f704 J-M Souriau: On the dynamics of the solar system (p3)
...The surface of the Sun is lifted: therefore tidal effects exist, hence dissipative processes, whose result is the gradual wearing down of orbits, the fact that planetary trajectories—even perfectly circularized (by tidal effects)—could be spirals tending to draw planets toward the Sun and cause them to merge with it, even though the characteristic timescale for this phenomenon is considerable (not yet quantified today).
...On the other hand, it seems to me that there exist systems obeying the golden rule which no longer exchange energy with the celestial body around which they orbit. These are the asteroid belt and the rings of the large planets (Saturn, Uranus, essentially). These rings do not generate tidal effects in the central body (although Saturn’s rings are indirectly influenced by the planet through the action exerted on them by certain satellites). The ring particles of Saturn are ice blocks with nearly zero relative "self-motion." If these self-motions were significant, they could not occur in just two dimensions. Saturn’s ring would then be thick. Moreover, collisions between these blocks would shower Earth with comets, rendering it uninhabitable.
Catastrophic parenthesis.
...We do not precisely know the size of the ice blocks composing the rings, but some could well be twenty kilometers across. A block of this size, equivalent to a mountain, plunging into Earth’s atmosphere at tens of kilometers per second would create a shockwave that would encircle the planet long before the block had begun to melt.
Fig. 11: Penetration of a comet into Earth’s atmosphere.
...Upon hitting the surface, it explodes into fragments. Millions of tons of soil or rock are also transformed into fine dust. The incident shockwave reflects. It leaves behind a bubble of hot, high-temperature air. The incident shockwave propagates laterally, centrifugally, destroying everything in its path. But the crucial point is the "delay effect." This hot, lighter air rises, carrying millions of tons of dust particles, about the size of a micron, which can then remain in the stratosphere for one or two years (simply because their fall speed is very low). This dusty veil will block solar radiation.
Fig. 12: Comet night.
...Initially dispersed longitudinally, then latitudinally, due to cooling and the cessation of photosynthesis, this shield will cause the death of a large proportion of living beings, whether animals or plants.
...Our planet and the impactor, of varying degrees of severity. At the beginning of the century, a comet indeed fell in Siberia, in Tunguska. Eyewitness accounts: a flash, thunderous noise. At the site: no exotic debris. But trees had been felled, like this:
Fig. 13 (p019): Trees at the Tunguska site. .
...The fact that trees remained standing at the center is typical of an impact not caused by an object, but by the action of a shockwave preceding an object already fragmented into thousands of pieces.
...A similar phenomenon occurred in Hiroshima, where the destruction on the ground was not caused by fragments, but by a shockwave. Thus, a building located exactly at the impact point, which experienced the shockwave vertically, remained standing, while immediately adjacent buildings were flattened.
...At the Tunguska site, larch trees located directly at the impact point, if they had remained upright, would have been completely stripped bare during the passage.
...When speaking of comets, one sometimes evokes the term "dirty snowball." Indeed, there is no guarantee that this frozen, crystallized water formed hard ice, as would be the case if subjected to significant pressure forces. In a comet, a small object, cohesive and gravitational forces are extremely weak. Thus, what would reach Earth might be... a snowball the size of a mountain, falling at tens of kilometers per second. This would not prevent the formation of an extremely intense shockwave, synonymous with strong air heating during the incident phase and especially after reflection, when all kinetic energy is transformed into heat. The object itself lacks structural integrity, but what is harmful is its energy, synonymous with overpressure and thermal shock. Upon impacting the dense atmosphere, it generates its own shockwave. If the atmospheric impact is violent enough, the comet’s contact with the atmosphere is equivalent to an explosion. After the devastation caused at Tunguska by this shockwave, what followed might have resembled a hailstorm.
End of this catastrophic parenthesis.
Saturn’s rings seem to be an example of "completely relaxed" subsystems.
...On the other hand, the Neptune-Pluto subsystem, highly resonant (orbital period ratio very close to 3/2), is a dissipative structure.
...Thus, the solar system is a composite system, with some subsystems "relaxed" and others not. The resonant subsystems then possess their own stability, comparable to that of Bénard vortices or Von Kármán vortex streets.
...Personally, I believe the solar system tends generally toward a state of maximal relaxation, where all elements would follow golden rules—global (planets) or local (Saturn’s and Jupiter’s satellites). And Souriau adds that this conjecture would need to be confirmed by numerical simulations, which we are about to undertake.
Here enters an idea from my wife Claire, who has long been fascinated by the solar system problem, and who says:
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If we find in the solar system relaxed subsystems obeying a golden rule, and other resonant ones comparable to dissipative subsystems, it must be because an unknown perturbation occurred; otherwise, the solar system would be in a nearly relaxed state, with far fewer anomalies, such as:
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Earth’s presence on an orbit that is "less non-resonant"
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The existence of an asteroid belt between Mars and Jupiter
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Mercury’s relatively high orbital eccentricity
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The near absence of rings around Jupiter, despite Saturn and Uranus having them
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Earth’s metallic core and strong tectonic activity
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Pluto’s orbital inclination (18°) and Uranus’s rotational axis inclination (close to 90°)
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Significant deviations of some of Saturn’s and Jupiter’s satellites from the golden rule
...Thus, the solar system may have previously experienced a more "calm" state, disturbed by a major event. More precisely, Claire believes the perturbation occurred during the early stages of the solar system’s formation, when stars were "in the process of calming down" (tendency toward orbital circularization, formation of the ecliptic plane), and certain elements retained local traces of this phenomenon (the anomalies).
...A few years ago, the Shoemaker-Levy comet collided with Jupiter. A significant fact: before impact, recorded by a satellite (it had occurred on the far side of the planet...