418 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
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
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
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
Saturn's internal structure and carbon enrichment
No full textWe use the clathrate hydrate trapping theory to calculate the enrichments in O, N, S, Xe, Ar and Kr compared to solar in Saturn's atmosphere. For this, we calibrate our calculations using two different carbon abundance determinations that cover the domain of measurements published in recent decades: one derived from the NASA Kuiper Airborne Observatory measurements and the other obtained from the Cassini spacecraft observations. We show that these two carbon abundances imply a different minimum heavy element content for Saturn. Using the Kuiper Airborne Observatory measurement for calibration, the amount of ices accreted by Saturn is found to be consistent with current interior models of this planet. On the other hand, using the Cassini measurement for calibration leads to an ice content in the planet's envelope that is higher than the one derived from the interior models. In this case, reconciling the interior models with the amount of C measured by the Cassini spacecraft requires that significant differential sedimentation of water and volatile species has taken place in Saturn's interior during its lifetime
A Review of the in Situ Probe Designs from Recent Ice Giant Mission Concept Studies
No full textFor the Ice Giants, atmospheric entry probes provide critical measurements not attainable via remote observations. Including the 2013–2022 NASA Planetary Decadal Survey, there have been at least five comprehensive atmospheric probe engineering design studies performed in recent years by NASA and ESA. International science definition teams have assessed the science requirements, and each recommended similar measurements and payloads to meet science goals with current instrument technology. The probe system concept has matured and converged on general design parameters that indicate the probe would include a 1-meter class aeroshell and have a mass around 350 to 400-kg. Probe battery sizes vary, depending on the duration of a post-release coast phase, and assumptions about heaters and instrument power needs. The various mission concepts demonstrate the need for advanced power and thermal protection system development. The many completed studies show an Ice Giant mission with an in situ probe is feasible and would be welcomed by the international science community
Modeling the Jovian subnebula. II. Composition of regular satellite ices
No full textWe use an evolutionary turbulent model of Jupiter's subnebula to constrain the composition of ices incorporated in its regular icy satellites. We consider CO2, CO, CH4, N2, NH3, H2S, Ar, Kr and Xe as the major volatile species existing in the gas-phase of the solar nebula. All these volatile species, except CO2 which crystallized as a pure condensate, are assumed to be trapped by H2O to form hydrates or clathrate hydrates in the solar nebula. Once condensed, these ices were incorporated into the growing planetesimals produced in the feeding zone of proto-Jupiter. Some of these solids then flowed from the solar nebula to the subnebula, and may have been accreted by the forming Jovian regular satellites. We show that ices embedded in solids entering at early epochs into the Jovian subdisk were all vaporized. This leads us to consider two different scenarios of regular icy satellite formation in order to estimate the composition of the ices they contain. In the first scenario, icy satellites were accreted from planetesimals that have been produced in Jupiter's feeding zone without further vaporization, whereas, in the second scenario, icy satellites were accreted from planetesimals produced in the Jovian subnebula. In this latter case, we study the evolution of carbon and nitrogen gas-phase chemistries in the Jovian subnebula and we show that the conversions of N2 to NH3, of CO to CO2, and of CO to CH4 were all inhibited in the major part of the subdisk. Finally, we assess the mass abundances of the major volatile species with respect to H2O in the interiors of the Jovian regular icy satellites. Our results are then compatible with the detection of CO2 on the surfaces of Callisto and Ganymede and with the presence of NH3 envisaged in subsurface oceans within Ganymede and Callisto
Constraints on the Formation Regions of Comets from their D:H Ratios
No full textStudies of the D:H ratio in H2O within the Solar nebula provide a relationship between the degree of enrichment of deuterium and the distance from the young Sun. In the context of cometary formation, such models suggest that comets which formed in different regions of the Solar nebula should have measurably different D:H ratios. We aim to illustrate how the observed comets can give information about the formation regions of the reservoirs in which they originated. After a discussion of the current understanding of the regions in which comets formed, simple models of plausible formation regions for two different cometary reservoirs (the Edgeworth–Kuiper belt and the Oort Cloud) are convolved with a deuterium-enrichment profile for the pre-solar nebula. This allows us to illustrate how different formation regions for these objects can lead to great variations in the deuterium enrichment distributions that we would observe in comets today. We also provide an illustrative example of how variations in the population within a source region can modify the resulting observational profile. The convolution of a deuterium-enrichment profile with examples of proto-cometary populations gives a feel for how observations could be used to draw conclusions on the formation region of comets which are currently fed into the inner Solar system from at least two reservoirs. Such observations have, to date, been carried out on only three comets, but future work with instruments such as ALMA and Herschel should vastly improve the dataset, leading to a clearer consensus on the formation of the Oort cloud and Edgeworth–Kuiper belt
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