EFFECTS OF TIDAL HEATING ON HABITABILITY
The search for life and environment suitable to breed life beyond earth has been of key interest to scientists. Heat is important in the ability of a planet to support life as we know it. Apart from the direct rise or fall in temperature of a planet due to its proximity to its host star, tidal heating could either be too great or insufficient to allow habitability. Tidal heating has provided another way to limit a planet's habitability other than the amount of energy it receives directly from the sun/host star. A prerequisite for habitability of a planet or moon is it's ability to support liquid water (as found in the subsurface oceans of Europa and Enceladus). Bodies too close to their host stars, or in the case of moons, host planets, have tidal forces that are too high hence, temperatures that cause the planet to be overly active, for example, Io. Others maybe too far and consequently geologically inactive i.e frozen (e.g Dione). Other factors such as the shape (eccentricity) of the orbit also come into play.
Most extrasolar planets have been found to orbit around their host stars in elliptical orbits unlike the circular orbit of our solar system. This has great implications on the generation of tidal heat as explained earlier. Tidal heating on these extrasolar planets may be sufficiently large to drive plate tectonics and other geophysical processes much like that of earth's. However, it will most likely be too extensive to support life(8) and will give rise to high levels of volcanism and stripping of water from the atmosphere as in the case of Io. This greatly diminishes the habitability of these planets. An example of this is that of the innermost planet in the HD 40307 system where the tidal heat exceeds that of Io[10]. Planets that have lost their water due to tidal effects such as the aforementioned are referred to as Tidal Venus.
An effect of substantial tidal heating is the outgassing of volatiles which replenish the atmosphere. On Europa and Enceladus, heat generated due to tidal forces has been suitable to create subsurface oceans. Tidal heating, solely or in conjuction with radioactive decay, fosters plate tectonics which pulls excess carbon, a greenhouse gas, from the atmosphere of the orbiting body and is involved in the generation of a magnetic field[11]. A magnetic field is important because, as in the case of earth, it protects the planet from solar winds or radiation from the host planet. The severe greenhouse effect on Venus is most likely caused by the lack of plate tectonics.
Most extrasolar planets have been found to orbit around their host stars in elliptical orbits unlike the circular orbit of our solar system. This has great implications on the generation of tidal heat as explained earlier. Tidal heating on these extrasolar planets may be sufficiently large to drive plate tectonics and other geophysical processes much like that of earth's. However, it will most likely be too extensive to support life(8) and will give rise to high levels of volcanism and stripping of water from the atmosphere as in the case of Io. This greatly diminishes the habitability of these planets. An example of this is that of the innermost planet in the HD 40307 system where the tidal heat exceeds that of Io[10]. Planets that have lost their water due to tidal effects such as the aforementioned are referred to as Tidal Venus.
An effect of substantial tidal heating is the outgassing of volatiles which replenish the atmosphere. On Europa and Enceladus, heat generated due to tidal forces has been suitable to create subsurface oceans. Tidal heating, solely or in conjuction with radioactive decay, fosters plate tectonics which pulls excess carbon, a greenhouse gas, from the atmosphere of the orbiting body and is involved in the generation of a magnetic field[11]. A magnetic field is important because, as in the case of earth, it protects the planet from solar winds or radiation from the host planet. The severe greenhouse effect on Venus is most likely caused by the lack of plate tectonics.