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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
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NASA NTRS1993

Numerical simulation of lava flows: Applications to the terrestrial planets

Lava flows are the visible expression of the extrusion of volcanic materials on a variety of planetary surfaces. A computer program described by Ishihara et al. appears to be well suited for application to different environments, and we have undertaken tests to evaluate their approach. Our results are somewhat mixed; the program does reproduce reasonable lava flow behavior in many situations, but we have encountered some conditions common to planetary environments for which the current program is inadequate. Here we present our initial efforts to identify the 'parameter space' for reasonable numerical simulations of lava flows.

Zimbelman, James R.↗
NASA NTRS1993

Aspects of modelling the tectonics of large volcanoes on the terrestrial planets

Analytic solutions for the response of planetary lithospheres to volcanic loads have been used to model faulting and infer elastic plate thicknesses. Predictions of the distribution of faulting around volcanic loads, based on the application of Anderson's criteria for faulting to the results of the models, do not agree well with observations. Such models do not give the stress state and stress history within the edifice. The effects of episodic load growth can also be treated. When these effects are included, models give much better agreement with observations.

Mcgovern, Patrick J.↗
NASA NTRS1994

Degassing history and evolution of volcanic activity of terrestrial planets based on radiogenic noble gas degassing models

Current abundances of radiogenic noble gases (4-He, 40-Ar, 129-Xe) in the planetary atmospheres provide valuable information on planetary evolution through their degassing histories. Of these, 40-Ar (from 40-K with half life 1.25 Ga) can be used to envisage long-term degassing from their interior. Present amounts of 36 and 40-Ar should have information on timing and degree of degassing from the interior. On the other hand, 129-Xe (from 129-I with half life 17 Ma) is used in discussing early planetary degassing. Because life time of helium in the atmosphere is short, atmospheric 4-He (from 235-U, 238-U, 232-Th) data might be used only for current degassing. The relative abundance of 40-Ar in the Cytherean atmosphere is 0.26 of that in the Earth's atmosphere. We have executed numerical calculation of a 40-Ar degassing model along with mantle evolution and melt migration. Our result shows that the average magma production rate on Venus is about 5 (km(exp 3)/yr). Duration of plate motion on Venus, if existed, would be less than several hundred million years.

Sasaki, S.↗
NASA NTRS1994

Water abundance and accretion history of terrestrial planets

According to a widespread believe, Earth's water was either added in form of a late volatile-rich veneer or as we have argued repeatedly that of all the water which was added to the Earth only that portion remained which was added towards the end of accretion when the mean oxygen fugacity of the accreting material became so high that metallic iron could not exist any longer. Prior to this moment, all the water in the latter scenario would have been used up for the oxidation of iron. Fe + H2O yields FeO + H2. Huge quantities of hydrogen would continuously be produced in this scenario which escaped. In the same moment the hydrogen on its way to the surface would lead to an efficient degassing of the growing Earth's mantle. The fact that - assuming C1 abundances - the amount of iridium in the Earth's mantle agrees, within a factor of two with the total water inventory of the Earth's mantle and crust is taken as evidence for the validity of such a scenario. In both scenarios, the Earth's mantle would remain dry and devoid of other volatiles. Some species soluble in metallic iron like carbon and hydrogen will probably partly enter the core in some portions. It is generally assumed that today a considerable portion of the earth's total water inventory resides in the mantle. It is also clear that over the history of the Earth the water of the Earth's oceans has been recycled many times through the mantle. This is the consequence of plate subduction. In a similar way mantle convection was probably responsible to being water into the originally dry mantle. As a consequence, today the Earth is wet both inside and outside.

Waenke, H.↗
NASA NTRS1994

Episodic large-scale overturn of two-layer mantles in terrestrial planets

It is usually assumed that the upper and lower mantles of a chemically stratified planet are arranged so that the upper mantle is chemically less dense and that these layers convect separately. Possible buoyant overturn of the two mantle layers has not previously been considered. Such overturn would initially occur when thermal expansion of a chemically denser lower mantle more than offsets the compositional density difference between the layers, reversing the relative sense of buoyancy. Once overturn has occurred, the chemically denser, but thermally less dense upper mantle cools more efficiently than the lower mantle and loses its relative thermal buoyancy. If mixing is slow, this leads to repeated overturns that result in thermal histories that differ radically from those obtained without this large-scale overturning. Thermal evolution calculations, for a two-layer mantle over a wide range of parameter space, show that large-scale overturn occurs cyclically with a well-defined period. This period depends most strongly on the viscosity of the lower mantle, to which it is approximately proportional. Geologically interesting overturn periods on the order of 10(exp 7) to 10(exp 9) years result for lower mantle viscosities of 10(exp 22) to 10(exp 24) Pa s for the Earth and Venus, and 10(exp 21) to 10(exp 23) Pa s for Mars. The mantles of Mercury and the Moon are too thin to permit two-layer convection, and therefore the model is not appropriate for them. Overturn cannot occur on Earth or Venus if the compositional density difference between the layers exceeds about 4%, or on Mars if it exceeds about 2%. Large-scale mantle overturn could have significant tectonic consequences such as the initiation of a new plate tectonic cycle on the Earth or a major resurfacing event on Mars or Venus. Such episodic events in the evolution of a planet are not easily explained by whole mantle thermal convection.

Herrick, David L.↗
NASA NTRS1994

First measurement of helium on Mars: Implications for the problem of radiogenic gases on the terrestrial planets

108 +/- 11 photons of the martian He 584-A airglow detected by the Extreme Ultraviolet Explorer (EUVE) satellite during a 2-day exposure (January 22-23, 1993) correspond to the effective disk average intensity of 43 +/- 10 Rayleigh (Ra). Radiative transfer calculations, using a model atmosphere appropriate to the conditions of the observation and having an exospheric temperature of 210 +/- 20 K, result in a He mixing ratio of 1.1 +/- 0.4 ppm in the lower atmosphere. Nonthermal escape of helium is due to electron impact ionization and pickup of He(+) by the solar wind, to collisions with hot oxygen atoms, and to charge exchange with molecular species with corresponding column loss rates of 1.4 x 10(exp 5), 3 x 10(exp 4), and 7 x 10(exp 3)/sq cm/s, respectively. The lifetime of helium on Mars is 5 x 10(exp 4) years. the He outgassing rate, coupled with the Ar-40 atmospheric abundance and with the K:U:Th ratio measured in the surface rocks, is used as input to a single two-reservoir degassing model which is applied to Mars and then to Venus. A similar model with known abundances if K, U, and Th is applied to Earth. The models for Earth and Mars presume loss of all argon accumulated in the atmospheres during the first billion years by large-scale meteorite and planetesimal impacts. The models show that the degassing coefficients for all three planets may be approximated by function delta = delta(sub 0) x (t(sub 0)/t)(exp 1/2) with delta(sub 0) = 0.1, 0.04, and 0.0125 Byr for Earth, Venus, and Mars, respectively. After a R(exp 2) correction this means that outgassing processes on Venus and Mars are weaker than on Earth by factors of 3 and 30, respectively. Mass ratios of U and Th are almost the same for all three planets, while potassiumis depleted by a factor of 2 in Venus and Mars. Mass ratio of helium and argon are close to 5 x 10(exp -9) and 2 x 10(exp -8) g/g in the interiors of all three planets. The implications of these results are discussed.

Krasnopolsky, V. A.↗
NASA NTRS1994

CO2 cooling in terrestrial planet thermospheres

We examine the recent progress in the debate on the CO2-O relaxation rate, its temperature dependence, and its corresponding impact on the thermospheric heat budgets of Venus, Earth, and Mars. This comparative approach provides the broadest range of conditions under which a common CO2-O relaxation rate should provide consistent results. New global mean calculations are presented for the heat budgets of these three planets using large CO2-O relaxation rates that have been inferred recently from Earth CO2 radiance measurements and laboratory studies. Results indicate that available Venus and Mars data constrain the CO2-O relaxation rate to be 2-4 x 10(exp -12)/cu cm/s at 300 K. For Venus, this strong cooling serves as an effective thermostat that gives rise to a small variation of thermospheric temperatures over the solar cycle, just as observed. Conversely, CO2 cooling does not appear to be dominant in the dayside heat budget of the Mars thermosphere over most of the solar cycle. For the Earth, this strong cooling implies that the lower thermosphere does not typically require significant eddy diffusion or heat conduction. However, global-scale dynamics or an additional heating mechanism may be needed to restore calculated temperatures to observed values when relaxation rates exceeding 2 x 10(exp -12)/cu cm/s are employed.

Bougher, S. W.↗
NASA NTRS2000

A Balanced Model for Exploration of the Terrestrial Planets: Lessons from the Lunar Experience

The Moon is the only extraterrestrial rocky body for which we have a combination of surface-selected samples, high-resolution orbital photography (Lunar Orbiter), manned and robotic surface exploration (Surveyor, Apollo, Luna), and global compositional, mineralogical, and geophysical data (Galileo, Clementine, Lunar Prospector). Beginning in 1998, CAPTEM organized a series of workshops and conference sessions aimed at integrating these diverse data sets. The insights gained by bringing together scientists from the remote-sensing and sample-analysis communities have been singularly rewarding. Not least of these has been the recognition by both groups that having both kinds of data maximizes the scientific return and permits reconciling information from diverse scales and perspectives. The 20-20 hindsight of the Lunar experience thus provides important lessons; learning from mistakes as well as successes, we can derive a sensible scientific program for Mars exploration. In this abstract, we describe examples of key information from (a) in-situ geologic investigation, (b) laboratory analysis of returned samples whose geologic context and location are known, and (c) global remote sensing of mineralogy, composition, and geophysical parameters. We then show the value of integrating these diverse data sets.

Jolliff, B. L.↗
NASA NTRS2004

Water in Terrestrial Planets: Always an Oxidant?

Water is commonly assumed to be an oxidant in many planetary settings. Because it can affect Fe-FeO-Fe2O3 equilibria and thus bulk compositional properties of planets and asteroids, this is an important ingredient to understand. The role of water in two settings will be addressed - magmas, and mantles during accretion - along with the implications for planet growth and evolution.

Righter, K.↗
NASA NTRS2004

Migration of Dust Particles and Their Collisions with the Terrestrial Planets

Our review of previously published papers on dust migration can be found in [1], where we also present different distributions of migrating dust particles. We considered a different set of initial orbits for the dust particles than those in the previous papers. Below we pay the main attention to the collisional probabilities of migrating dust particles with the planets based on a set of orbital elements during their evolution. Such probabilities were not calculated earlier.

Ipatov, S. I.↗
NASA NTRS2004

Obliquity Variations of Extrasolar Terrestrial Planets

A planet's obliquity, which is the angle between its orbital angular momentum and its rotational angular momentum, is an important factor in determining its climate and habitability. For small obliquities, as well as obliquities close to 180 degrees, the planet receives more radiant energy from its star at equatorial latitudes than near its poles, whereas the poles are heated the most for obliquities near 90 degrees. Jacques Laskar has analyzed possible obliquity variations of the planets in our Solar System. His study also considers the same planets with different rotational periods, and the Earth without the Moon. He finds, using frequency map analysis, that the obliquity of the Earth is stabilized by the Moon, and can vary by at most a few degrees. In contrast, the obliquity of Mars can range from 0 to 60 degrees, and a hypothetical moonless Earth's axial tilt could be close to 0 degrees or as large as 85 degrees. Numerical integrations by Laskar and others have shown that Mars' obliquity indeed varies over most of its permitted range on time scales of tens of millions of years. In contrast, our analysis shows that the obliquity of a moonless Earth appears to be confined to the range of approximately 12 - 38 degrees over time scales of 100 million years. Results of ongoing longer integrations will be presented, and their implications discussed.

Lissauer, Jack J.↗
NASA NTRS2005

Terrestrial Planet Evolution

The goals of this proposal involved constructing 1:5M scale geologic maps of V-23 (Niobe Planitia) and V-24 (Greenaway) quadrangles, and ancillary materials to be submitted to USGS as part of the VMAP project. Complete geologic maps and packages of ancillary materials for V-23 and V-24 have been submitted to USGS and are currently under review. In addition to these products, we have published or submitted various manuscript and/abstracts detailing the results of our research that has grown out of the proposed work. We presented our maps in various stages of construction at NASA Planetary Geology and Geophysics Mappers' meeting each year. We have also presented talks or posters summarizing our work at various conferences including: he Lunar and Planetary Science Conference, and the National Geological Society of America meeting. The work resulted in exciting developments of Venus lowland resurfacing. The products and publications resulting from this work are listed below.

Hansen, Vicki L.↗