martian surface at the ∼100-km spatial scale. We have validated the use of nighttime-only measurements to derive Thermal Inertia as well as the use of a single wavelength band versus bolometric Thermal emission measurements. We have also reanalyzed the Viking Infrared Thermal Mapper data set in a similar manner in order to allow a direct comparison between the two. Within the uncertainties of the fit of the data to the model, and the uncertainties inherent in the model, the Thermal Inertia has not changed substantially in the 21 years between the Viking and the MGS measurements. Although some differences are seen, they are most likely due to changes in albedo during the intervening years or to residual effects of airborne dust that are not fully accounted for in the Thermal models. The Thermal Inertia values that we derive, between about 24 and 800 J m−2 s−1/2 K−1, are thought to better represent the actual Thermal Inertia of the Martian surface than previous estimates.
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high resolution Thermal Inertia mapping from the mars global surveyor Thermal emission spectrometer
Lunar and Planetary Science Conference, 2000Co-Authors: Michael T Mellon, Hugh H Kieffer, Bruce M. Jakosky, Philip R ChristensenAbstract:High-resolution Thermal Inertia mapping results are presented, derived from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) observations of the surface temperature of Mars obtained during the early portion of the MGS mapping mission. Thermal Inertia is the key property controlling the diurnal surface temperature variations, and is dependent on the physical character of the top few centimeters of the surface. It represents a complex combination of particle size, rock abundance, exposures of bedrock, and degree of induration. In this work we describe the derivation of Thermal Inertia from TES data, present global scale analysis, and place these results into context with earlier work. A global map of nighttime Thermal-bolometer-based Thermal Inertia is presented at 1 ‐ per pixel resolution, with approximately 63% coverage between 50 ‐ S and 70 ‐ N latitude. Global analysis shows a similar pattern of high and low Thermal Inertia as seen in previous Viking low-resolution mapping. Significantly more detail is present in the high-resolution TES Thermal Inertia. This detail represents horizontal small-scale variability in the nature of the surface. Correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate-to-high Thermal Inertia and intermediate albedo. This new unit has a modal peak Thermal Inertia of 180‐ 250 Jm i 2 K i 1 s i 1 2 and a narrow range of albedo near 0.24. The unit, covering a significant fraction of the surface, typically surrounds the low Thermal Inertia regions and may comprise a deposit of indurated fine material. Local 3-km-resolution maps are also presented as examples of eolian, fluvial, and volcanic geology. Some impact crater rims and intracrater dunes show higher Thermal Inertias than the surrounding terrain; Thermal Inertia of aeolian deposits such as intracrater dunes may be related to average particle size. Outflow channels and valleys consistently show higher Thermal Inertias than the surrounding terrain. Generally, correlations between spatial variations in Thermal Inertia and geologic features suggest a relationship between the hundred-meter-scale morphology and the centimeter-scale surface layer. c ∞ 2000 Academic Press
Alan W. Harris - One of the best experts on this subject based on the ideXlab platform.
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The relevance of Thermal Inertia to planetary defense
2017Co-Authors: Alan W. Harris, Line DrubeAbstract:One of the largest uncertainties in the outcome of an attempt to deflect an asteroid with a kinetic impactor is the momentum enhancement factor, β, which is related to the amount of momentum carried off by ejecta produced by the impact. The momentum enhancement of an asteroid due to ejecta is proportional to (β-1). The amount and velocity distribution of ejecta depends on the porosity and density of the surface material, characteristics that are closely related to Thermal Inertia. We show how it is possible to estimate the surface Thermal Inertia of an asteroid from Earth-based infrared observations, such as those carried out by NASA’s Wide-field Infrared Survey Explorer (WISE) space telescope, and thereby provide information on physical characteristics relevant to asteroid deflection. Recent research results suggest the Thermal Inertia of near-Earth objects (NEOs), and therefore the density and Thermal conductivity of near-surface material, increases rapidly with depth within the topmost 1m. If density increases with depth, the value of β relevant to the kinetic impactor concept will be larger in general than that implied by the properties of material on the surface. Furthermore, Thermal conductivity is an important parameter in calculations of the Yarkovsky orbital drift of NEOs. We briefly describe the relevant observational results and discuss their implications for the effectiveness of the kinetic impactor deflection concept, and for calculations of the Yarkovsky effect relevant to the impact hazard.
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Discovery of spin-rate-dependent asteroid Thermal Inertia
2016Co-Authors: Alan W. Harris, Line DrubeAbstract:Knowledge of the surface Thermal Inertia of an asteroid can provide insight into surface structure: porous material has a lower Thermal Inertia than rock. Using WISE/NEOWISE data and our new asteroid Thermal-Inertia estimator we show that the Thermal Inertia of main-belt asteroids (MBAs) appears to increase with spin period. Similar behavior is found in the case of thermophysically-modeled Thermal Inertia values of near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and Thermal conductivity with depth, and provide evidence that Thermal Inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. On the basis of a picture of depth-dependent Thermal Inertia our results suggest that, in general, Thermal Inertia values representative of solid rock are reached some tens of centimeters to meters below the surface in the case of MBAs (the median diameter in our dataset = 24 km). In the case of the much smaller (km-sized) NEOs a thinner porous surface layer is indicated, with large pieces of solid rock possibly existing just a meter or less below the surface. These conclusions are consistent with our understanding from in-situ measurements of the surfaces of the Moon, and a few asteroids, and suggest a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids. Our results have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of Thermal Inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles ("kinetic impactors") in planetary defense.
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A novel and simple means to estimate asteroid Thermal Inertia
2016Co-Authors: Line Drube, Alan W. HarrisAbstract:Calculating accurate values of Thermal Inertia for asteroids is a difficult process requiring a shape model, Thermal-infrared observations of the object obtained over broad ranges of rotation period and aspect angle, and detailed thermophysical modeling. Consequently, reliable Thermal Inertia values are currently available for relatively few asteroids. On the basis of simple asteroid Thermal modeling we have developed an empirical relationship enabling the Thermal Inertia of an asteroid to be estimated given adequate measurements of its Thermal-infrared continuum and knowledge of its spin vector. In particular, our Thermal-Inertia estimator can be applied to hundreds of objects in the WISE cryogenic archive (limited by the availability of spin vectors). To test the accuracy of our Thermal-Inertia estimator we have used it to estimate Thermal Inertia for near-Earth asteroids, main-belt asteroids, Centaurs, and trans-Neptunian objects with known Thermal Inertia values derived from detailed thermophysical modeling. In nearly all cases the estimates agree within the error bars with the values derived from thermophysical modeling.
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Eclipsing Binary Trojan Asteroid Patroclus: Thermal Inertia from Spitzer Observations
Icarus, 2010Co-Authors: Michael Mueller, Daniel Hestroffer, Jérôme Berthier, Stefano Mottola, Alan W. Harris, Joshua P. Emery, Franck Marchis, Mario Di MartinoAbstract:We present mid-infrared (8-33 micron) observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope.F or the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the Thermal Inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system's known mutual orbit, arbitrary component shapes, and Thermal conduction in the presence of eclipses. We obtain two local Thermal-Inertia values, representative of the respective shadowed areas: 21+/14 MKS and 6.4+/-1.6 MKS. The average Thermal Inertia is estimated to be 20+/-15 MKS, potentially with significant surface heterogeneity. This first Thermal-Inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and 98+/-10 km, respectively, in agreement with previous findings. Taken together with the system's known total mass, this implies a bulk mass density of 1.08 +/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice.
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Eclipsing binary Trojan asteroid Patroclus: Thermal Inertia from Spitzer observations
Icarus, 2010Co-Authors: Michael Mueller, Daniel Hestroffer, Jérôme Berthier, Stefano Mottola, Alan W. Harris, Joshua P. Emery, Franck Marchis, Mario Di MartinoAbstract:48 pages, 6 tables, 5 figures. The original publication is available in Icarus (www.elsevier.com/locate/icarus).International audienceWe present mid-infrared (8-33 micron) observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope.F or the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the Thermal Inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system's known mutual orbit, arbitrary component shapes, and Thermal conduction in the presence of eclipses. We obtain two local Thermal-Inertia values, representative of the respective shadowed areas: 21+/14 MKS and 6.4+/-1.6 MKS. The average Thermal Inertia is estimated to be 20+/-15 MKS, potentially with significant surface heterogeneity. This first Thermal-Inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and 98+/-10 km, respectively, in agreement with previous findings. Taken together with the system's known total mass, this implies a bulk mass density of 1.08 +/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice
