Planetary formation in the γ Cephei system Thébault, P.; Marzari, F.; Scholl, H. ...
Astronomy and astrophysics (Berlin),
12/2004, Letnik:
427, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We numerically investigate under which conditions the planet detected at 2.1 AU from γ Cephei could form through the core-accretion scenario despite the perturbing presence of the highly eccentric ...companion star. We first show that the initial stage of runaway accretion of kilometer-sized planetesimals is possible within 2.5 AU from the central star only if large amounts of gas are present. In this case, gaseous friction induces periastron alignment of the orbits which reduces the otherwise high mutual impact velocities due to the companion's secular perturbations. The following stage of mutual accretion of large embryos is also modeled. According to our simulations, the giant impacts among the embryos always lead to a core of 10 $M_{\oplus}$ within 10 Myr, the average lifetime of gaseous discs. However, the core always ends up within 1.5 AU from the central star. Either the core grows more quickly in the inner region of the disc, or it migrates inside by scattering the residual embryos.
We present wind speeds at the ~ 1 bar level at both Jovian polar regions inferred from the 5‐μm infrared images acquired by the Jupiter InfraRed Auroral Mapper (JIRAM) instrument on the National ...Aeronautics and Space Administration Juno spacecraft during its fourth periapsis (2 February 2017). We adopted the criterion of minimum mean absolute distortion (Gonzalez & Woods, 2008) to quantify the motion of cloud features between pairs of images. The associated random error on speed estimates is 12 m/s in the northern polar region and 9.8 m/s at the south. Assuming that polar cyclones described by Adriani et al. (2018, https://doi.org/10.1038/nature25491) are in rigid motion with respect to System III, tangential speeds in the interior of the vortices increase linearly with distance from the center. The annulus of maximum speed for the main circumpolar cyclones is located at approximatively 1,000 km from their centers, with peak cyclonic speeds typically between 80 and 110 m/s and ~50 m/s in at least two cases. Beyond the annulus of maximum speed, tangential speed decreases inversely with the distance from the center within the Southern Polar Cyclone and somewhat faster within the Northern Polar Cyclone. A few small areas of anticyclonic motions are also identified within both polar regions.
Key Points
Main vortices on the Jupiter polar regions are cyclones, with peak wind speeds up to 110 m/s
Maximum speeds are observed about 1,000 km from the centers of the vortices
Smaller and weaker anticyclonic areas are also identified
This work is dedicated to the application to 67P/Churyumov-Gerasimenko of a new quasi-3D approach for non-spherically shaped comet nuclei with the aim to interpret the current activity of the comet ...in terms of initial characteristics and to predict shape and internal stratification evolution of the nucleus. The model is applied to differently shaped nuclei taking into account the characteristics of Comet 67P/Churyumov-Gerasimenko deduced from observations. We focus our attention on the combined effects that shapes and obliquity have on the comet surface and sub-surface evolution. We discuss the results in terms of activity, local dust mantle formation and disruption, erosion of the surface and internal stratigraphy.
The results show that differently shaped nuclei can have different internal structures leading to different activity patterns and behaviors. Our calculations have shown that local variations in the dust and gas fluxes can be induced by the nucleus shape. The distribution of “active” areas on Comet 67P/Churyumov-Gerasimenko is different because of different shapes, reflecting the illumination conditions on the surface. These shapes can influence the structure of the inner coma, but the coma far away from the nucleus is only marginally affected by the nucleus shape. However, different comet behaviors can arise from differently shaped comet nuclei, especially in terms of local activity, surface and sub-surface characteristics and properties. The water flux local distribution is the most influenced by the shape as it is directly linked to the illumination. Irregular shapes have large shadowing effects that can result in activity patterns on the comet surface.
The effects of different pole directions are discussed to see the relations with the nucleus activity and internal structure. It is shown that the orientation of the rotation axis plays a strong role on the surface evolution of 67P/Churyumov-Gerasimenko, determining seasonal effects on the fluxes. The activity of the comet changes greatly with the nucleus obliquity leading to pre–post-perihelion differences in the activity and seasonal effects. The effects of the dust deposition and crust formation on the cometary activity have also been simulated and are discussed with respect to 67P/Churyumov-Gerasimenko observations. The dust mantling is also strongly obliquity dependent, with different surface distributions of the dust-covered regions according to the different comet pole orientations. Finally, we show that our model can reproduce the fluxes behavior near perihelion in terms of amplitude and asymmetry, and we estimate 20% of the illuminated surface to be active.
Mapping Io's Surface Composition With Juno/JIRAM Tosi, F.; Mura, A.; Lopes, R. M. C. ...
Journal of geophysical research. Planets,
November 2020, 2020-11-00, 20201101, Letnik:
125, Številka:
11
Journal Article
Recenzirano
The surface composition of Io is dominated by SO2 frost, plus other chemical species identified or proposed over the past decades by combining Earth‐based and space‐based observations with laboratory ...data. Here we discuss spectroscopic data sets of Io obtained by the Jovian InfraRed Auroral Mapper (JIRAM) spectro‐imager onboard Juno in nine orbits, spanning a 3‐year period. We display average spectral profiles of Io in the 2–5 μm range, and we use band depths derived from those profiles to map the geographic distribution of SO2 frost and other spectral features. This data set allows for an ~22% surface coverage at 58 to 162 km/px and in a broad range of latitudes. Our results confirm the broadly regional SO2‐frost trends already highlighted by Galileo/NIMS. Io's average spectral profiles as well as the mapping of the 4.47‐μm band also confirm that SO2 exists in the 32S16O18O isotopic form. Surprisingly, the mapping performed by JIRAM shows that the absorption band at 2.1 μm is unrelated to SO2 frost, while we map for the first time the depth of the 2.65‐μm band, highlighting regions enriched in this absorber, possibly H2S. JIRAM data confirm that the 3.92‐μm band, likely due to Cl2SO2, is largely related to the SO2 distribution. The correlation between Cl2SO2 and ClSO2, possibly revealed at 4.62 μm, is not equally clear. The simultaneous presence of two very weak spectral features at 4.55 and 4.62 μm suggests that nitrile compounds or tholins may also be present on the surface.
Plain Language Summary
The surface of Io is mainly covered by sulfur dioxide (SO2) frost and by other chemical species. The Jovian InfraRed Auroral Mapper (JIRAM) instrument onboard the NASA Juno spacecraft, in orbit around Jupiter, can occasionally observe the Galilean satellites through its slit spectrometer (2–5 μm range). We show average spectral profiles of Io obtained by JIRAM in a 3‐year period, mapping the geographic distribution of SO2 frost and other spectral features. Our results confirm the broadly regional SO2‐frost trends already highlighted in the past. Our data confirm that SO2 exists in multiple isotopic forms. Surprisingly, the mapping performed by JIRAM shows that the absorption band at 2.1 μm is unrelated to SO2 frost. We map for the first time the depth of the 2.65‐μm band, which might be related to hydrogen sulfide (H2S). We also highlight regions enriched in this absorber. We confirm that the 3.92‐μm band, ascribed to sulfuryl chloride (Cl2SO2), is largely correlated with the SO2 distribution. The correlation between Cl2SO2 and ClSO2, possibly revealed at 4.62 μm, is not equally clear. The simultaneous presence of two very weak spectral features at 4.55 and 4.62 μm suggests that nitrile compounds or tholins may also be present on the surface.
Key Points
We use spectra acquired by Juno/JIRAM in the range 2–5 μm over a 3‐year period, covering ~22% of Io, to map its surface composition
The 2.1‐μm band and the 2.65‐μm band are unrelated with SO2 frost but display trends possibly related to the transport of volatiles
We confirm that the 4.47‐μm band is diagnostic of 32S16O18O, and we show that ClSO2 is not everywhere linked to the abundance of Cl2SO2
It is not trivial, nowadays, to be fully aware of the impressive amount of astrophysical resources that are at hand. Virtual Observatories (VOs) were therefore created to provide a simple access to ...what astronomers look for. In this paper we focus on the original data access services developed specifically, in a VO perspective, for the “Small Bodies and Dust Node” (SBDN) in the framework of the Integrated and Distributed Information System (IDIS) initiative of the Europlanet Research Infrastructure project. We describe the scientific goals, along with the innovative technical aspects, of the tools that SBDN presently provides to the scientific community, namely the Comet Emission Lines service, and the Cosmic Dust Catalog service. In the former, an algorithm for the detection of unidentified emission lines has been implemented.
OBJECTIVE: To investigate, in a population heavily exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the possible unusual occurrence of diseases other than cancer. METHODS: Five year extension ...of the follow up of the cohort involved in the Seveso accident. Soil measurements identified three exposure zones: (A) highest contamination, (B) substantial, and (R) low but higher than background contamination. Blood TCDD measurements, although limited in number, confirmed zone exposure ranking. The 15 year mortality in the exposed cohort was compared with that of a large population in the surrounding non-contaminated territory. Relative risks (RRs) and 95% confidence intervals (95% CIs) were estimated with Poisson regression techniques. RESULTS: The already noted increased occurrence of cardiovascular deaths was confirmed, in particular in zone A, among males for chronic ischaemic heart disease (five deaths, RR 3.0, 95% CI 1.2 to 7.3), and among females for hypertensive disease (three deaths, RR 3.6, 95% CI 1.2 to 11.4) and chronic rheumatic heart disease. Novel findings were the increase of chronic obstructive pulmonary disease, most notably among males in zone A (four deaths, RR 3.7, 95% CI 1.4 to 9.9) and females in zone B (seven deaths, RR 2.4, 95% CI 1.1 to 5.1); and from diabetes, which was significantly increased in females in zone B (13 deaths, RR 1.9, 95% CI 1.1 to 3.2). In zone R, chronic ischaemic heart disease (males and females), hypertension (females), and diabetes (females) showed less pronounced, although significant excesses. CONCLUSIONS: As well as high TCDD exposure, the accident caused a severe burden of strain in the population. Both these factors might have contributed to the noted increased risks (in particular, circulatory and respiratory). The cardiovascular and immune toxicity of TCDD, as well as its complex interaction with the endocrine system, might be relevant to the explanations of these findings. These results, although not conclusive, concur with previous data in suggesting cardiopulmonary and endocrine effects in humans highly exposed to TCDD.
•The eucrites and diogenites are differentiated meteorites whose genetic link with the crust of asteroid Vesta was confirmed, together with the survival of said crust, by the NASA mission Dawn.•The ...composition of some eucrites and diogenites suggests an enrichment in water and highly-siderophile elements in the parent melt of Vesta’s crust, interpreted as the record of a late veneer.•The ages of the oldest eucrites and diogenites indicate that Vesta’s differentiation occurred early in the history of the Solar System and predates the formation of Jupiter and the other giant planets.•We explore how a late veneer can compositionally and erosionally influence Vesta’s crust in a proof-of-concept study focusing on the bombardment triggered by the formation and migration of Jupiter.•The late veneer and the erosion experienced by Vesta’s crust during the early collisional history of the asteroid can be jointly used as astrochemical constraints on the early evolution of the Solar System.
The circumsolar disc was the birthplace of both planetesimals and giant planets, yet the details of their formation histories are as elusive as they are important to understand the origins of the Solar System. For decades the limited thickness of Vesta’s basaltic crust, revealed by the link between the asteroid and the howardite-eucrite-diogenite family of meteorites, and its survival to collisional erosion offered an important constraint for the study of these processes. Some results of the Dawn mission, however, cast doubts on our understanding of Vesta’s interior composition and of the characteristics of its basaltic crust, weakening this classical constraint. In this work we investigate the late accretion and erosion experienced by Vesta’s crust after its differentiation and recorded in the composition of eucrites and diogenites and show that it offers an astrochemical window into the earliest evolution of the Solar System. In our proof-of-concept case study focusing on the late accretion and erosion of Vesta’s crust during the growth and migration of Jupiter, the water enrichment of eucrites appears to be a sensitive function of Jupiter’s migration while the enrichment in highly-siderophile elements of diogenites appears to be particularly sensitive to the size-frequency distribution of the planetesimals. The picture depicted by the enrichments created by late accretion in eucrites and diogenites is not qualitatively affected by the uncertainty on the primordial mass of Vesta. Crustal erosion, instead, is more significantly affected by said uncertainty and Vesta’s crust survival appears to be mainly useful to study violent collisional scenarios where highly energetic impacts can strip significant amounts of vestan material while limitedly contributing to Vesta’s late accretion. While our proof-of-concept case study is based on a simplified physical model and explores only a limited set of scenarios, our results suggest that the astrochemical record of the late accretion and erosion of Vesta’s crust provided by eucrites and diogenites can be used as a tool to investigate any process or scenario associated to the evolution of primordial Vesta and of the early Solar System.
The ice giant planets, Uranus and Neptune, represent an important and relatively unexplored class of planet. Most of our detailed information about them comes from fleeting looks by the Voyager 2 ...spacecraft in the 1980s. Voyager, and ground-based work since then, found that these planets, their satellites, rings, and magnetospheres, challenge our understanding of the formation and evolution of planetary systems. We also now know that Uranus-Neptune size planets are common around other stars. These are some of the reasons ice giant exploration was a high priority in NASA's most recent Planetary Science Decadal Survey. In preparation for the next Decadal Survey, NASA, with ESA participation, conducted a broad study of possible ice giant missions in the 2024–2037 timeframe. This paper summarizes the key results of the study, and addresses questions that have been raised by the science community and in a recent NASA review. Foremost amongst these are questions about the science objectives, the science payload, and the importance of an atmospheric probe. The conclusions of the NASA/ESA study remain valid. In particular, it is a high priority to send an orbiter and atmospheric probe to at least one of the ice giants, with instrumentation to study all components of an ice giant system. Uranus and Neptune are found to be equally compelling as science targets. The two planets are not equivalent, however, and each system has things to teach us the other cannot. An additional mission study is needed to refine plans for future exploration of these worlds.
•We summarize and clarify a recent survey of possible missions to Uranus and Neptune.•Sending an orbiter and atmospheric probe to one of the ice giants is a high priority.•Scientifically, Uranus and Neptune are each compelling.•Optimal launch opportunities occur within a couple years of 2030.•A focused study is needed, incorporating recent NASA and ESA programmatic decisions.
The detection and characterisation of planets younger than sim 100 Myr offer the opportunity to get snapshots of systems immediately after their formation, where the main evolutionary processes that ...sculpt mature planetary systems are still ongoing. Known infant exoplanets are currently scarce, and dedicated surveys are required to increase their number. We aim to determine the fundamental properties of the sim 35 Myr old star TOI-837 and its close-in Saturn-sized planet, and to investigate the system's formation and evolutionary history. We analysed TESS photometry and HARPS spectroscopic data, measured stellar and planetary parameters, and characterised the stellar activity. We performed population synthesis simulations to track the formation history of TOI-837\,$b$, and to reconstruct its possible internal structure. We investigated the planetary atmospheric evolution through photo-evaporation, and quantified the prospects for atmospheric characterisation with JWST. TOI-837\,$b$ has similar radius and mass to those of Saturn and $ and is on a primordial circular orbit. Population synthesis and early migration simulations suggest that the planet could have originally formed between 2 and 4 au, and have either a large and massive core, or a smaller Saturn-like core, depending on the opacity of the protoplanetary gas and on the growth rate of the core. We find that photo-evaporation produced negligible effects even at early ages (3–10 Myr). Transmission spectroscopy with JWST is very promising, and is expected to provide constraints on atmospheric metallicity and the abundances of H$_2$O, CO$_2$, and CH$_4$ molecules, and to probe the presence of refractory elements. TOI-837 offers valuable prospects for follow-up observations, which are needed for a thorough characterisation. JWST will help to better constrain the formation and evolution history of the system, and to clarify whether or not TOI-837\,$b$ is a Saturn-analogue.
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