161,363 research outputs found
Formation of Jupiter's envelope from supersolar gas in the protoplanetary disk
No full textInternational audienceThe formation mechanism of Jupiter is still uncertain, as multiple volatile accretion scenarios can reproduce its metallicity [1-4]. The Galileo mission allowed in situ measurements of the abundances of several elements (Ar, Kr, Xe, C, N, S and P), which exhibit a uniform enrichment of 2 to 5 times the protosolar abundance, and a subsolar abundance has been measured for O. Recent measurements for N and O by the Juno mission confirmed the supersolar abundance of N, but indicated that the abundance of O may also be supersolar [5]. Elemental abundances measured in the Jupiter's atmosphere are key ingredients to trace the origin of various species.Here, we investigate the possible timescale and location of Jupiter's formation using measurements of molecular and elemental abundances in its envelope. To do so, we use a 1D accretion disk model to compute the properties of the protosolar nebula (PSN) that includes radial transport of trace species, present in the form of refractory dust, a mixture of ices and their vapors, to compute the composition of the PSN [6]. We focus on the radial transport of volatile species by advection-diffusion combined with the effect of icelines, computed as sublimation/condensation rates. Initialy, the disk is uniformly filled with H2O, PH3, CO, CO2, CH4, CH3OH, NH3, N2, H2S, Ar, Kr and Xe [6,7], corresponding to the main bearers of C, N, O, P, S, Ar, Kr and Xe.As the PSN evolves, solid particles drift inward due to gas drag. Volatile species are thus efficiently transported to their respective icelines, where they sublimate. This results in supersolar abundances of volatile elements in the inner part of the PSN. We find that the composition of Jupiter's envelope can be achieved by accretion of enriched gas only, or a mixture of gas and solids, depending on the viscosity of the PSN. In both cases, the composition of the PSN matches the one measured in Jupiter's envelope in timescale that are compatible with a formation by core accretion or gravitational collapse.[1] Gautier, D., Hersant, F., Mousis, O., et al. 2001, ApJL, 550, L227.[2] Mousis, O., Ronnet, T., and Lunine, J. I. 2019, ApJ, 875, 9.[3] Öberg, K. I. and Wordsworth, R. 2019, AJ, 158, 194.[4] Miguel, Y., Cridland, A., Ormel, C. W., et al. 2020, MNRAS, 491, 1998.[5] Li, C., Ingersoll, A., Bolton, S., et al. 2020, Nature Astronomy, 4, 609.[6] Aguichine, A., Mousis, O., Devouard, B., and Ronnet, T. 2020, ApJ, 901, 97.[7] Lodders, K., Palme, H., & Gail, H.-P. 2009, Landolt Börnstein, 4B, 71
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Reproducing the composition of Jupiter's envelope from the gas phase of the protosolar nebula
No full textInternational audienceTwo decades ago, the Galileo probe performed an in situ measurement of elemental abundances in Jupiter's atmosphere, which resulted in a number of formation scenarios to explain observations [1-4]. These measurements indicated that volatile abundances of C, N, S, P, Ar, Kr and Xe were enhanced by a factor of 2 to 6 times their protosolar value, except for O that was found to be subsolar. The more recent measurements made by Juno confirmed the supersolar abundance of N, but found that a supersolar abundance of O is possible [5]. This result calls for an update of existing models and formation theories. Here, we investigate the possibility of reproducing the composition of Jupiter's envelope in the protosolar nebula (PSN).To do so, we compute the evolution of the PSN using a 1D viscous accretion disk model [6,7]. The disk is initially uniformly filled with trace species with protosolar abundances, present in the form of dust and ice grains, and their vapor. The radial transport of trace species is computed by solving an advection-diffusion equation, and phase transitions are accounted for by computing sublimation and condensation rates for each species. We then compare the composition of the PSN computed by our model with the updated measurements of elemental abundance in Jupiter.The figure below represents profiles of the H2O abundance in the disk, normalized to its initial value, at different times of the disk evolution. Solid and dashed lines are used to indicate locations where the disk is dominated by solids (solid lines) or vapor (dashed lines). The blue box corresponds to the measurement of H2O to protosolar O abundance measured in Jupiter's atmosphere by Juno [5]. Every trace species evolves in a similar fashion, but their icelines are at different heliocentric distances.We find that the composition of Jupiter's envelope can be explained only from its accretion from PSN gas or from a mixture of vapors and solids, depending on the turbulence level in the disk. Such compositions can be found at ~4 AU, namely between the icelines of H2O (3.5 AU) and CO2 (5.5 AU), and at times 100-300 kyr of the disk evolution. These results [7] are compatible with both the core accretion model and the gravitational collapse model, but give a new possible scenario of Jupiter's formation. [1] Gautier, D., Hersant, F., Mousis, O., et al. 2001, ApJL, 550, L227.[2] Mousis, O., Ronnet, T., and Lunine, J. I. 2019, ApJ, 875, 9.[3] Öberg, K. I. and Wordsworth, R. 2019, AJ, 158, 194.[4] Miguel, Y., Cridland, A., Ormel, C. W., et al. 2020, MNRAS, 491, 1998.[5] Li, C., Ingersoll, A., Bolton, S., et al. 2020, Nature Astronomy, 4, 609.[6] Aguichine, A., Mousis, O., Devouard, B., and Ronnet, T. 2020, ApJ, 901, 97.[7] Aguichine, A., Mousis, O., and Lunine, J. I. 2022, accepted in PSJ
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
Interior structure and possible existence of irradiated ocean planets
No full textInternational audienceWater-rich planets should be ubiquitous in the universe, and could represent a notable fraction of the sub-Neptune population. Among the detected exoplanets that have been characterized as sub-Neptunes, many are subject to important irradiation from their host star. As a consequence, hydrospheres of such planets are not in condensed phase, but are rather in supercritical state, with steam atmospheres on top. Such irradiated ocean planets (IOP) are good candidates to explain the distribution of masses and radii in the sub-Neptune category of exoplanets [1]. Here, we present the IOP model that computes the structure of water-rich planets that have high irradiation temperatures. The IOP model [2] combines two models in a self-consistent way: one for the interior structure, and one for the steam atmosphere. The interior structure model [3] contains several refractory layers (iron core and rocky mantle), and on top of them an hydrosphere with an up to date equation of state (EOS) with a validity range that extends to the plasma regime. The atmosphere model [4] connects the top of the interior model with the host star by solving equations of radiative transfer.Our model has been applied to the GJ 9827 system as a test case and indicates Earth- and Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction of ∼20 ± 10%. We also compute mass-radius relationships for IOP and their analytical expression, which can be found in [2]. This allows one to directly retrieve a wide range of planetary compositions, without the requirement to run the model.Due to their high irradiation temperatures, sub-Neptunes are expected to be subject to strong atmospheric escape. This supports the idea that a massive hydrosphere could be the remnant of a complete loss of an H-He envelope. The stability of hydrospheres themselves is discussed as well [5]. Figure 1. Mass-radius relationships produced by our model (green, yellow and red thick lines) [2], compared to mass-radius relationships of planets with only condensed phases and no atmosphere (black, grey and light blue thin lines). A few planets of the solar system, the GJ-9827 system and the TOI-178 system are represented as well. Shaded regions correspond to important atmospheric loss by Jeans escape (H and H2O), or hydrodynamic escape. [1] Mousis, O., Deleuil, M., Aguichine, A., et al. 2020, ApJL, 896, L22.[2] Aguichine, A., Mousis, O., Deleuil, M., et al. 2021, ApJ, 914, 84A.[3] Brugger, B., Mousis, O., Deleuil, M., et al. 2017, ApJ, 850, 93.[4] Marcq, E., Baggio, L., Lefèvre, F., et al. 2019, Icarus, 319, 491M.[5] Vivien, H., Aguichine, A., Mousis, O., et al. 2022, accepted in ApJ
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Reference Model Payload for Ice Giant Entry Probe Missions
No full textInternational audienceDescent probes afford the opportunity to make essential atmospheric measurements that are beyond the reach of remote sensing, including the atmospheric abundances of noble gases and key isotopes, and the structure of the atmosphere beneath the cloud tops. Measurements are defined as Tier 1, representing threshold science required to justify the probe mission, and Tier 2 representing valuable science that significantly complement and enhance the threshold measurements, but of themselves are not sufficient to justify the mission. Tier 1 measurements comprise atmospheric noble gas abundances including helium, key noble gas isotope ratios, and the thermal structure of the atmosphere. Instrumentation required to achieve the Tier 1 measurements include a mass spectrometer, a helium abundance detector, and an atmospheric structure instrument comprising both sensors for pressure, temperature, and atmospheric acoustic properties (speed of sound). Tier 1 science can be achieved with a probe making measurements near one to several bars. Tier 2 science includes measurements of key isotopic ratios, the abundances of atmospheric condensables and disequilibrium species, atmospheric dynamics, the net radiative flux transfer profile of the atmosphere, and the location, composition, properties, and structure of the clouds. To achieve all the Tier 2 science objectives requires a probe descending through at least ten bars carrying the full Tier 1 suite of instruments as well as a nephelometer, net flux radiometer, and an ultrastable oscillator to enable Doppler wind tracking of the probe throughout descent
Determining the origin of the building blocks of the Ice Giants based on analogue measurements from comets
No full textInternational audienceThe abundances of the heavy elements and isotopic ratios in the present atmospheres of the giant planets can be used to trace the composition of volatiles that were present in the icy solid material that contributed to their formation. The first definitive measurements of noble gas abundances and isotope ratios at comet 67P/Churyumov-Gerasimenko (67P/C-G) were recently published by Marty et al. (2017) and Rubin et al. (2018, 2019). The implications of these abundances for the formation conditions of the 67P/C-G building blocks were then evaluated by Mousis et al. (2018a). We add here an analysis of the implications of these results for understanding the formation conditions of the building blocks of the Ice Giants and discuss how future measurements of Ice Giant atmospheric composition can be interpreted. We first evaluate the best approach for comparing comet observations with giant planet composition, and then determine what would be the current composition of the Ice Giant atmospheres based on four potential sources for their building blocks. We provide four scenarios for the origin of the Ice Giants building blocks based on four primary constraints for building block composition: (1) the bulk abundance of carbon relative to nitrogen, (2) noble gas abundances relative to carbon and nitrogen, (3) abundance ratios Kr/Ar and Xe/Ar, and (4) Xe isotopic ratios. In situ measurements of these quantities by a Galileo-like entry probe in the atmosphere(s) of Uranus and/or Neptune should place important constraints on the formation conditions of the Ice Giants
Formation of Titan in Saturn's subnebula: constraints from Huygens probe measurements
No full textWe present an evolutionary turbulent model of the Saturn's subnebula consistent with recent core accretion formation models of Saturn. Our calculations are similar to those conducted in the case of the Jovian subnebula, and take into account the vertical structure of the disk, as well as the evolution of its surface density, as given by an α-disk model. Using the thermodynamic conditions of our model, we calculate the evolution of the CO2:CO:CH4 and N2:NH3 molar mixing ratios in the subnebula. We thus show that the carbon and nitrogen homogeneous gas-phase chemistry is inhibited in the subnebula. We also consider the role played by Fischer-Tropsch catalysis in the gas-phase conversions of CO and CO2 into CH4. We demonstrate that, even if a catalytically active zone is likely to exist in the early Saturn's subnebula, it does not alter the composition of volatiles ultimately trapped in the forming solids. We study two different formation scenarios of Titan. In each scenario, we provide observational tests that are compared with measurements made by the Huygens probe. In the first scenario, Titan is formed in a late and cold subnebula from planetesimals produced in Saturn's feeding zone that have been preserved from vaporization. In the second scenario, Titan is formed in a balmy and early subnebula. We show that the first scenario predicts a CO:CH4 molar mixing ratio orders of magnitude larger than the observed one in the atmosphere of Titan, and requires strong variations of water abundance in the solar nebula on short lengthscales, whose origin is not explained. On the contrary, the second scenario does not require such large variations of the abundance of water, and predicts abundances of volatile species in Titan similar to the observed ones
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