1,600 research outputs found
Formation of Early Water Oceans on Rocky Planets
Terrestrial planets, with silicate mantles and metallic cores, are likely to
obtain water and carbon compounds during accretion. Here I examine the
conditions that allow early formation of a surface water ocean (simultaneous
with cooling to clement surface conditions), and the timeline of degassing the
planetary interior into the atmosphere. The greatest fraction of a planet's
initial volatile budget is degassed into the atmosphere during the end of magma
ocean solidification, leaving only a small fraction of the original volatiles
to be released into the atmosphere through later volcanism. Rocky planets that
accrete with water in their bulk mantle have two mechanisms for producing an
early water ocean: First, if they accrete with at least 1 to 3 mass% of water
in their bulk composition, liquid water may be extruded onto the planetary
surface at the end of magma ocean solidification. Second, at initial water
contents as low as 0.01 mass% or lower, during solidification a massive
supercritical fluid and steam atmosphere is produced that collapses into a
water ocean upon cooling. The low water contents required for this process
indicate that rocky super-Earth exoplanets may be expected to commonly produce
water oceans within tens to hundreds of millions of years of their last major
accretionary impact, through collapse of their atmosphere.Comment: 8 text pages with 5 figures following; Accepted at Astrophysics and
Space Scienc
Pushing It To The Edge: Extending Generalised Regression As A Spatial Microsimulation Method
This paper extends a spatial microsimulation model to test how the model behaves after adding different constraints, and how results using univariate constraint tables rather than multivariate constraint tables compare. This paper also tests how well non-Capital city households from a survey can estimate areas within capital cities. Using all households available in Australian survey means that the spatial microsimulation method has more households to choose from to represent the constraints in the area being estimated. In theory, this should improve the fit of the model. However, a household from another area may not be representative of households in the area being estimated. We found that, in the case that the estimated statistics is already closely related to the benchmarks used, adding a number of benchmarks had little effect on the number of areas where estimates couldn’t be made, and had little effect on the accuracy of our estimates in areas where estimates could be made. However, the advantage of using more benchmarks was that the weights can be used to estimate a wider variety of outcome variables. We also found that more complex bi-variate benchmarks gave better results compared to simpler univariate benchmarks; and that using a specific sub-sample of observations from a survey gave better results in smaller capital cities in Australia (Adelaide and Perth).
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Farm business survey 2009/10: horticulture production in England
Thereport gives an overview of the horticultural industry in the United Kingdom, including a snapshot of the different sectors of production, together with other information of interest about the business of horticulture. The data includes the economic perforamnce of horticulture businesses in England during 2009/1
Ranges of Atmospheric Mass and Composition of Super Earth Exoplanets
Terrestrial-like exoplanets may obtain atmospheres from three primary
sources: Capture of nebular gases, degassing during accretion, and degassing
from subsequent tectonic activity. Here we model degassing during accretion to
estimate the range of atmospheric mass and composition on exoplanets ranging
from 1 to 30 Earth masses. We use bulk compositions drawn from primitive and
differentiated meteorite compositions. Degassing alone can create a wide range
of masses of planetary atmospheres, ranging from less than a percent of the
planet's total mass up to ~6 mass% of hydrogen, ~20 mass% of water, and/or ~5
mass% of carbon compounds. Hydrogen-rich atmospheres can be outgassed as a
result of oxidizing metallic iron with water, and excess water and carbon can
produce atmospheres through simple degassing. As a byproduct of our atmospheric
outgassing models we find that modest initial water contents (10 mass% of the
planet and above) create planets with deep surface liquid water oceans soon
after accretion is complete.Comment: ApJ, in press. 32 pages, 6 figure
Coreless Terrestrial Exoplanets
Differentiation in terrestrial planets is expected to include the formation
of a metallic iron core. We predict the existence of terrestrial planets that
have differentiated but have no metallic core--planets that are effectively a
giant silicate mantle. We discuss two paths to forming a coreless terrestrial
planet, whereby the oxidation state during planetary accretion and
solidification will determine the size or existence of any metallic core. Under
this hypothesis, any metallic iron in the bulk accreting material is oxidized
by water, binding the iron in the form of iron oxide into the silicate minerals
of the planetary mantle. The existence of such silicate planets has
consequences for interpreting the compositions and interior density structures
of exoplanets based on their mass and radius measurements.Comment: ApJ, in press. 22 pages, 5 figure
Expanding the application of the Eu-oxybarometer to the lherzolitic shergottites and nakhlites: Implications for the oxidation state heterogeneity of the Martian interior
Experimentally rehomogenized melt inclusions from the nakhlite Miller Range 03346 (MIL 03346) and the lherzolitic shergottite Allan Hills 77005 (ALH 77005) have been analyzed for their rare earth element (REE) concentrations in order to characterize the early melt compositions of these Martian meteorites and to calculate the oxygen fugacity conditions they crystallized under. D(Eu/Sm)pyroxene/melt values were measured at 0.77 and 1.05 for ALH 77005 and MIL 03346,
respectively. These melts and their associated whole rock compositions have similar REE patterns, suggesting that whole rock REE values are representative of those of the early melts and can be used as input into the pyroxene Eu-oxybarometer for the nakhlites and lherzolitic shergottites. Crystallization fO_2 values of IW + 1.1 (ALH 77005) and IW + 3.2 (MIL 03346) were calculated. Whole rock data from other nakhlites and lherzolitic shergottites was input into the Eu-oxybarometer to determine their crystallization fO_2 values. The lherzolitic shergottites and nakhlites have fO_2 values that range from IW + 0.4 to 1.6 and from IW + 1.1 to 3.2, respectively. These values are consistent
with some previously determined fO_2 estimates and expand the known range of fO_2 values of the Martian interior to four orders of magnitude. The origins of this range are not well constrained. Possible mechanisms for producing this spread in fO_2 values include mineral/melt fractionation, assimilation, shock effects, and magma ocean crystallization processes. Mineral/melt partitioning can result in changes in fO_2 from the start to the finish of crystallization of 2 orders of magnitude. In addition, crystallization of a Martian magma ocean with reasonable initial water content results in oxidized, water-rich, late-stage cumulates. Sampling of these oxidized cumulates or interactions between reduced melts and the oxidized material can potentially account for the range of fO_2 values observed in the Martian meteorites
On the Emergent Spectra of Hot Protoplanet Collision Afterglows
We explore the appearance of terrestrial planets in formation by studying the
emergent spectra of hot molten protoplanets during their collisional formation.
While such collisions are rare, the surfaces of these bodies may remain hot at
temperatures of 1000-3000 K for up to millions of years during the epoch of
their formation. These object are luminous enough in the thermal infrared to be
observable with current and next generation optical/IR telescopes, provided
that the atmosphere of the forming planet permits astronomers to observe
brightness temperatures approaching that of the molten surface. Detectability
of a collisional afterglow depends on properties of the planet's atmosphere --
primarily on the mass of the atmosphere. A planet with a thin atmosphere is
more readily detected, because there is little atmosphere to obscure the hot
surface. Paradoxically, a more massive atmosphere prevents one from easily
seeing the hot surface, but also keeps the planet hot for a longer time. In
terms of planetary mass, more massive planets are also easier to detect than
smaller ones because of their larger emitting surface areas. We present
preliminary calculations assuming a range of protoplanet masses (1-10
M_\earth), surface pressures (1-1000 bar), and atmospheric compositions, for
molten planets with surface temperatures ranging from 1000 to 1800 K, in order
to explore the diversity of emergent spectra that are detectable. While current
8- to 10-m class ground-based telescopes may detect hot protoplanets at wide
orbital separations beyond 30 AU (if they exist), we will likely have to wait
for next-generation extremely large telescopes or improved diffraction
suppression techniques to find terrestrial planets in formation within several
AU of their host stars.Comment: 28 pages, 6 figures, ApJ manuscript format, accepted into the Ap
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