Interpretation of heliocentric water production rates of comets

Aims. We investigate the influence of three basic factors on water production rate as a function of heliocentric distance: nucleus shape, the spin axis orientation, and the distribution of activity on a comet's surface. Methods. We used a basic water sublimation model driven by solar insolation to derive total production rates for different nuclei shapes and spin axis orientations using the orbital parameters of 67P/Churyumov-Gerasimenko. We used known shape models derived from prior missions to the Jupiter Family and short period comets. The slopes of production rates versus heliocentric distance were calculated for the different model setups. Results. The standard (homogeneous) outgassing model confirms the well-known result regarding the heliocentric dependence of water production rate that remains invariant for different nuclei shapes as long as the rotation axis is perpendicular to the orbital plane. When the rotation axis is not perpendicular, the nucleus shape becomes a critically important factor in determining the water production curves as the illuminated cross section of the nucleus changes with heliocentric distance. Shape and obliquity can produce changes in the illuminated cross section of up to 50% over an orbit. In addition, different spin axis orientations for a given shape can dramatically alter the pre-and post-perihelion production curves, as do assumptions about the activity distribution on the surface. If, however, the illuminated cross section of the nucleus is invariant, then the dependence on the above parameters is weak, as demonstrated here with the 67P/Churyumov-Gerasimenko shape. The comets Hartley 2 and Wild 2 are shown to yield significantly different production curve shapes for the same orbit and orientation as 67P/CG, varying by as much as a factor of three as a result of only changing the nucleus shape. Finally, we show that varying just three basic parameters, shape, spin axis orientation, and active spots distribution on the surface can lead to arbitrary deviations from the expected inverse square law dependence of water production rates near 1 au. Conclusions. With the results obtained, we cannot avoid the conclusion that, without prior knowledge of basic parameters (shape, spin axis orientation, activity locations), it is difficult to reveal the nature of cometary outgassing from the heliocentric water production rates. Similarly, the inter-comparison of water production curves of two such comets may not be meaningful

Prepaid Voice Services Based on OpenBTS Platform

This article describes the design and implementation of prepaid voice services based on OpenBTS platform. By using various programming languages and open-source software tools, we can integrate prepaid voice services with this system, so its functionality is resembled as much as possible the operation of traditional GSM network provider. This article also provides description of how customers will approach their billing services, how they will access their accounts and pay their invoices

Cometary Comae-Surface Links:The Physics of Gas and Dust from the Surface to a Spacecraft

A comet is a highly dynamic object, undergoing a permanent state of change. These changes have to be carefully classified and considered according to their intrinsic temporal and spatial scales. The Rosetta mission has, through its contiguous in-situ and remote sensing coverage of comet 67P/Churyumov-Gerasimenko (hereafter 67P) over the time span of August 2014 to September 2016, monitored the emergence, culmination, and winding down of the gas and dust comae. This provided an unprecedented data set and has spurred a large effort to connect in-situ and remote sensing measurements to the surface. In this review, we address our current understanding of cometary activity and the challenges involved when linking comae data to the surface. We give the current state of research by describing what we know about the physical processes involved from the surface to a few tens of kilometres above it with respect to the gas and dust emission from cometary nuclei. Further, we describe how complex multidimensional cometary gas and dust models have developed from the Halley encounter of 1986 to today. This includes the study of inhomogeneous outgassing and determination of the gas and dust production rates. Additionally, the different approaches used and results obtained to link coma data to the surface will be discussed. We discuss forward and inversion models and we describe the limitations of the respective approaches. The current literature suggests that there does not seem to be a single uniform process behind cometary activity. Rather, activity seems to be the consequence of a variety of erosion processes, including the sublimation of both water ice and more volatile material, but possibly also more exotic processes such as fracture and cliff erosion under thermal and mechanical stress, sub-surface heat storage, and a complex interplay of these processes. Seasons and the nucleus shape are key factors for the distribution and temporal evolution of activity and imply that the heliocentric evolution of activity can be highly individual for every comet, and generalisations can be misleading

Atomic Oxygen Retrieved From the SABER 2.0- and 1.6-μm Radiances Using New First-Principles Nighttime OH( v ) Model

The recently discovered fast, multiquantum OH(v)+O(³P) vibrational‐to‐electronic relaxation mechanism provided new insight into the OH(v) Meinel band nighttime emission formation. Using a new detailed OH(v) model and novel retrieval algorithm, we obtained O(³P) densities in the nighttime mesosphere and lower thermosphere (MLT) from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) 2.0‐ and 1.6‐μm radiances. We demonstrate how critical the new OH(v) relaxation mechanism is in the estimation of the abundance of O(³P) in the nighttime MLT. Furthermore, the inclusion of this mechanism enables us to reconcile historically large discrepancies with O(³P) results in the MLT obtained with different physical models and retrieval techniques from WIND Imaging Interferometer, Optical Spectrograph and Infrared Imager System, and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography observations of other airglow emissions. Whereas previous SABER O(³P) densities were up to 60% higher compared to other measurements the new retrievals agree with them within the range (±25%) of retrieval uncertainties. We also elaborate on the implications of this outcome for the aeronomy and energy budget of the MLT region

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

On Long-Term SABER CO2 Trends and Effects Due to Nonuniform Space and Time Sampling

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the TIMED satellite has been continuously operating for more than 16 years, since 2002, monitoring the CO concentration on nearly a global scale in the middle and upper atmosphere (from 65 km up to 110 km). A recent reanalysis (Qian et al., 2017, https://doi.org/10.1002/2016JA023825) concluded that different deseasonalizing methodologies may have a strong impact on long-term trend analysis, ultimately yielding different altitude profiles of the global mean CO trend. In this work, we aim to understand how the nonuniform spatial and temporal sampling inherent in the SABER CO data set affects the determination of the long-term trends. In addition, our goal is to disentangle reported differences in SABER CO trends due to different time averaging windows and methodologies used for trend estimation. The Whole Atmosphere Community Climate Model is used for synthetic studies of the time series. We demonstrate that, due to the time varying data gaps and nonuniform sampling of local times, different time binning of the SABER CO data may indeed bias the long-term trend estimation. We show and discuss how the 60-day averaging reduces the bias in relative trends. We also conclude that different deseasonalizing methodologies (averaged over the same temporal bins) yield negligible differences on the trend determination. Taking this into account the global mean CO relative trend does not deviate statistically from the tropospheric value below 1 × 10 mb (90 km). Above about 90 km, there is a positive slope in the global CO trend profile, but with substantially reduced magnitude for 60-day binned data.©2018. American Geophysical Union. All Rights Reserved.The authors would like to acknowledge the support of the SABER retrieval team providing the version 2.0 data, including scientists from GATS, Inc., NASA Langley Research Center, NASA Goddard Space Flight Center, Spain (IAA), and Arcon, Inc. The SABER CO2 data used in this study are available to the public in the form of NetCDF files at ftp://saber.gats-inc.com/Version2_0/Level2C/. More information about WACCM can be found at https://www2.acom.ucar.edu/gcm/waccm.The SD-WACCM outputs are available on NCAR's High Performance Storage System. The MERRA data can be obtained from http://disc.sci.gsfc.nasa.gov/daac-bin/DataHoldings.pl.This research was carried out at the Hampton University and Max-Planck-Institut fur Sonnensystemforschung. L. R. acknowledges financial support from the Priority Program 1788 Dynamic Earth of the German Research Foundation (DFG). J. Y. is supported by NASA grants NNX14AF20G, NNH13ZDA001N-HGI, and NNH15ZDA001N-HSR. J. Y. is grateful to Liying Qian, Quan Gan, and Anne Smith for valuable discussions. J. Y. is also supported by the ISSI team >Climate Change in the Upper Atmosphere>. M. L.-P. has been supported by the Spanish MICINN under projects ESP2014-54362-P and ESP2017-87143-R and EC FEDER funds

Modeling the CH4 3.3 µm non-LTE emissions in Jupiter and Saturn

International audienceThe homopause divides planetary atmospheres into the high-pressure region where chemical species are well mixed by eddy diffusion and the low-pressure region where molecular diffusion separates species according to their individual masses. In Jupiter and Saturn, the homopause pressure level controls the methane abundance vertical profile, as methane is heavier than the two dominant species, H<SUB>2</SUB> and He. Methane plays a critical role in establishing the thermal structure on these planets. It is the prime near-infrared absorber that warms the Jovian and Kronian upper atmospheres, and its photolysis by solar UV radiation triggers the production of ethane, acetylene, and heavier hydrocarbons that are the prime far-infrared coolants in these upper atmospheres. Hence the homopause level drives the heating rates, and, as ethane is mainly produced by the three-body methyl recombination (2CH<SUB>3</SUB> M -> C<SUB>2</SUB>H<SUB>6</SUB> M) whose reaction rate highly varies with pressure, the homopause level also controls the cooling rates. The determination of the methane homopause level in Jupiter and Saturn through solar occultations has been notoriously difficult as different studies and authors led to different results (see Moses et al. (2004), Fouchet et al. (2009) for reviews). Greathouse et al. (2010) even suggested that the Jovian homopause might vary spatially and/or temporally. Here we present a detailed non-LTE model of CH<SUB>4</SUB> 3.3 µm emissions for Jupiter and Saturn's atmosphere. The model accounts for various mechanisms of non-thermal excitation of CH<SUB>4</SUB> molecules as well as inter- and intra-molecular vibrational-vibrational (VV) and vibrational-translational (VT) energy exchanges. With the help of this model, we studied the sensitivity of CH<SUB>4</SUB> 3.3 µm emissions to the temperature and methane abundance vertical profiles and compared integrated radiances with the corresponding Infrared Space Observatory (ISO) observations. We will discuss implications of these results to the interpretation of the homopause pressure level as well as opportunities the JWST telescope will provide to map the homopause across both planets

Modeling the CH4 3.3 µm non-LTE emissions in Jupiter and Saturn

International audienceThe homopause divides planetary atmospheres into the high-pressure region where chemical species are well mixed by eddy diffusion and the low-pressure region where molecular diffusion separates species according to their individual masses. In Jupiter and Saturn, the homopause pressure level controls the methane abundance vertical profile, as methane is heavier than the two dominant species, H<SUB>2</SUB> and He. Methane plays a critical role in establishing the thermal structure on these planets. It is the prime near-infrared absorber that warms the Jovian and Kronian upper atmospheres, and its photolysis by solar UV radiation triggers the production of ethane, acetylene, and heavier hydrocarbons that are the prime far-infrared coolants in these upper atmospheres. Hence the homopause level drives the heating rates, and, as ethane is mainly produced by the three-body methyl recombination (2CH<SUB>3</SUB> M -> C<SUB>2</SUB>H<SUB>6</SUB> M) whose reaction rate highly varies with pressure, the homopause level also controls the cooling rates. The determination of the methane homopause level in Jupiter and Saturn through solar occultations has been notoriously difficult as different studies and authors led to different results (see Moses et al. (2004), Fouchet et al. (2009) for reviews). Greathouse et al. (2010) even suggested that the Jovian homopause might vary spatially and/or temporally. Here we present a detailed non-LTE model of CH<SUB>4</SUB> 3.3 µm emissions for Jupiter and Saturn's atmosphere. The model accounts for various mechanisms of non-thermal excitation of CH<SUB>4</SUB> molecules as well as inter- and intra-molecular vibrational-vibrational (VV) and vibrational-translational (VT) energy exchanges. With the help of this model, we studied the sensitivity of CH<SUB>4</SUB> 3.3 µm emissions to the temperature and methane abundance vertical profiles and compared integrated radiances with the corresponding Infrared Space Observatory (ISO) observations. We will discuss implications of these results to the interpretation of the homopause pressure level as well as opportunities the JWST telescope will provide to map the homopause across both planets

Modeling the CH4 3.3 µm non-LTE emissions in Jupiter and Saturn

International audienceThe homopause divides planetary atmospheres into the high-pressure region where chemical species are well mixed by eddy diffusion and the low-pressure region where molecular diffusion separates species according to their individual masses. In Jupiter and Saturn, the homopause pressure level controls the methane abundance vertical profile, as methane is heavier than the two dominant species, H<SUB>2</SUB> and He. Methane plays a critical role in establishing the thermal structure on these planets. It is the prime near-infrared absorber that warms the Jovian and Kronian upper atmospheres, and its photolysis by solar UV radiation triggers the production of ethane, acetylene, and heavier hydrocarbons that are the prime far-infrared coolants in these upper atmospheres. Hence the homopause level drives the heating rates, and, as ethane is mainly produced by the three-body methyl recombination (2CH<SUB>3</SUB> M -> C<SUB>2</SUB>H<SUB>6</SUB> M) whose reaction rate highly varies with pressure, the homopause level also controls the cooling rates. The determination of the methane homopause level in Jupiter and Saturn through solar occultations has been notoriously difficult as different studies and authors led to different results (see Moses et al. (2004), Fouchet et al. (2009) for reviews). Greathouse et al. (2010) even suggested that the Jovian homopause might vary spatially and/or temporally. Here we present a detailed non-LTE model of CH<SUB>4</SUB> 3.3 µm emissions for Jupiter and Saturn's atmosphere. The model accounts for various mechanisms of non-thermal excitation of CH<SUB>4</SUB> molecules as well as inter- and intra-molecular vibrational-vibrational (VV) and vibrational-translational (VT) energy exchanges. With the help of this model, we studied the sensitivity of CH<SUB>4</SUB> 3.3 µm emissions to the temperature and methane abundance vertical profiles and compared integrated radiances with the corresponding Infrared Space Observatory (ISO) observations. We will discuss implications of these results to the interpretation of the homopause pressure level as well as opportunities the JWST telescope will provide to map the homopause across both planets