Earth's axis is tilted 24 degrees and precesses 360 degrees drawing a circle in the heavens every 26,000 years.
This moving overhead circle is known as the precession of the equinox. There is a point where the Earth's polar axis, the orbital plane and the equatorial plane intersect. The orbit of the Earth around the Sun if viewed from above is counter clockwise as is the Earths spin making the Sun appear to rise in the East and set in the West, however, the precession of the axis is clockwise. This animation makes it easy to understand. |
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Earth's poles not only precess backwards relative to its spin and orbit but they also wobble or oscillate every 41,000 years (AKA Milankovitch cycle) so the horizontal circle drawn by its ecliptic plane is not a clean circle, rather, its more of an oscillating wavy circle which also contains wiggles.
Earth also nutates which means it wiggles while it wobbles. |
Axial Tilt (Obliquity)
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Axial Spin (Precession)
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Oval Orbit (Eccentricity)
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Wiki Quote on Milankovitch cycles
The angle of the Earth's axial tilt with respect to the orbital plane (the obliquity of the ecliptic) varies between 22.1° and 24.5°, over a cycle of about 41,000 years. (A two degree axial oscillation matching the frequency of Milankovitch weather cycle) The current tilt is 23.44°, roughly halfway between its extreme values. The tilt last reached its maximum in 8,700 BCE. It is now in the decreasing phase of its cycle, and will reach its minimum around the year 11,800 CE. Bear with me, I'm getting to the point. |
On Pluto the polar axis is tilted 120 degrees, Earth's axial tilt is 23.5 degrees.
Pluto's Milankovitch cycles oscillate up and down 24 degrees, Earth's is merely 2 degrees. Pluto's eccentricity is 0.2488 while Earth's is a mere 0.0167. The conditions that create Milankovitch weather oscillation cycles on Pluto are extreme compared to Earth and Earth's cycles drive us into and out of ice ages. The small changes in Earth's orbit, tilt and preccesion are enough to turn Earth into an ice ball or blazing hot wasteland. Consider how much more extreme the climatic changes would be on Pluto. As Pluto's pole oscillates or wobbles 24 degrees, it torques on Charon and the equatorially aligned smaller satellites and a circular stress in the form of a rotating tidal bulge is felt encompassing Sputnik Planitia at zero degrees latitude and 180 longitude. |
As Pluto's north pole experiences its 24 degree wobble cycle it also has to turn Charon's poles such that the two maintain their polar alignment.
This torquing twisting effect will generate tidal heat energy at the central point between the two planets. Since they are tidally locked and their poles wobble 24 degrees a circle of tidal flex energy (wandering bulge) would occur focused directly at the Charon and anti Charon point. Since these two planets are so close to each other in size and distance the torque stress forces are relatively extreme, at least enough to energetically take nitrogen to its triple point. |
<<<<<<<< I took this topographical map by F. Nimmo which has a small black X indicating the center of Sputnik Planitia at 18 degrees north, 175 east. I added a large red X at the center point between Pluto and Charon's Minimum Principle Axis of Inertia and drew a rough blue circle with a diameter of 24 degrees. This is the primary point of stress or tidal flex heat energy (bulge migration zone) induced onto Pluto by Charon and vice versa as they wobble through their long term Milankovitch cycles and short term nutations. |
As Pluto/Charon revolve through their 24 degree cycle a circular energy tidal flex footprint (bulge) is felt directly around the blue circle I've drawn on Pluto. Pluto's gravity would then collapse the stressed water ice crust at this location grinding and inducing some heat energy warming any subsurface N2. Topographically, this is where some of Pluto's lowest elevations exist. |
While we can't see whats below 30 degrees south, we can see that much of this Tenzing area (old Wright Mons) doesn't show any signs of impacts.
The material in this area is rough with 2 mile high land mass elevations but it is able to absorb impacts then back fill on short time scales (moderate heat energy). The surface of SP is obviously comparatively soft as it is primarily smooth and has zero impacts (high heat energy). To the east of SP, contained within the uplands, lakes of fluids are mingled with sharp long angular penitentes yet no impacts (moderate heat energy). |
This energy level is strong enough to make near surface crustal nitrogen convert to a liquid (explosive triple point phase) during some points in their Milankovitch cycle but it is not strong enough to cause the rocky minerals to rise to the surface (previous page) but it is probably strong enough to separate the rocky minerals from the more volatile material causing the more dense stuff to sink inward.
Volatiles are a relative term as their volatility is dependent on temperature. On Earth, water is volatile but on Pluto it is the bedrock. On Pluto volatiles are those gasses that can become gaseous like N2, CO and CH4. Water ice is not really considered volatile at Pluto temps. Some degree of differentiation is very likely created by this process but even if a fully differentiated core has developed, its a cold dead core, its too tiny to be otherwise. |
Pluto's crust is slipping over this hot spot, same as we see on Earth. The hot spot is stationary because it is caused by the gravitational interaction between Pluto and Charon as they wobble 24 degrees.
The most significant difference between Pluto's hot spot and Earth's is that tidal flex from Charon is inducing much lower energy levels at SP. This fact is demonstrated by the absence of dark surface minerals expelled by cryovolcanism. |