Simulation of stellar instabilities with vastly different timescales using domain decomposition

Strange mode instabilities in the envelopes of massive stars lead to shock waves, which can oscillate on a much shorter timescale than that associated with the primary instability. The phenomenon is studied by direct numerical simulation using a, with respect to time, implicit Lagrangian scheme, which allows for the variation by several orders of magnitude of the dependent variables. The timestep for the simulation of the system is reduced appreciably by the shock oscillations and prevents its long term study. A procedure based on domain decomposition is proposed to surmount the difficulty of vastly different timescales in various regions of the stellar envelope and thus to enable the desired long term simulations. Criteria for domain decomposition are derived and the proper treatment of the resulting inner boundaries is discussed. Tests of the approach are presented and its viability is demonstrated by application to a model for the star P Cygni. In this investigation primarily the feasibility of domain decomposition for the problem considered is studied. We intend to use the results as the basis of an extension to two dimensional simulations.Comment: 15 pages, 10 figures, published in MNRA

The century of the incomplete revolution: searching for general relativistic quantum field theory

In fundamental physics, this has been the century of quantum mechanics and general relativity. It has also been the century of the long search for a conceptual framework capable of embracing the astonishing features of the world that have been revealed by these two ``first pieces of a conceptual revolution''. I discuss the general requirements on the mathematics and some specific developments towards the construction of such a framework. Examples of covariant constructions of (simple) generally relativistic quantum field theories have been obtained as topological quantum field theories, in nonperturbative zero-dimensional string theory and its higher dimensional generalizations, and as spin foam models. A canonical construction of a general relativistic quantum field theory is provided by loop quantum gravity. Remarkably, all these diverse approaches have turn out to be related, suggesting an intriguing general picture of general relativistic quantum physics.Comment: To appear in the Journal of Mathematical Physics 2000 Special Issu

Four Dimensional CFT Models with Rational Correlation Functions

Recently established rationality of correlation functions in a globally conformal invariant quantum field theory satisfying Wightman axioms is used to construct a family of soluble models in 4-dimensional Minkowski space-time. We consider in detail a model of a neutral scalar field $\phi$ of dimension 2. It depends on a positive real parameter c, an analogue of the Virasoro central charge, and admits for all (finite) c an infinite number of conserved symmetric tensor currents. The operator product algebra of $\phi$ is shown to coincide with a simpler one, generated by a bilocal scalar field $V(x_1,x_2)$ of dimension (1,1). The modes of V together with the unit operator span an infinite dimensional Lie algebra $L_V$ whose vacuum (i.e. zero energy lowest weight) representations only depend on the central charge c. Wightman positivity (i.e. unitarity of the representations of $L_V$) is proven to be equivalent to $c \in N$.Comment: 28 pages, LATEX, amsfonts, latexsym. Proposition 2.3, and Conjecture in Sec. 6 are revised. Minor errors are correcte

Phobos Environment Model and Regolith Simulant for MMX Mission

Phobos and Deimos, the two moons of Mars, are considered to be scientifically important and potential human mission's target. Martian Moons eXplorer (MMX) is the JAXA's mission to explore Phobos (and/or Deimos), which is scheduled to be launched in 2024. The main spacecraft of MMX will perform in-situ observations of both Phobos and Deimos, land on one of them (most likely, Phobos), and bring samples back to Earth. Small landing modules may be included in the mission as for the Hayabusa-2 mission. The designs of both the landing and sampling devices depend largely on the surface conditions of the target body and on how this surface reacts to an external action in the low gravity conditions of the target. Thus, the Landing Operation Working Team (LOWT) of MMX, which is composed of both scientists and engineers, is studying Phobos' surface based on previous observations and theoretical/experimental considerations. Though engineering motivation initiated this activity, the results will be extremely useful for scientific purposes

Potential effects of atmospheric collapse on Martian heat flow and application to the InSight measurements

Heat flow is an important constraint on planetary formation and evolution. It has been suggested that Martian obliquity cycles might cause periodic collapses in atmospheric pressure, leading to corresponding decreases in regolith thermal conductivity (which is controlled by gas in the pore spaces). Geothermal heat would then build up in the subsurface, potentially affecting present–day heat flow — and thus the measurements made by a heat–flow probe such as the InSight HP3 instrument. To gauge the order of magnitude of this effect, we model the diffusion of a putative heat pulse caused by thermal conductivity changes with a simple numerical scheme and compare it to the heat–flow perturbations caused by other effects. We find that an atmospheric collapse to 300 Pa in the last 40 kyr would lead to a present–day heat flow that is up to larger than the average geothermal background. Considering the InSight mission with expected error bars on the HP3 measurement, this perturbation would only be significant in the best-case scenario of full instrument deployment, completed measurement campaign, and a well–modelled surface configuration. The prospects for detecting long-term climate perturbations via spacecraft heat–flow experiments remain challenging

How large are present-day heat flux variations across the surface of Mars?

International audienc

Analogue simulation of the temperature response of Mars surfaces to Phobos transits, and vice-versa

The objective of this series of experiments was to support the data interpretation of short period changes in insolation of planetary bodies such as solar eclipses or transits. The temperature response of Martian regolith to the transit of Phobos has been observed by InSight and interpreted in terms of layering in the near surface [Mueller et al. 2021]. Current and future mission may observe similar transits if a suitable thermal infrared instrument is available. An opportunity to observe a similar event with the roles of Mars and Phobos switched may be the rover on the Martian Moons eXplorer (MMX) carrying the Mini-RAD radiometer [Ulamec et al. 2023]. The original mission plan did not foresee a landing on the Mars facing side, but in case the plan is revised due to the changing launch date there might be a chance. There are however open questions about the interpretation of such observations using 1D models of heat conduction [e.g. Mueller et al. 2021]. These models assume that the subsurface is a continuum, while in reality the material consists of particles that are not necessarily small compared to the characteristic depth scale (skin depth) of the material responding to the changes in insolation. The Planetary Ices Laboratory has the necessary equiment to recreate such events on Earth in form of a thermal vacuum chamber and a solar simulator (Fig. 1). The chamber walls can be cooled with liquid nitrogen and a window with mirror on the chamber ceiling allows illumination of an approximately 15 cm diameter spot by the solar simulator. For our test set-up we have placed a tray of about 38x18x2cm filled with regolith analogue material in the center of the chamber (Fig. 2) i.e. encompassing the illuminated spot. The radiometer is set up within the chamber on a rotary stage that allows to move the Field of View of the instrument along the long axis of the tray. The FoV is small enough to fall within the illuminated spot and the rotary stage allows adjustments within the running setup. A small TIR camera also observed the tray. This instrument has lower temperature resolution but provides data on temperature inhomogeneity of the sample. The general approach of simulating the eclipses was to first evacuate the chamber, either refill with 5 mbar CO2 or to leave at <1e-4 mbar, to cool the chamber to below -60 °C, then to illuminate the regolith analogue material until the temperature approaches an equilibrium. After that the solar simulator shutter is closed for a certain duration to simulate an eclipse. This is a more abrupt change in insolation than in reality, however the purpose of these tests is to explore the limits to which our 1-D heat conduction models, that are based on the continuum assumption, can reproduce the response of materials where the layer thicknesses are not large compared to the particle sizes. For this the duration of the insolation excursion is much more important than the shape of the excursion, because the duration governs the depth to which the temperature response extends. The simple on-off state of the insolation will simplify the model calculations. During our time at the planetary ices lab we conducted 8 different tests, consisting of 4 different material configurations and 2 different pressures, corresponding to Mars and space. The first configuration consists of 2-4 mm Mojave Mars Simulant (MMS) filling the tray to a depth of 2 cm. This is intended to correspond to the deeper layers of Mars Regolith. In reality the particle size distribution of regolith is wider but we chose the coarser material to achieve a greater contrast between the layers in the following. The next configuration distributes MMS sieved to < 100 µm over the coarse material. The volume was chosen to correspond to 2 – 3 monolayers at this particle size. This material was chosen to represent airborne Martian dust that is continually removed by dust devils (or, infrequently, by landing rockets) and resettles during the dusty season and dust storms. The next configuration adds about 3 mm more dust by extending the rim of the tray and filling the tray to the new height. This was chosen as an example of a thicker dust layer. Finally, there is a concern that larger clasts (~cm), which can be expected to fill a significant fraction of the FoV, may affect the data inversion, as they cannot be easily modeled using a 1D model. To this end we added such clasts on top of the dust layer. The eclipses followed a sequence of durations that (with exceptions) were 5 sec, 10 sec, 20 sec, 40 sec, 120 sec. For cases where the top layer thermal conductivity was very low we extended the last eclipse to 240 sec. After each eclipse the insolation was left on for at least 3 times the eclipse durations so that temperatures could return to near the pre-eclipse values. The temperature response of the different durations extends to different depths an therefore may sense different layers with different thermophysical properties. The surface temperature was observed using a space qualified radiometer using a thermopile with a spectral bandpass from 8-14 µm at a sampling frequency of 1 Hz. The initial data analysis shows the effect of layering, but for a more complete evaluation the exact test conditions (chamber and sample temperature, solar simulator power) will have to be included in 1 D heat conduction models that are work in progress. Fitting these data under these well known conditions (boundary conditions, material properties) will show how accurate 1D continuum models are for the interpretation of short term changes in insolation such as transits. Depending on the results we will re-evaluate the interpretation of the InSight data

Phobos Regolith Simulant for MMX Mission: Spectral Measurement for Remote Target Identification and Deconvolution System Training

The two natural satellites of Mars, Phobos and Deimos are both important targets for scientific investigation. The JAXA mission Martian Moons eXplorer (MMX) is designed to explore Phobos and Deimos, with a launch date scheduled for 2024. The MMX spacecraft will observe both Martian moons and will land on one of them (Phobos, most likely), to collect a sample and bring it back to Earth. The designs of both the landing and sampling devices depend largely on the surface properties of the target body and on how its surface is reacting to an external action in the low gravity conditions of the target. The Landing Operation Working Team (LOWT) of MMX started analyzing previous observations and theoretical/experimental considerations to better understand the nature of Phobos surface material, developing a Phobos regolith simulant material for the MMX mission [1]. At the Institute for Planetary Research of the German aerospace Center (DLR) in Berlin we performed a spectral characterization of the Phobos regolith simulant. Those data will be used to train an Artificial Neural Network (NN) to produce a system that could rapidly classify data during the mission and for endmember decomposition

Macro-Porosity and Grain Density of C-Type Asteroid (162173) Ryugu

The Macroporosity of (162173) Ryugu is estimated based on the observed boulder size-frequency distribution

Planetary polar explorer – the case for a next-generation remote sensing mission to low Mars orbit

We propose the exploration of polar areas on Mars by a next-generation orbiter mission. In particular, we aim at studying the seasonal and regional variations in snow-deposits, which – in combination with measurements of temporal variations in rotation and gravity field – will improve models of the global planetary CO2 cycle. A monitoring of polar scarps for rock falls and avalanche events may provide insights into the dynamics of ice sheets. The mapping of the complex layering of polar deposits, believed to contain an important record of climate history, may help us understand the early climate collapse on the planet. Hence, we propose an innovative next-generation exploration mission in polar circular Low Mars Orbit, which will be of interest to scientists and challenging to engineers alike. Schemes will be developed to overcome atmosphere drag forces acting upon the spacecraft by an electric propulsion system. Based on the experience of missions of similar type in Earth orbit we believe that a two-year mission in circular orbit is possible at altitudes as low as 150 km. Such a mission opens new opportunities for novel remote sensing approaches, not requiring excessive telescope equipment or power. We anticipate precision altimetry, powerful radars, high-resolution imaging, and magnetic field mapping