The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the ... more The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and H. Hanada et al.
Proceedings of the NIPR Symposium on Antarctic …, Jan 1, 1989
Implantation of the ancent solar wind is a possible noble gas source for Venus and gas-rich meteo... more Implantation of the ancent solar wind is a possible noble gas source for Venus and gas-rich meteorites. During the stage of planetary accretion, dust grains re-emitted by planetesimal collisions could be targets of the solar wind implantation. The present study shows that such off-disk ...
The three-dimensional numerical simulation code for nonisothermal Bingham fluid was applied to fo... more The three-dimensional numerical simulation code for nonisothermal Bingham fluid was applied to four typical crater outflows on Venus to estimate emplacement styles of outflow materials. We have succeeded in reproducing emplacement features qualitatively over digital elevation models (DEMs) obtained by the Magellan spacecraft, and we have shown that outflow materials can be formed by melts of basaltic crust. Therefore, the presence of crater outflows may not be evidence of the presence of previously suggested fluid materials, such as komatiite or carbonatite, although we failed to model the very low viscosity flow. Numerically estimated supply rates of flow materials are categorized into two types, a catastrophic style and a gentle style. Markham and Isabella crater outflows are examples of catastrophic styles, and the flow materials required to form them were probably supplied at higher rates than 10 10 m 3 /s and the durations of material supply were less than 100 s. This very high supply rate is difficult to attribute to any volcanic process because typical eruption rates of terrestrial volcanic flows are less than 8 or 9 orders of magnitude lower than that. Such a style of emplacement is more plausibly considered as a result of the impact itself, for example, a catastrophic debris flow or a vapor cloud triggered by the impact. On the other hand, supply rates of Willard and Xantippe outflows, which are considered gentle-style flows, were estimated to be about 10 4 m 3 /s and the durations were more than 10 5 s. Such a gentle style of outflow emplacement is probably not a direct result of the impact but is rather due to a secondary process, possibly segregation and drainage of impact melt materials from within previously emplaced ejecta materials, or post-impact volcanism.
The radiogenic noble gas species He, Ar, and Xe in the atmosphere of the terrestrial planets prov... more The radiogenic noble gas species He, Ar, and Xe in the atmosphere of the terrestrial planets provide valuable information on planetary degassing history. The abundance of radiogenic fraction of Martian atmospheric Xe relative to the total planetary mass suggests that early ...
We present the specifications of the Mars Imaging Camera (MIC) on the Planet-B spin-stabilized sp... more We present the specifications of the Mars Imaging Camera (MIC) on the Planet-B spin-stabilized spacecraft, and key scientific objectives of MIC observations. A non-sun-synchronous orbit of Planet-B with a large eccentricity of about 0.87 around Mars provides the opportunities (1) to observe the same region of Mars at various times of day and various solar phase angles with spatial resolution of about 60 m from a distance of 150 km altitude (at periapsis), and (2) to monitor changes of global atmospheric conditions on Mars near an apoapsis of 15 Mars radii. In addition, (3) several encounters of Planet-B with each of the two Martian satellites are scheduled during the mission lifetime of two years from October 1999 to observe their shapes and surface structures with three color filters, centered on 450, 550, and 650 nm. (4) A search for hypothetical dust rings along the orbits of two satellites will be tried from the forward-scattering region of sunlight.
We estimate the orientations of crustal stress on Venus from surface geometry of dike swarms asso... more We estimate the orientations of crustal stress on Venus from surface geometry of dike swarms associated with volcanoes. The inferred stress field sometimes has various orientations even in the same region. Using lava stratigraphy, volcanoes in the Beta‐Atla‐Themis (BAT) ...
Abstract We have newly developed a scheme for estimating the degree of space weathering which is ... more Abstract We have newly developed a scheme for estimating the degree of space weathering which is more free from effects of grain size and viewing geometry, utilizing the spectral inflections at around 0.4 and 0.55 µm. It is very useful for planetary remote sensing ...
Two small satellites of Mars, Phobos and Deimos, can be dust sources around Mars. Orbits of circu... more Two small satellites of Mars, Phobos and Deimos, can be dust sources around Mars. Orbits of circummartian dust particles are controlled by solar radiation pressure as well as Martian oblateness. Their orbital eccentricity and inclination can be enhanced greatly by the orbital resonance. Particles from Phobos would form a thin dust ring where dust radius is dominant in '20-20&m. On the other hand, particles from Deimos would form an extended dust torus. Collisions of ring particles on Phobos and Deimos may be the most important dust source. The upper limit of dust production from this self-sustaining mechanism can be estimated from the erosion rate of Phobos. Japanese Mars mission NOZOMI (PLANET-B) could discover dust rin~toms through direct detection by MIX (Mars Dust Counter). 0 1999 COSPAR. Published by Elsevier Science Ltd.
1] The geomorphology of the North East trending long fractured depression between the Ganges Chas... more 1] The geomorphology of the North East trending long fractured depression between the Ganges Chasma and the Shalbatana Vallis headwater source region is examined and interpreted to be the result of collapse of part of an extensive underground cavernous system. We propose that this cavernous system undermines at least a valley, which extends from the vicinities of the Ganges Chasma and terminates in the Shalbatana Vallis headwater source region and the Aromatum Chaos. We believe that the origin of this cavernous system was related to the formation and interconnection of discrete cavernous bodies and propose a hypothesis, which involves the interaction of permafrost and intrusive magmatism to explain their formation. The Shalbatana Vallis headwater source is interpreted as produced by a Noachian impact crater and surface collapse over part of the underground cavernous system. Finally, we propose that the water sources, which were involved in the excavation of the Shalbatana and Ravis outflow channels might have included water segregated from the permafrost through interaction of intrusive magmatism and permafrost, water drained from a paleolake in the Ganges Chasma and water released from the catastrophic evacuation of confined aquifers.
We determined the morphologies and dimensions of possible impact craters on the surface of Astero... more We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough, smooth and saddle-shaped floors, a lack of raised rims and fresh material exposures. The average depth/diameter ratio was 0.08 ± 0.03: these craters are very shallow relative to craters observed on other asteroids.
S-type asteroids are believed to be parent bodies of ordinary chondrites. However, the reflectanc... more S-type asteroids are believed to be parent bodies of ordinary chondrites. However, the reflectance spectra of S-type asteroids are different from those of ordinary chondrites. This spectral mismatch is strongly considered as a result of space weathering, where high-velocity dust particle impacts should change the optical properties of the uppermost regolith surface of asteroids. To simulate space weathering by impact heating of dust particles, we irradiated nanosecond pulse laser beam onto planetary surface materials, whose pulse duration and energy rate are comparable with those of real dust impacts. The laser-irradiated samples show optical changes similar to that by space weathering, and contain nanophase metallic iron particles considered as the essential cause of space weathering. After laser-irradiations, we observed the samples by an Electron Spin Resonance (ESR) to perform quantitative analysis of nanophase metallic iron particles. We report the first description that the quantities of nanophase metallic iron particles in olivine samples increase at higher space weathering degree.
Background: Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo re... more Background: Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo regions covered with widespread sedimentary deposits that are thick enough to partly or completely suppress the signature of the residual water ice that forms the uppermost zone of the polar layered deposits. These sedimentary deposits appear to have a source primarily in a buried sedimentary layer preferentially exposed along the walls and floors of some polar troughs. The deposits extend and drape over circum-polar dunes.
Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type a... more Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type and MORB-type. The estimated high 3 He and 22 Ne abundances of the PLUME source, possibly representing the lower mantle, should re¯ect the remnant of dissolved solar-type atmosphere. Calculations of the structure of the primary atmosphere and the noble gas dissolution into the magma ocean of the accreting planet suggest that the high 3 He and 22 Ne abundances can be explained if the primary atmosphere persisted until M H0.4±0.6 M E (M E being the present Earth mass). The PLUME source has higher 3 He/ 4 He and lower 21 Ne/ 22 Ne than the MORB source. This is explained by assuming that the lower mantle was less degassed during magma ocean cooling. The carbon abundance in the mantle can be constrained from the estimated abundance of mantle 3 He and C/ 3 He data of the present mantle-derived samples. Dissolved solar-type noble gas might explain high noble gas abundance in the present Venus, if the primary atmosphere persisted until the ®nal stage of accretion under lower dust opacity of the atmosphere. #
We have conducted J, H, and K S imaging observations for the Coalsack Globule 2 with the SIRIUS i... more We have conducted J, H, and K S imaging observations for the Coalsack Globule 2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope at SAAO, and determined the color excess ratio, E J−H /E H−K S . The ratio is determined in the same photometric system as our previous study for the ρ Oph and Cha clouds without any color transformation; this enables us to directly compare the nearinfrared extinction laws among these regions. The current ratio E J−H /E H−K S = 1.91 ± 0.01 for the extinction range 0.5 < E J−H < 1.8 is significantly larger than the ratios for the ρ Oph and Cha clouds (E J−H /E H−K S = 1.60-1.69). This ratio corresponds to a large negative index α = 2.34 ± 0.01 when the wavelength dependence of extinction is approximated by a power law A λ ∝ λ −α , which might indicate little growth of dust grains, or larger abundance of dielectric nonabsorbing components such as silicates, or both in this cloud. We also confirm that the color excess ratio for the Coalsack Globule 2 has a trend of increasing with decreasing optical depth, which is the same trend as the ρ Oph and Cha clouds have.
Which mechanism determines the planetary atmospheric inventories of various gases is an important... more Which mechanism determines the planetary atmospheric inventories of various gases is an important problem. It has been suggested that Venus&#x27; atmospheric CO 2 abundance is controlled or buffered by carbonation reaction on the surface (carbonate buffer). According to this hypothesis, ...
Accurate estimates of the duration and volume of extrusive volcanism of the Moon are essential fo... more Accurate estimates of the duration and volume of extrusive volcanism of the Moon are essential for understanding the lunar thermal evolution. Here, using new high-resolution images obtained by the SELENE Terrain Camera, we determined the thicknesses and ...
Space weathering is a process where formation of nanophase iron particles causes darkening of ove... more Space weathering is a process where formation of nanophase iron particles causes darkening of overall reflectance, spectral reddening, and weakening of absorption bands on atmosphereless bodies such as the moon and asteroids. Using pulse laser irradiation, formation of nanophase iron particles by micrometeorite impact heating is simulated. Although Mercurian surface is poor in iron and rich in anorthite, microscopic process of nanophase iron particle formation can take place on Mercury. On the other hand, growth of nanophase iron particles through Ostwald ripening or repetitive dust impacts would moderate the weathering degree. Future MESSENGER and BepiColombo mission will unveil space weathering on Mercury through multispectral imaging observations.
A simple numerical simulation code is developed to quantitatively discuss the behaviors of past c... more A simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods, whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data. The code aims to keep the basic equations simple and the required computational costs low, which allows greater exploration of parameter space. Examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth-averaged diffusion wave approximation in two dimensions, as well as Manning's empirical equation for simplification. On the other hand, topography is included as a boundary condition, since topography plays an important role in selecting flood routes. The model provides important advantages over theoretical analyses or one-dimensional simulations, including: (1) the reproduction of complicated water flow paths such as bifurcations and reconvergences; (2) the reconstruction of hydrological relationships among the water paths; and (3) the direct comparison among the calculated extent of the flood inundation (including floodwater depths) and geological and geomorphological observations. Preliminary reconstructions of the Missoula floods demonstrate the advantages of this new approach. The method of coupling field-based flood information with two-dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on Earth with direct bearing on the understanding of regional paleohydrological histories of Mars. D
The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the ... more The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and H. Hanada et al.
Proceedings of the NIPR Symposium on Antarctic …, Jan 1, 1989
Implantation of the ancent solar wind is a possible noble gas source for Venus and gas-rich meteo... more Implantation of the ancent solar wind is a possible noble gas source for Venus and gas-rich meteorites. During the stage of planetary accretion, dust grains re-emitted by planetesimal collisions could be targets of the solar wind implantation. The present study shows that such off-disk ...
The three-dimensional numerical simulation code for nonisothermal Bingham fluid was applied to fo... more The three-dimensional numerical simulation code for nonisothermal Bingham fluid was applied to four typical crater outflows on Venus to estimate emplacement styles of outflow materials. We have succeeded in reproducing emplacement features qualitatively over digital elevation models (DEMs) obtained by the Magellan spacecraft, and we have shown that outflow materials can be formed by melts of basaltic crust. Therefore, the presence of crater outflows may not be evidence of the presence of previously suggested fluid materials, such as komatiite or carbonatite, although we failed to model the very low viscosity flow. Numerically estimated supply rates of flow materials are categorized into two types, a catastrophic style and a gentle style. Markham and Isabella crater outflows are examples of catastrophic styles, and the flow materials required to form them were probably supplied at higher rates than 10 10 m 3 /s and the durations of material supply were less than 100 s. This very high supply rate is difficult to attribute to any volcanic process because typical eruption rates of terrestrial volcanic flows are less than 8 or 9 orders of magnitude lower than that. Such a style of emplacement is more plausibly considered as a result of the impact itself, for example, a catastrophic debris flow or a vapor cloud triggered by the impact. On the other hand, supply rates of Willard and Xantippe outflows, which are considered gentle-style flows, were estimated to be about 10 4 m 3 /s and the durations were more than 10 5 s. Such a gentle style of outflow emplacement is probably not a direct result of the impact but is rather due to a secondary process, possibly segregation and drainage of impact melt materials from within previously emplaced ejecta materials, or post-impact volcanism.
The radiogenic noble gas species He, Ar, and Xe in the atmosphere of the terrestrial planets prov... more The radiogenic noble gas species He, Ar, and Xe in the atmosphere of the terrestrial planets provide valuable information on planetary degassing history. The abundance of radiogenic fraction of Martian atmospheric Xe relative to the total planetary mass suggests that early ...
We present the specifications of the Mars Imaging Camera (MIC) on the Planet-B spin-stabilized sp... more We present the specifications of the Mars Imaging Camera (MIC) on the Planet-B spin-stabilized spacecraft, and key scientific objectives of MIC observations. A non-sun-synchronous orbit of Planet-B with a large eccentricity of about 0.87 around Mars provides the opportunities (1) to observe the same region of Mars at various times of day and various solar phase angles with spatial resolution of about 60 m from a distance of 150 km altitude (at periapsis), and (2) to monitor changes of global atmospheric conditions on Mars near an apoapsis of 15 Mars radii. In addition, (3) several encounters of Planet-B with each of the two Martian satellites are scheduled during the mission lifetime of two years from October 1999 to observe their shapes and surface structures with three color filters, centered on 450, 550, and 650 nm. (4) A search for hypothetical dust rings along the orbits of two satellites will be tried from the forward-scattering region of sunlight.
We estimate the orientations of crustal stress on Venus from surface geometry of dike swarms asso... more We estimate the orientations of crustal stress on Venus from surface geometry of dike swarms associated with volcanoes. The inferred stress field sometimes has various orientations even in the same region. Using lava stratigraphy, volcanoes in the Beta‐Atla‐Themis (BAT) ...
Abstract We have newly developed a scheme for estimating the degree of space weathering which is ... more Abstract We have newly developed a scheme for estimating the degree of space weathering which is more free from effects of grain size and viewing geometry, utilizing the spectral inflections at around 0.4 and 0.55 µm. It is very useful for planetary remote sensing ...
Two small satellites of Mars, Phobos and Deimos, can be dust sources around Mars. Orbits of circu... more Two small satellites of Mars, Phobos and Deimos, can be dust sources around Mars. Orbits of circummartian dust particles are controlled by solar radiation pressure as well as Martian oblateness. Their orbital eccentricity and inclination can be enhanced greatly by the orbital resonance. Particles from Phobos would form a thin dust ring where dust radius is dominant in '20-20&m. On the other hand, particles from Deimos would form an extended dust torus. Collisions of ring particles on Phobos and Deimos may be the most important dust source. The upper limit of dust production from this self-sustaining mechanism can be estimated from the erosion rate of Phobos. Japanese Mars mission NOZOMI (PLANET-B) could discover dust rin~toms through direct detection by MIX (Mars Dust Counter). 0 1999 COSPAR. Published by Elsevier Science Ltd.
1] The geomorphology of the North East trending long fractured depression between the Ganges Chas... more 1] The geomorphology of the North East trending long fractured depression between the Ganges Chasma and the Shalbatana Vallis headwater source region is examined and interpreted to be the result of collapse of part of an extensive underground cavernous system. We propose that this cavernous system undermines at least a valley, which extends from the vicinities of the Ganges Chasma and terminates in the Shalbatana Vallis headwater source region and the Aromatum Chaos. We believe that the origin of this cavernous system was related to the formation and interconnection of discrete cavernous bodies and propose a hypothesis, which involves the interaction of permafrost and intrusive magmatism to explain their formation. The Shalbatana Vallis headwater source is interpreted as produced by a Noachian impact crater and surface collapse over part of the underground cavernous system. Finally, we propose that the water sources, which were involved in the excavation of the Shalbatana and Ravis outflow channels might have included water segregated from the permafrost through interaction of intrusive magmatism and permafrost, water drained from a paleolake in the Ganges Chasma and water released from the catastrophic evacuation of confined aquifers.
We determined the morphologies and dimensions of possible impact craters on the surface of Astero... more We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough, smooth and saddle-shaped floors, a lack of raised rims and fresh material exposures. The average depth/diameter ratio was 0.08 ± 0.03: these craters are very shallow relative to craters observed on other asteroids.
S-type asteroids are believed to be parent bodies of ordinary chondrites. However, the reflectanc... more S-type asteroids are believed to be parent bodies of ordinary chondrites. However, the reflectance spectra of S-type asteroids are different from those of ordinary chondrites. This spectral mismatch is strongly considered as a result of space weathering, where high-velocity dust particle impacts should change the optical properties of the uppermost regolith surface of asteroids. To simulate space weathering by impact heating of dust particles, we irradiated nanosecond pulse laser beam onto planetary surface materials, whose pulse duration and energy rate are comparable with those of real dust impacts. The laser-irradiated samples show optical changes similar to that by space weathering, and contain nanophase metallic iron particles considered as the essential cause of space weathering. After laser-irradiations, we observed the samples by an Electron Spin Resonance (ESR) to perform quantitative analysis of nanophase metallic iron particles. We report the first description that the quantities of nanophase metallic iron particles in olivine samples increase at higher space weathering degree.
Background: Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo re... more Background: Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo regions covered with widespread sedimentary deposits that are thick enough to partly or completely suppress the signature of the residual water ice that forms the uppermost zone of the polar layered deposits. These sedimentary deposits appear to have a source primarily in a buried sedimentary layer preferentially exposed along the walls and floors of some polar troughs. The deposits extend and drape over circum-polar dunes.
Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type a... more Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type and MORB-type. The estimated high 3 He and 22 Ne abundances of the PLUME source, possibly representing the lower mantle, should re¯ect the remnant of dissolved solar-type atmosphere. Calculations of the structure of the primary atmosphere and the noble gas dissolution into the magma ocean of the accreting planet suggest that the high 3 He and 22 Ne abundances can be explained if the primary atmosphere persisted until M H0.4±0.6 M E (M E being the present Earth mass). The PLUME source has higher 3 He/ 4 He and lower 21 Ne/ 22 Ne than the MORB source. This is explained by assuming that the lower mantle was less degassed during magma ocean cooling. The carbon abundance in the mantle can be constrained from the estimated abundance of mantle 3 He and C/ 3 He data of the present mantle-derived samples. Dissolved solar-type noble gas might explain high noble gas abundance in the present Venus, if the primary atmosphere persisted until the ®nal stage of accretion under lower dust opacity of the atmosphere. #
We have conducted J, H, and K S imaging observations for the Coalsack Globule 2 with the SIRIUS i... more We have conducted J, H, and K S imaging observations for the Coalsack Globule 2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope at SAAO, and determined the color excess ratio, E J−H /E H−K S . The ratio is determined in the same photometric system as our previous study for the ρ Oph and Cha clouds without any color transformation; this enables us to directly compare the nearinfrared extinction laws among these regions. The current ratio E J−H /E H−K S = 1.91 ± 0.01 for the extinction range 0.5 < E J−H < 1.8 is significantly larger than the ratios for the ρ Oph and Cha clouds (E J−H /E H−K S = 1.60-1.69). This ratio corresponds to a large negative index α = 2.34 ± 0.01 when the wavelength dependence of extinction is approximated by a power law A λ ∝ λ −α , which might indicate little growth of dust grains, or larger abundance of dielectric nonabsorbing components such as silicates, or both in this cloud. We also confirm that the color excess ratio for the Coalsack Globule 2 has a trend of increasing with decreasing optical depth, which is the same trend as the ρ Oph and Cha clouds have.
Which mechanism determines the planetary atmospheric inventories of various gases is an important... more Which mechanism determines the planetary atmospheric inventories of various gases is an important problem. It has been suggested that Venus&#x27; atmospheric CO 2 abundance is controlled or buffered by carbonation reaction on the surface (carbonate buffer). According to this hypothesis, ...
Accurate estimates of the duration and volume of extrusive volcanism of the Moon are essential fo... more Accurate estimates of the duration and volume of extrusive volcanism of the Moon are essential for understanding the lunar thermal evolution. Here, using new high-resolution images obtained by the SELENE Terrain Camera, we determined the thicknesses and ...
Space weathering is a process where formation of nanophase iron particles causes darkening of ove... more Space weathering is a process where formation of nanophase iron particles causes darkening of overall reflectance, spectral reddening, and weakening of absorption bands on atmosphereless bodies such as the moon and asteroids. Using pulse laser irradiation, formation of nanophase iron particles by micrometeorite impact heating is simulated. Although Mercurian surface is poor in iron and rich in anorthite, microscopic process of nanophase iron particle formation can take place on Mercury. On the other hand, growth of nanophase iron particles through Ostwald ripening or repetitive dust impacts would moderate the weathering degree. Future MESSENGER and BepiColombo mission will unveil space weathering on Mercury through multispectral imaging observations.
A simple numerical simulation code is developed to quantitatively discuss the behaviors of past c... more A simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods, whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data. The code aims to keep the basic equations simple and the required computational costs low, which allows greater exploration of parameter space. Examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth-averaged diffusion wave approximation in two dimensions, as well as Manning's empirical equation for simplification. On the other hand, topography is included as a boundary condition, since topography plays an important role in selecting flood routes. The model provides important advantages over theoretical analyses or one-dimensional simulations, including: (1) the reproduction of complicated water flow paths such as bifurcations and reconvergences; (2) the reconstruction of hydrological relationships among the water paths; and (3) the direct comparison among the calculated extent of the flood inundation (including floodwater depths) and geological and geomorphological observations. Preliminary reconstructions of the Missoula floods demonstrate the advantages of this new approach. The method of coupling field-based flood information with two-dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on Earth with direct bearing on the understanding of regional paleohydrological histories of Mars. D
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