Volcanic activity on Mars appears to have continued into the present and the discovery of slope wash and alluvian deposition, possibly deposited within last 5 years, indicate an even more active Mars. Io is now considered the “most geologically active body in the solar system” New Horizons photographed a 200-mile-high plume from Io’s volcano Tvashtar glowing lava and gas pockets. Tidal heating in some form may well be active in Mercury, Venus, Earth, Mars, Galilean satellites, and Saturn’s moons. Tidal heat is manifested in volcanic activity and surface melting, generally resulting in resurfacing of planetary bodies affected by tidal stresses. Other bodies have since been found to be impacted by tidal heating as well, most recently Saturn’s moons, Enceladus and Dione, which have both shown evidence of geysers. Thus, Voyager “proved” tidal heating is an effective energy-transfer system. The heating cycle then begins again with heat building until there is another eruptive phase the process eventually results in the resurfacing of Io with layer upon layer of flood basalts. This loss of internal heat cools Io, making it less responsive to Jupiter’s tidal pull, thus reducing the effectiveness of tidal heating. Io’s episodic heating cycle results in massive heat loss in the eruptive phase, as heat is dumped onto the surface through basaltic outpourings. We’ve learned that gravitational stresses produced by Jupiter cause the heating of Io and Io is now recognized as the “most” active planetary body in the solar system. The Voyager flyby in 1979 of Io, Jupiter’s innermost moon, introduced a revised concept of tidal heating. Post-Apollo exploration of the solar system has made us aware that tidal heating caused by the gravitational pulling and tugging between two planetary bodies is very much a factor in planetary resurfacing. In general, no evidence of a secondary heat source such as tidal heating was known and theoretical modeling of tidal heating didn’t seem to find it a significant contributor to overall planetary heating. Earth was assumed to still have its heat of accretion only because of its relatively large size. The earth was thought unique being the only “active” planet in the solar system with its plate tectonics, volcanic resurfacing, and biological life. Earth’s moon and Mars were both thought to be small planetary bodies which had lost all of this primordial heat and thus were considered cold “dead” bodies. This initial heat, it was thought, would be gradually lost over time. Tidal heating (also known as tidal flexing) occurs through this tidal friction.ĭuring the Apollo age it was assumed by scientists that planetary bodies contain primarily the heat of their formation (accretion) and some residual isotopic decay. The orbital energy generates internal friction, which heats its interior. Orbital energy that is dissipated as heat in either the surface ocean or interior of a planet is known as tidal heating.
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