280 research outputs found
Effects of Nitrogen Photoabsorption Cross Section Resolution on Minor Species Vertical Profiles in Titan's Upper Atmosphere
The significant variations in both measured and modeled densities of minor species in Titan's atmosphere call for the evaluation of possible influencing factors in photochemical modeling. The effect of nitrogen photoabsorption cross section selection on the modeled vertical profiles of minor species is analyzed here, with particular focus on C2H6 and HCN. Our results show a clear impact of cross sections used on all neutral and ion species studied. Affected species include neutrals and ions that are not primary photochemical products, including species that do not even contain nitrogen. The results indicate that photochemical models that employ low-resolution cross sections may significantly miscalculate the vertical profiles of minor species. Such differences are expected to have important implications for Titan's overall atmospheric structure and chemistry.NASA Outer Planet Research program NNH12ZDA001NInstitute for Computational Engineering and Sciences (ICES
Photochemistry and Haze Formation
One of the many exciting revelations of the New Horizons flyby of Pluto was
the observation of global haze layers at altitudes as high as 200 km in the
visible wavelengths. This haze is produced in the upper atmosphere through
photochemical processes, similar to the processes in Titan's atmosphere. As the
haze particles grow in size and descend to the lower atmosphere, they coagulate
and interact with the gases in the atmosphere through condensation and sticking
processes that serve as temporary and permanent loss processes. New Horizons
observations confirm studies of Titan haze analogs suggesting that
photochemically produced haze particles harden as they grow in size. We outline
in this chapter what is known about the photochemical processes that lead to
haze production and outline feedback processes resulting from the presence of
haze in the atmosphere, connect this to the evolution of Pluto's atmosphere,
and discuss open questions that need to be addressed in future work
A Hybrid Approach to Mining Conditions
Text mining pursues producing valuable information from natural language text. Conditions cannot be neglected because it may easily lead to misinterpretations. There are naive proposals to mine con ditions that rely on user-defined patterns, which falls short; there is only one machine-learning proposal, but it requires to provide specific-purpose dictionaries, taxonomies, and heuristics, it works on opinion sentences only, and it was evaluated very shallowly. We present a novel hybrid approach that relies on computational linguistics and deep learning; our experiments prove that it is more effective than current proposals in terms of F1 score and does not have their drawbacks
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Characterization of the Subsurface of 67P/Churyumov-Gerasimenko's Abydos Site
We investigate the structure of the subsurface of the Abydos site using a cometary nucleus model with parameters adapted to comet 67P/Churyumov-Gerasimenko and the Abydos landing site. We aim to compare the production rates derived from our model with those of the main molecules measured by Ptolemy. This will allow us to retrieve the depths at which the different molecules still exist in solid form
Isotope Geochemistry for Comparative Planetology of Exoplanets
Isotope geochemistry has played a critical role in understanding processes at work in and the history of solar system bodies. Application of these techniques to exoplanets would be revolutionary and would allow comparative planetology with the formation and evolution of exoplanet systems. The roadmap for comparative planetology of the origins and workings of exoplanets involves isotopic geochemistry efforts in three areas: (1) technology development to expand observations of the isotopic composition of solar system bodies and expand observations to isotopic composition of exoplanet atmospheres; (2) theoretical modeling of how isotopes fractionate and the role they play in evolution of exoplanetary systems, atmospheres, surfaces and interiors; and (3) laboratory studies to constrain isotopic fractionation due to processes at work throughout the solar system
Solar wind interaction with comet 67P: impacts of corotating interaction regions
International audienceWe present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1–2.7 AU from the Sun and the neutral outgassing rate ∼1025–1026 s−1, the CIRs significantly influence the cometary plasma environment at altitudes down to 10–30 km. The ionospheric low-energy (∼5 eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below −20 V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (∼10–100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2–5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events
Spatial distribution of low-energy plasma around 2 comet 67P/CG from Rosetta measurements
International audienceWe use measurements from the Rosetta plasma consortium (RPC) Langmuir probe (LAP) and mutual impedance probe (MIP) to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e. the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be ∼1-2·10 −6 , at a cometocentric distance of 10 km and at 3.1 AU from the sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisonless plasma within 260 km from the nucleus falls of with radial distance as ∼1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet
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