The Dawn mission confirms earlier predictions that the asteroid 4 Vesta is differentiated with an iron-rich core, a silicate mantle and a basaltic crust, and supports the conjecture of Vesta being ...the parent body of the HED meteorites. To better understand its early evolution, we perform numerical calculations of the thermo-chemical evolution adopting new data obtained by the Dawn mission such as mass, bulk density and size of the asteroid.
We have expanded the thermo-chemical evolution model of Neumann et al. (2012) that includes accretion, compaction, melting and the associated changes of the material properties and the partitioning of incompatible elements such as the radioactive heat sources, advective heat transport, and differentiation by porous flow, to further consider convection and the associated effective cooling in a potential magma ocean. Depending on the melt fraction, the heat transport by melt segregation is modelled either by assuming melt flow in a porous medium or by simulating vigorous convection and heat flux of a magma ocean with a high effective thermal conductivity.
Our results show that partitioning of 26Al and its transport with the silicate melt is crucial for the formation of a global and deep magma ocean. Due to the enrichment of 26Al in the liquid phase and its accumulation in the sub-surface (for formation times t0<1.5 Ma), a thin shallow magma ocean with a thickness of 1 to a few tens of km forms – its thickness depends on the viscosity of silicate melt. The lifetime of the shallow magma ocean is O(104)–O(106) years and convection in this layer is accompanied by the extrusion of 26Al at the surface, resulting in the formation of a basaltic crust. The interior differentiates from the outside inwards with a mantle that is depleted in 26Al and core formation is completed within ∼0.3 Ma. The lower mantle experiences a maximal melt fraction of 45% suggesting a harzburgitic to dunitic composition. Our results support the formation of non-cumulate eucrites by the extrusion of early partial melt while cumulate eucrites and diogenites may form from the crystallising shallow magma ocean. Silicate melt is present in the mantle for up to 150 Ma, and convection in a crystallising core proceeds for approximately 100 Ma, supporting the idea of an early magnetic field to explain the remnant magnetisation observed in some HED meteorites.
•We model the thermo-chemical and structural evolution of Vesta.•Our model considers partitioning and extrusion of 26Al to the surface with the silicate melt.•A whole-mantle magma ocean on Vesta is unlikely.•A shallow sub-surface magma ocean forms due to the extrusion of early partial melt.•Our results support the early partial melt origin of the eucrites.
The Philae lander mission and science overview Boehnhardt, Hermann; Bibring, Jean-Pierre; Apathy, Istvan ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
07/2017, Letnik:
375, Številka:
2097
Journal Article
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The Philae lander accomplished the first soft landing and the first scientific experiments of a human-made spacecraft on the surface of a comet. Planned, expected and unexpected activities and events ...happened during the descent, the touch-downs, the hopping across and the stay and operations on the surface. The key results were obtained during 12-14 November 2014, at 3 AU from the Sun, during the 63 h long period of the descent and of the first science sequence on the surface. Thereafter, Philae went into hibernation, waking up again in late April 2015 with subsequent communication periods with Earth (via the orbiter), too short to enable new scientific activities. The science return of the mission comes from eight of the 10 instruments on-board and focuses on morphological, thermal, mechanical and electrical properties of the surface as well as on the surface composition. It allows a first characterization of the local environment of the touch-down and landing sites. Unique conclusions on the organics in the cometary material, the nucleus interior, the comet formation and evolution became available through measurements of the Philae lander in the context of the Rosetta mission.
This article is part of the themed issue ‘Cometary science after Rosetta’.
► Rheological properties of super-Earths are calculated based on mineral physics. ► The viscosity of mantle rock strongly increases with pressure. ► Conductive heat transfer in the lower mantle of ...super-Earths is dominant. ► Possible formation of stagnant zones in the deep mantle of super-Earths.
In the present study, the temperature- and pressure-dependent transport and thermal properties, i.e., viscosity, phonon thermal conductivity, thermal expansivity and heat capacities, as well as electronic and radiative thermal conductivities, have been derived for the mantles of super-Earths. These properties are necessary to understand the interior dynamics and the thermal evolution of those planets. We assume that the mantles consist of MgSiO3 perovskite (pv), but we discuss the effects of the post-perovskite transition, and we elaborate on an addition of periclase MgO and incorporated Fe. However, MgO is found to only significantly influence the phonon thermal conductivity – the viscosities, heat capacities and thermal expansivities of pv and MgO remain comparable. We use the Keane theory of solids, which takes into account the behavior of solid matter at the infinite pressure limit, adopt the Keane equations of state, and adjust for pv and MgO by comparison with experimental high-pressure and high-temperature data. We find the theory of the infinite pressure limit of Keane to be in excellent agreement with recent ab initio studies and experiments. To calculate the melting curve, we further use the Lindemann–Stacey scaling law and fit it to available experimental data. The best data fitting melting temperature for pv reaches 5700K at 135GPa and increases to 20,000K at 1.1TPa, corresponding to the core-mantle boundary of a 10 Earth mass super-Earth (10MEarth). We find the pv adiabatic temperature (with a potential temperature of 1700K) to reach 2570K at 135GPa and 5000K at 1.1TPa. To calculate the pressure-and temperature-dependent viscosity, we use the semi-empirical homologous temperature scaling to relate enthalpy change, and hence viscosity, to the melting temperature. We find that the resulting activation volume of pv decreases from 2.8cm3/mol at 25GPa to 1.4cm3/mol at 1.1TPa-resulting in a viscosity increase by ∼15 orders of magnitude through the adiabatic mantle of a 10MEarth planet. Furthermore, the thermal expansivity (of pv and MgO) decreases by a factor of eight, and the total thermal conductivity (phonon, radiative and electronic) of an Earth-like pv/MgO composite increases by a factor of seven through an adiabatic mantle of a 10MEarth super-Earth. At higher temperatures, i.e., for super-adiabatic temperature profiles, the electronic and radiative thermal conductivities strongly increase and dominate the conductive heat transport. All findings indicate an increase of heat transfer solely by conduction in the lower mantles of super-Earths. Thus our results disagree with Earth-biased full-mantle convection assumptions made by previous models for super-Earths, and additionally raise questions about the differentiation of massive rocky exoplanets and their ability to generate magnetic fields or sustain plate tectonics.
•We describe continental coverage and mantle water as a coupled feedback system.•We model the Earth’s evolution by including a thermal evolution model.•We find up to three fixed points of the system ...which evolve with time.•Present day Earth is found near an unstable fixed point.•The biosphere could stabilize the present day state through enhancing weathering.
A model of Earth’s continental coverage and mantle water budget is discussed along with its thermal evolution. The model links a thermal evolution model based on parameterized mantle convection with a model of a generic subduction zone that includes the oceanic crust and a sedimentary layer as carriers of water. Part of the subducted water is used to produce continental crust while the remainder is subducted into the mantle. The total length of the subduction zones is calculated from the total surface area of continental crust assuming randomly distributed continents. The mantle viscosity is dependent of temperature and the water concentration. Sediments are generated by continental crust erosion, and water outgassing at mid-oceanic ridges closes the water cycle. We discuss the strongly coupled, non-linear model using a phase plane defined by the continental coverage and mantle water concentration. Fixed points are found in the phase plane at which the rates of change of both variables are zero. These fixed points evolve with time, but in many cases, three fixed points emerge of which two are stable and an intermediate point is unstable with respect to continental coverage. With initial conditions from a Monte-Carlo scheme we calculate evolution paths in the phase plane and find a large spread of final states that all have a mostly balanced water budget. The present day observed 40% continental surface coverage is found near the unstable fixed point. Our evolution model suggests that Earth’s continental coverage formed early and has been stable for at least 1.5Gyr. The effect of mantle water regassing (and mantle viscosity depending on water concentration) is found to lower the present day mantle temperature by about 120K, but the present day mantle viscosity is affected little. The water cycle thus complements the well-known thermostat effect of viscosity and mantle temperature. Our results further suggest that the biosphere could impact the feedback cycles by its effects on continental weathering and erosion and may be the reason for the present day steady state of continental coverage and mantle water concentration.
We are at the beginning of a new era in the exploration of the outer solar system. Spacecraft have already visited each of the giant planets and made detailed observations of their major satellites. ...In 2017, the Cassini spacecraft ended its highly successful mission in the Saturnian system while the Juno mission has been investigating Jupiter since 2016. The New Horizons spacecraft revealed the Pluto/Charon system in 2015 and is now exploring the Kuiper belt. In parallel, NASA, ESA, and other international space agencies are considering the next major steps in the outer solar system exploration. Among these, the Jupiter Icy moon Explorer (JUICE), the first Large class mission of the ESA Cosmic Vision 2015-2025 campaign currently in development, will explore three satellites of the Jovian system-Ganymede, Europa and Callisto-to study the emergence of habitable worlds around gas giants. NASA is also
•We model the thermo-chemical evolution of the acapulcoite-lodranite parent body.•We fit the thermo-chronological data and the differentiation degree of meteorites.•We derive optimized parameters ...(size, formation time, etc.) for the parent body.•Final structure: Core, mantle, partially differentiated, and primordial layer.•Primitive achondritic and differentiated material on a common parent body.
The acapulcoites and lodranites are rare groups of primitive achondrites that originate from a common parent body and are of particular interest since they experienced only partial melting. We calculated thermal evolution and differentiation models of the parent body of the Acapulco-Lodran meteorite clan. The models were compared to the maximum metamorphic temperatures, differentiation degree, and thermo-chronological data available. An optimized set of parameters which fits to the data was determined: A radius of ≈ 260 km, a formation time of ≈ 1.7 Ma after CAIs and an initial temperature of ≈ 250 K. The burial depths derived are 7–13 km. The respective layers experienced minor melting and small-scale melt migration, matching the differentiation degree of the meteorites. The resulting structure has an iron core, a silicate mantle, a partially differentiated layer, and an undifferentiated outer shell. Our results indicate a larger size, an earlier formation time, and a formation closer to the sun of the parent body of acapulcoites and lodranites than typical estimates for ordinary chondritic parent bodies, consistent with a stronger thermal metamorphism. The burial depths support excavation by a single impact. The presence of core and mantle indicates that these meteorites could share a common parent body with differentiated stony and iron meteorites.
The Earth-like planets and moons in our solar system have iron-rich cores, silicate mantles, and a basaltic crust. Differentiated icy moons can have a core and a mantle and an outer water–ice layer. ...Indirect evidence for several icy moons suggests that this ice is underlain by or includes a water-rich ocean. Similar processes are at work in the interiors of these planets and moons, including heat transport by conduction and convection, melting and volcanism, and magnetic field generation. There are significant differences in detail, though, in both bulk chemical compositions and relative volume of metal, rock and ice reservoirs. For example, the Moon has a small core ~ 0.2 planetary radii (
R
P
), whereas Mercury’s is large (~ 0.8
R
P
). Planetary heat engines can operate in somewhat different ways affecting the evolution of the planetary bodies. Mercury and Ganymede have a present-day magnetic field while the core dynamo ceased to operate billions of years ago in the Moon and Mars. Planets and moons differ in tectonic style, from plate-tectonics on Earth to bodies having a stagnant outer lid and possibly solid-state convection underneath, with implications for their magmatic and atmosphere evolution. Knowledge about their deep interiors has improved considerably thanks to a multitude of planetary space missions but, in comparison with Earth, the data base is still limited. We describe methods (including experimental approaches and numerical modeling) and data (e.g., gravity field, rotational state, seismic signals, magnetic field, heat flux, and chemical compositions) used from missions and ground-based observations to explore the deep interiors, their dynamics and evolution and describe as examples Mercury, Venus, Moon, Mars, Ganymede and Enceladus.
Recent planetary space missions, new experimental data, and advanced numerical techniques have helped to improve our understanding of the deep interiors of the terrestrial planets and moons. In the ...present review, we summarize recent insights into the state and composition of their iron (Fe)-rich cores, as well as recent findings about the magnetic field evolution of Mercury, the Moon, Mars, and Ganymede. Crystallizing processes in iron-rich cores that differ from the classical Earth case (i.e., Fe snow and iron sulfide (FeS) crystallization) have been identified and found to be important in the cores of terrestrial bodies. The Fe snow regime occurs at pressures lower than that in the Earth’s core on the iron-rich side of the eutectic, where iron freezes first close to the core–mantle boundary rather than in the center. FeS crystallization, instead, occurs on the sulfur-rich side of the eutectic. Depending on the core temperature profile and the pressure range considered, FeS crystallizes either in the core center or close to the core–mantle boundary. The consequences of the various crystallizing mechanisms for core dynamics and magnetic field generation are discussed. For the Moon, revised paleomagnetic data obtained with advanced techniques suggest a peculiar history of its internal dynamo, with an early strong field persisting between 4.25 and 3.5 Ga, and subsequently a much weaker field. In addition, the long-lasting dynamo and the possible presence of an inner core, as inferred from a revised interpretation of Apollo seismic data, suggest core crystallization as a viable process of magnetic field generation for a substantial period during lunar evolution. The present-day magnetic fields of Mercury and Ganymede (if they occur on the iron-rich side of the Fe–FeS eutectic) and the related dynamo action are likely generated in the Fe snow regime and seem to be recent features. An earlier dynamo in Mercury would have been powered differently. For Mercury, MESSENGER data further suggest core formation under reducing conditions that may have resulted in an Fe–S–Si composition, further complicating the core crystallization process. Mars, with its early and strong paleo-field, likely has not yet started to freeze out an inner iron core.
MUPUS insertion device for the Rosetta mission Grygorczuk, Jerzy; Banaszkiewicz, Marek; Seweryn, Karol ...
Journal of Telecommunications and Information Technology,
06/2023
1
Journal Article
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An original mechanical device designed to insert a penetrator into a cometary nucleus in an almost gravityfree environment is described. The device comprises a hammer and a power supply system that ...stores electrical energy in a capacitor. The accumulated energy is discharged through a coil forming a part of electromagnetic circuit that accelerates the hammer. The efficiency of converting the electrical energy to kinetic energy of the hammer is not very high (amounts to about 25%), but the system is very reliable. Additionally, the hammer energy can be chosen from four power settings, hence adjustment of the stroke’s strength to nucleus hard- ness is possible. The device passed many mechanical, func- tional, thermal and vibration tests and was improved from one model to another. The final, flight model was integrated with the lander Philae and started its space journey to comet Churyumov-Gerasimenko in March 2004.
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