HR: 0800h
AN: P51B-0928    [Abstracts]
TI: What can the Super-Rotation of Earth's Inner Core Tell us About the Disappearance of Oceans on Mars?
AU: * Singer, S F
EM: singer@sepp.org
AF: Univ of Virginia, 1600 S. Eads St., #712-S, Arlington, VA 22202 United States
AB: Zhang et al (Science 309, p.1357, 26 Aug. 2005; see also news story by Richard Kerr) have confirmed that the Earth's inner core is spinning faster than its outer layers. [Earth has a solid inner core whose radius is about 1,200km and a fluid outer core with 3,500km radius. The core plays an important role in the dynamo that generates Earth's magnetic field.] The researchers compared seismic waves produced by pairs of earthquakes occurring at the same location on the planet, but at different times. Waves from these nearly identical quakes passed through the Earth's core. The results show that the inner core is rotating faster than the rest of the planet by about 0.04 seconds per year. We now develop a chain of speculative hypotheses, as follows: 1. We posit that the super-rotation of the inner core is driven by lunar tidal forces and depends on the differences (between inner and outer core) in distance from Earth center and in elastic constants - and therefore their different dissipation rates of rotational kinetic energy. [We note that this difference in rotation rate -- and therefore also the geomagnetic field - were much greater when the Moon was closer to Earth some billions of years ago. Such a stronger field also would have provided a better shield against high-energy cosmic rays and led to a lower atmospheric albedo.] 2. To support the idea that the Moon drives the geomagnetic field, we note that Venus, which has no moon, has no appreciable magnetic field. What about Mars? 3. The present Martian moons Phobos and Deimos are much too small to have much effect on Mars rotation or its core. But if we accept that they are the remnants of a very much larger body, captured by Mars shortly after its creation [1], then we have a mechanism for producing differential rotation within Mars and create a magnetic field. 4. But this Mars-Moon disappeared - except for small remnants - within a short time by spiraling into Mars because of tidal friction, thus removing the driving force for Mars magnetic field, which slowly decayed away. Evidence for such a paleo-field has been reported. 5. Once the Martian field had decayed, Mars lost its protective magnetosphere. This now permitted the solar wind to sweep away hydrogen and oxygen ions - thus greatly enhancing their escape rate beyond that for a neutral exosphere. In this manner, water on the surface would be quickly removed -- as water vapor was dissociated and ionized by solar UV radiation. This process may explain why Mars oceans disappeared while subsurface water was preserved. 1. Singer, S. F. (2003), Origin of Phobos and Deimos: A new capture model, paper presented at the Sixth International Conference on Mars, Calif. Inst. of Technol., Pasadena, 20-25 July.
DE: 0328 Exosphere
DE: 1239 Earth rotation variations
DE: 1595 Planetary magnetism: all frequencies and wavelengths
DE: 5749 Origin and evolution
DE: 6230 Martian satellites
SC: Planetary Sciences [P]
MN: Fall Meeting 2005