2023-10-31 05:00:13
In these images, we look at turbulent swirls fueled by falling glass beads in water. This is our simplified model of the “neige de fer” which exists in the core of certain planets.
Ganymède – Image NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill
Some planets generate their own magnetic field through the movement of liquid metal in their cores – a process called a “dynamo” at work. on earth. Indeed, the Earth is large enough for the pressure to induce solidification. passes to the state…) of the liquid metal from the center of the core towards its periphery (The word periphery comes from the Greek peripheria which means circumference. More…), thus promoting large convection movements (Convection is a mode of energy transfer which involves a movement of…) which power the magnetic field of our planet (A planet is a celestial body orbiting around the Sun or another star of…). On the other hand, on small terrestrial planets, the pressure is too low to allow this crystallization from the center of the planet. The latter can even be reversed: it is then done from the periphery of the core, at the border with the mantle. It’s a plausible scenario for Ganymedea satellite (Satellite may refer to:) of Jupiter.
In this case, when the liquid metal crystallizes at the periphery of the core, iron flakes are formed, denser than the liquid metal. With nothing beneath their feet to hold them, they fall towards the center of the planet by gravity, and melt when they reach too high temperatures – like snow.
Turbulence generated by falling particles (in white), to better understand the interior of planets and their magnetic field.
Quentin Kriaa, Provided by the author
With our experiments, we are trying to understand what powers the dynamo movement in these small planets. One of the hypotheses is that the liquid metal is stirred up by this “snow” of solid iron flakes which fall into the liquid metal.
From the core to the lab
To model and better understand this phenomenon of “iron snow”, physics must be simplified. Crystallization and melting of the flakes are temporarily put aside, the complex shape of the flakes is approximated by a sphere, and the materials are replaced. .
So, let’s look in the laboratory at theflow generated when glass spheres (aka flakes) fall into water (aka liquid metal, of the same viscosity as water). By probing the interior of the flow using a vertical laser sheet (The vertical is a straight line parallel to the direction of gravity, given in particular by the…), our photos reveal that the fall of the glass particles, in white, does not leave the fluid indifferent: they produce turbulent clouds, with visible swirls using rhodamine, an orange dye. We observe a very similar phenomenon of turbulence (Turbulence designates the state of a fluid, liquid or gas, in which the speed…) when we put sugar in our coffee (if the beans are numerous and concentrated enough! ).
These images provide a fascinating observation: in each of the three photos, exactly 1 gram of glass spheres falls, but the larger the particles (from left to right), the smaller and more ephemeral the cloud they generate. Because it is indeed the presence of particles which fuels the turbulence; as soon as the particles escape from the vortices, they slow down before coming to rest, the viscosity of the water inevitably dissipating any movement.
The tendency of large particles to be little sensitive to vortices, and therefore to separate from them quickly, is an effect of inertia that we experience every day: outside, for a given wind speed, a small chick’s feather follows better and longer than a large pigeon feather, less sensitive to air movements. Due to this inertia, the gram of small particles is more capable of maintaining a turbulent cloud (HMS Turbulent (hull number: S 87) is a Trafalgar class vessel of seven…) by its simple sedimentation in initially still water.
For flakes, there are several ways to “force” the flow
Several previous works on iron snow have not made it possible to decide whether the flakes significantly mix the fluid during their fall, so that the study of their sedimentation has sometimes been evacuated. However, our experiments, the results of which will soon be submitted for publication, suggest that the flakes can have different behaviors that move the liquid metal, notably into a turbulent cloud.
On the other hand, this same work showed that the dynamo can come from “compositional convection”: the melting of numerous flakes at a given depth would accumulate an excess of liquid iron, denser than the rest of the liquid metal, inevitably leading to a rapid diving of this melted snow into depth – as would a sheet of water overlooking oil. This is what we will now study by making sugar snow in water, to add to our model the ingredient of the melting of the flakes, modeled by the dissolution of the sugar.
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#snows #iron #heart #moon #Jupiter
