It is the case that planetary orbits change in time. I think the Earth is being nudged outward by Jupiter over time. This might give added time for life to continue as the sun heats up over the next billion years and more.
LC On Sunday, August 2, 2020 at 6:39:50 PM UTC-5 smi...@zonnet.nl wrote: > On 03-08-2020 00:35, Alan Grayson wrote: > > On Sunday, August 2, 2020 at 1:51:34 PM UTC-6, Lawrence Crowell wrote: > > > >> The periapsis or perihelion advance of Mercury is largely a result > >> of classical perturbation theory in classical mechanics. About 10% > >> of the perihelion advance could not be accounted for by perturbation > >> methods in classical mechanics. > >> > >> This has to be admired in some ways. Finding the ephemeris of > >> Mercury is tough, for the planet makes brief appearances near the > >> sun in mornings and evenings. Finding an orbital path from its > >> course across the sky is not easy. The second issue is that > >> perturbation methods in classical mechanics are difficult. These > >> were developed arduously in the 19th century and Le Verrier worked > >> on this to find the planet Neptune from the perturbed motion of > >> Uranus in 1848. These methods were worked on through the 19th > >> century. The later work of von Zeipel and Poincare were used to > >> compute the periapsis advance of Mercury, but there was this > >> persistent 43arc-sec/year that resisted these effort. > > > > You mean 43 arc-sec/CENTURY. My question is this; why don't the > > perturbations due to other bodies in our solar system ALSO cause > > radial increases in Mercury's orbital energy, to produce an outward > > expansion of its orbit, rather than just rotations of the ellipse > > characterizing its orbit? > > TIA, AG > > > There are oscillations in the orbital parameters and if resonances occur > this can lead to instabilities. Mercury is close to getting onto a > resonance with Jupiter and due to the chaotic nature of the orbital > motion of the planets, this means that there is a chance that the inner > solar system can get destabilized: > > https://www.nature.com/articles/nature08096 > > "Here we report numerical simulations of the evolution of the Solar > System over 5 Gyr, including contributions from the Moon and general > relativity. In a set of 2,501 orbits with initial conditions that are in > agreement with our present knowledge of the parameters of the Solar > System, we found, as in previous studies, that one per cent of the > solutions lead to a large increase in Mercury’s eccentricity—an increase > large enough to allow collisions with Venus or the Sun. More > surprisingly, in one of these high-eccentricity solutions, a subsequent > decrease in Mercury’s eccentricity induces a transfer of angular > momentum from the giant planets that destabilizes all the terrestrial > planets ∼3.34 Gyr from now, with possible collisions of Mercury, Mars or > Venus with the Earth." > > > "The most surprising collision is the one of Venus with the Earth, > which occurs in S468 in a five-stage process (Figs 2 and 3). The first > step is the increase in the eccentricity of Mercury, obtained through > perihelion resonance with Jupiter at 3.137 Gyr. This step is essential, > as it allows a transfer of non-circular angular momentum from the outer > planets to the terrestrial planets. The eccentricity increase > of Venus, the Earth and Mars, is then obtained through secular > resonances among the inner planets while the eccentricity of Mercury > decreases between 3.305 and 3.325 Gyr. Once Mars and the Earth > acquire large eccentricities, close encounters occur and collisions > become possible, as in S468 (Fig. 3c). In S468, the collision with > Mars does not occur, but several close encounters (Fig. 3c) lead to the > diffusion of Mars’s semi-major axis (Fig. 3b) until secular resonances > produce a decrease in the eccentricity of Mercury together with an > additional increase in the eccentricity of Venus and the Earth at about > 3.347.3 Gyr (Fig. 3c). At this point, close encounters between Venus > and the Earth occur, with several exchanges of the planets’ orbits > (Fig. 3b) before a final collision at 3.352891 Gyr (Fig. 3c)." > > Saibal > > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/d00925ab-c96d-42ce-97ee-3df032d2c9a1n%40googlegroups.com.
