Define tidal heating11/30/2023 The gas giants have much greater internal heating than terrestrial planets, due to their greater mass and greater compressibility making more energy available from gravitational contraction. Earth, being more massive, has a great enough ratio of mass to surface area for its internal heating to drive plate tectonics and volcanism. Mercury and Mars have no ongoing visible surface effects of internal heating because they are only 5 and 11% the mass of Earth respectively they are nearly "geologically dead" (however, see Mercury's magnetic field and Geological history of Mars). Of the terrestrial planets in the Solar System, Earth has the most internal heating because it is the largest. The internal heating within terrestrial planets powers tectonic and volcanic activities. Thus, Earth's Moon, which has no alternative source of internal heating is now geologically dead, whereas a moon as small as Enceladus that has sufficient tidal heating (or at least had it recently) and some remaining radioactive heating, is able to maintain an active and directly detectable cryovolcanism. After these radioactive isotopes had decayed to insignificant levels, the heat generated by longer-lived radioactive isotopes (such as potassium-40, thorium-232, and uranium-235 and uranium-238) was insufficient to keep these bodies molten unless they had an alternative source of internal heating, such as tidal heating. In the early history of the Solar System, radioactive isotopes having a half-life on the order of a few million years (such as aluminium-26 and iron-60) were sufficiently abundant to produce enough heat to cause internal melting of some moons and even some asteroids, such as Vesta noted above. The internal heating keeps celestial objects warm and active. The amount of internal heating depends on mass the more massive the object, the more internal heat it has also, for a given density, the more massive the object, the greater the ratio of mass to surface area, and thus the greater the retention of internal heat. Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, resulting from contraction caused by gravity (the Kelvin–Helmholtz mechanism), nuclear fusion, tidal heating, core solidification ( heat of fusion released as molten core material solidifies), and radioactive decay. JSTOR ( February 2012) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. What prompted that comment that the TRAPPIST-1 planets may be subject to tidal heating is that some of those planets appear to be in an orbital resonance, with periods being very close to small integer multiples of one another.This article does not cite any sources. This makes for a rather nice hysteresis loop. Tidal stresses eventually come into play again, warming up Io and decrasing its tidal quality factor. The competing forces from Europa and Ganymede can then make Io's orbit more eccentric. This makes it less susceptible to further circularization. Io cools down, resulting in an increase in its tidal qualify factor Q. The tidal stresses become less severe as Io's orbit becomes closer to circular. Those tidal stresses by Jupiter in turn act to circularize Io's orbit. The elliptical nature of Io's orbit results in time-varying tidal stresses on Io, which makes Io geologically active. One of the consequences of these resonances is that Europa and Ganymede act to pull Io's orbit out-of-round i.e., more elliptical. Io's orbit is not circular, thanks to those orbital resonances. Io would not exhibit any tidal heating if its orbit was circular. The three innermost of the Galilean moons of Jupiter, Io, Europa, and Ganymede, are in a 4:2:1 orbital resonance. What drove the comment that "the tidal forces between the planets are not negligible" was the Jovian moons. The tidal force of 1c on 1b is defined as the differential force of gravity across 1b, that is, the difference of the force of gravity on the side of 1b facing towards 1c and the force of gravity on the side of 1b facing away from 1c. See the figure below which describes the parameters. I'm going to calculate the tidal effects of TRAPPIST-1c on TRAPPIST-1b (simply because, a priori, this seems likely to be where the strongest tidal heating will be induced). Calculating tidal forces from TRAPPIST-1c on TRAPPIST-1b But let's try a few back of the envelope calculations to see what we get. This is a complicated question that would really require a full physics simulation and better knowledge of the system to accurately answer.
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