2,412 research outputs found
Scatterometer Data Analysis program Final report, 1 Jun. 1968 - 31 May 1969
Evaluation and processing of scatterometer data for use in NASA Earth Resources Progra
Vesicularity, bubble formation and noble gas fractionation during MORB degassing
The objective of this study is to use molecular dynamics simulation (MD) to
evaluate the vesicularity and noble gas fractionation, and to shed light on
bubble formation during MORB degassing. A previous simulation study (Guillot
and Sator (2011) GCA 75, 1829-1857) has shown that the solubility of CO2 in
basaltic melts increases steadily with the pressure and deviates significantly
from Henry's law at high pressures (e.g. 9.5 wt% CO2 at 50 kbar as compared
with 2.5 wt% from Henry's law). From the CO2 solubility curve and the equations
of state of the two coexisting phases (silicate melt and supercritical CO2),
deduced from the MD simulation, we have evaluated the evolution of the
vesicularity of a MORB melt at depth as function of its initial CO2 contents.
An excellent agreement is obtained between calculations and data on MORB
samples collected at oceanic ridges. Moreover, by implementing the test
particle method (Guillot and Sator (2012) GCA 80, 51-69), the solubility of
noble gases in the two coexisting phases (supercritical CO2 and CO2-saturated
melt), the partitioning and the fractionation of noble gases between melt and
vesicles have been evaluated as function of the pressure. We show that the
melt/CO2 partition coefficients of noble gases increase significantly with the
pressure whereas the large distribution of the 4He/40Ar* ratio reported in the
literature is explained if the magma experiences a suite of vesiculation and
vesicle loss during ascent. By applying a pressure drop to a volatile bearing
melt, the MD simulation reveals the main steps of bubble formation and noble
gas transfer at the nanometric scale. A key result is that the transfer of
noble gases is found to be driven by CO2 bubble nucleation, a finding which
suggests that the diffusivity difference between He and Ar in the degassing
melt has virtually no effect on the 4He/40Ar* ratio measured in the vesicles.Comment: 42 pages, 8 figures. To be published in Chemical Geolog
A Time-Dependent Model of HD209458b
We developed a time-dependent radiative model for the atmosphere of HD209458b
to investigate its thermal structure and chemical composition. Time-dependent
temperature profiles were calculated, using a uniform zonal wind modelled as a
solid body rotation. We predict day/night temperature variations of 600K around
0.1 bar, for a 1 km/s wind velocity, in good agreement with the predictions by
Showman & Guillot (2002). On the night side, the low temperature allows the
sodium to condense. Depletion of sodium in the morning limb may explain the
lower than expected abundance found by Charbonneau et al (2002).Comment: 2 pages, LaTeX with 1 EPS figure embedded, using newpasp.sty
(supplied). To appear in the proceedings of the XIXth IAP colloquium
"Extrasolar Planets: Today and Tomorrow" held in Paris, France, 2003 June 30
-- July 4, ASP Conf. Se
Viscosity and viscosity anomalies of model silicates and magmas: a numerical investigation
We present results for transport properties (diffusion and viscosity) using
computer simulations. Focus is made on a densified binary sodium disilicate
2SiO-NaO (NS2) liquid and on multicomponent magmatic liquids (MORB,
basalt). In the NS2 liquid, results show that a certain number of anomalies
appear when the system is densified: the usual diffusivity maxima/minima is
found for the network-forming ions (Si,O) whereas the sodium atom displays
three distinct r\'egimes for diffusion. Some of these features can be
correlated with the obtained viscosity anomaly under pressure, the latter being
be fairly well reproduced from the simulated diffusion constant. In model
magmas (MORB liquid), we find a plateau followed by a continuous increase of
the viscosity with pressure. Finally, having computed both diffusion and
viscosity independently, we can discuss the validity of the Eyring equation for
viscosity which relates diffusion and viscosity. It is shown that it can be
considered as valid in melts with a high viscosity. On the overall, these
results highlight the difficulty of establishing a firm relationship between
dynamics, structure and thermodynamics in complex liquids.Comment: 13 pages, 8 figure
The Interiors of Giant Planets: Models and Outstanding Questions
We know that giant planets played a crucial role in the making of our Solar
System. The discovery of giant planets orbiting other stars is a formidable
opportunity to learn more about these objects, what is their composition, how
various processes influence their structure and evolution, and most importantly
how they form. Jupiter, Saturn, Uranus and Neptune can be studied in detail,
mostly from close spacecraft flybys. We can infer that they are all enriched in
heavy elements compared to the Sun, with the relative global enrichments
increasing with distance to the Sun. We can also infer that they possess dense
cores of varied masses. The intercomparison of presently caracterised
extrasolar giant planets show that they are also mainly made of hydrogen and
helium, but that they either have significantly different amounts of heavy
elements, or have had different orbital evolutions, or both. Hence, many
questions remain and are to be answered for significant progresses on the
origins of planets.Comment: 43 pages, 11 figures, 3 tables. To appear in Annual Review of Earth
and Planetary Sciences, vol 33, (2005
Recommended from our members
Assessing impacts to groundwater from CO2-flooding of SACROC and Claytonville oil fields in West Texas
Comparison of groundwater above two Permian Basin oil fields (SACROC Unit and
Claytonville Field) near Snyder, Texas should allow us to assess potential impacts of 30 years of
CO2-injection. CO2-flooding for enhanced oil recovery (EOR) has been active at SACROC in
Scurry County since 1972. Approximately 13.5 million tons per year (MtCO2/yr) are injected
with withdrawal/recycling amounting to ~7MtCO2/yr. It is estimated that the site has accumulated
more than 55MtCO2; however, no rigorous investigation of overlying groundwater has
demonstrated that CO2 is trapped in the subsurface. Mineralogy of reservoir rocks at the
Claytonville field in southwestern Fisher County is similar to SACROC. CO2-EOR is scheduled
to begin at Claytonville Field in Fisher County in early 2007. Here we have the opportunity to
characterize groundwater prior to CO2-injection and establish baseline conditions at Claytonville.
Methods of this study will include: (1) examination of existing analyses of saline to fresh
water samples collected within an eight-county area encompassing SACROC and Claytonville,
(2) additional groundwater sampling for analysis of general chemistry plus field-measured pH,
alkalinity, and temperature, stable isotopic ratios of hydrogen (D/H), oxygen (18O/16O), and
carbon (13C/12C), and (3) geochemical equilibrium and flowpath modeling. Existing groundwater
data are available from previous BEG studies, Texas Water Development Board, Kinder Morgan
CO2 Company, and the U. S. Geological Survey. By examining these data we will identify
regional groundwater variability and focus additional sampling efforts. The objective of this study
is to look for potential impacts to shallow groundwater from deep CO2-injection. In the absence
of conduit flow from depth, we don’t expect to see impacts to shallow groundwater, but
methodology to demonstrate this to regulators needs to be established.
This work is a subset of the Southwest Regional Partnership on Carbon Sequestration
Phase 2studies funded by the Department of Energy (DOE) in cooperation with industry and
government partners.Bureau of Economic Geolog
Toward a homogeneous set of transiting planet parameters
With 40 or more transiting exoplanets now known, the time is ripe to seek
patterns and correlations among their observed properties, which may give
important insights into planet formation, structure, and evolution. This task
is made difficult by the widely different methodologies that have been applied
to measure their properties in individual cases. Furthermore, in many systems
our knowledge of the planet properties is limited by the knowledge of the
properties of the parent stars. To address these difficulties we have
undertaken the first comprehensive analysis of the data for 23 transiting
planets using a uniform methodology. We revisit several of the recently
proposed correlations, and find new ones involving the metallicity of the
parent stars.Comment: 4 pages including figures. To appear in Proceedings of IAU Symposium
253, "Transiting Planets", May 2008, Cambridge, M
Evolution of Exoplanets and their Parent Stars
Studying exoplanets with their parent stars is crucial to understand their
population, formation and history. We review some of the key questions
regarding their evolution with particular emphasis on giant gaseous exoplanets
orbiting close to solar-type stars. For masses above that of Saturn, transiting
exoplanets have large radii indicative of the presence of a massive
hydrogen-helium envelope. Theoretical models show that this envelope
progressively cools and contracts with a rate of energy loss inversely
proportional to the planetary age. The combined measurement of planetary mass,
radius and a constraint on the (stellar) age enables a global determination of
the amount of heavy elements present in the planet interior. The comparison
with stellar metallicity shows a correlation between the two, indicating that
accretion played a crucial role in the formation of planets. The dynamical
evolution of exoplanets also depends on the properties of the central star. We
show that the lack of massive giant planets and brown dwarfs in close orbit
around G-dwarfs and their presence around F-dwarfs are probably tied to the
different properties of dissipation in the stellar interiors. Both the
evolution and the composition of stars and planets are intimately linked.Comment: appears in The age of stars - 23rd Evry Schatzman School on Stellar
Astrophysics, Roscoff : France (2013
A Time-Dependent Radiative Model of HD209458b
We present a time-dependent radiative model of the atmosphere of HD209458b
and investigate its thermal structure and chemical composition. In a first
step, the stellar heating profile and radiative timescales were calculated
under planet-averaged insolation conditions. We find that 99.99% of the
incoming stellar flux has been absorbed before reaching the 7 bar level.
Stellar photons cannot therefore penetrate deeply enough to explain the large
radius of the planet. We derive a radiative time constant which increases with
depth and reaches about 8 hr at 0.1 bar and 2.3 days at 1 bar. Time-dependent
temperature profiles were also calculated, in the limit of a zonal wind that is
independent on height (i.e. solid-body rotation) and constant absorption
coefficients. We predict day-night variations of the effective temperature of
\~600 K, for an equatorial rotation rate of 1 km/s, in good agreement with the
predictions by Showman &Guillot (2002). This rotation rate yields day-to-night
temperature variations in excess of 600 K above the 0.1-bar level. These
variations rapidly decrease with depth below the 1-bar level and become
negligible below the ~5--bar level for rotation rates of at least 0.5 km/s. At
high altitudes (mbar pressures or less), the night temperatures are low enough
to allow sodium to condense into Na2S. Synthetic transit spectra of the visible
Na doublet show a much weaker sodium absorption on the morning limb than on the
evening limb. The calculated dimming of the sodium feature during planetary
transites agrees with the value reported by Charbonneau et al. (2002).Comment: 9 pages, 8 figures, replaced with the revised versio
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