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The Centers of PlanetsBack in 1935, Eugene Wigner, one of the founding fathers of quantum mechanics and at the time a professor at Princeton University, suggested that hydrogen, an inert molecular gas at ambient conditions, could turn into a metallic solid, similar to lithium or sodium, at sufficiently high pressure. Wigner's proposal implied a remarkable complexity for "element one," the simplest chemical entity, one electron bound to one proton... Jupiter's magnetic field, first measured by Voyager spacecraft, is ten times stronger than Earth's, and its pattern is considerably more complex. Part of this complexity could be accounted for if the source of the field lay much farther from the center, in relative terms, than does Earth's. Wigner's prediction of metallic hydrogen was based on a simplified analysis of the electronic ground state, but the pressure he calculated for the transition to the metallic state, about 250,000 atmospheres, corresponded to a depth of less than one-twentieth of the planetary radius of Jupiter. In other words, most of the solar system's largest gas giant had to be in a metallic state -- although the metallic hydrogen would have to be a fluid rather than a solid to provide dynamo action... The fact is that the Earth's core is not pure iron but contains about 10 percent (by weight) of other constituents. If you compare the density of the outer core that is derived from seismological data with that of pure iron shocked to comparable pressures and temperatures, the core's density turns out to be about 10 percent lower. Even when the melting temperature of pure iron is accurately known at 2 million to 4 million atmospheres of pressure, we will still have to make a correction for the effect of contaminants. Alloying often decreases the freezing temperature of a material; this is why ice can be melted by putting salt on top of it. The actual freezing temperature at the innerouter core boundary may therefore be 1,000 kelvins or so lower than that of pure iron.
by Sandro Scandolo
and Raymond Jeanloz
U of M researcher simulate characteristics of planetary coresThe researchers calculated what would happen at temperatures and pressures likely near the cores of the two exoplanets, Jupiter and Saturn, where temperatures run close to 18,000 F and pressures 10 million bars (a bar is essentially atmospheric pressure at sea level). They found that even post-perovskite could not withstand such conditions, and its crystals would dissociate into two new forms. Focusing on one of those crystals, the researchers discovered that they would behave almost like metals. That is, electrons in the crystals would be very mobile and carry electric current. This would have the effect of supporting the planet's magnetic field (if it has one) and inhibiting reversals of the field. The increased electrical activity would also help transport energy out of the core and toward the planet surface. This could result in more severe activities such as quakes and volcanoes on the surface. The effect would be much stronger in Dense-Saturn than in Super-Earth.
posted on 04/02/2006 2:46:30 PM PDT
Scientific maverick's theory on Earth's core up for a test[Herndon] draws unhappy conclusions from his bumpy scientific career. Had his two sons -- now physicians -- planned to become scientists, he says, "I would have steered them away from it because you can't make a living and do legitimate science; you have to 'howl with the wolves' or you don't survive. This is a sad testament to our times. There's something very wrong in American science."
by Keay Davidson
Monday, November 29, 2004
posted on 04/02/2006 2:47:56 PM PDT
posted on 04/02/2006 2:50:53 PM PDT
(Darwinian logic -- It is just-so if it is just-so)
Getting to the problem of the core[T]he core cannot be made from iron alone because its density, determined by measuring the speed of seismic waves - is too low. This means there must be lighter elements there that are lowering its density. What is more, they have to be elements that are common in our solar system... "When you're talking about possible impurities in the Earth's core, the most likely things are the most common things like silicon, sulphur and oxygen".
Earths core chemistry is silicon enhancedA team of scientists led by Jung-Fu Lin, a doctoral student in geophysical sciences at the University of Chicago, has found experimental evidence suggesting that the Earth's inner core largely consists of two exotic forms of iron instead of only one. These exotic forms of iron now appear to be alloyed with silicon. A previous study had once practically eliminated silicon as a candidate lighter element of the inner core... Seismologists have made further deductions about the characteristics of Earth's core from the way that seismic waves travel through Earth from earthquakes and explosives. "They noticed that there has to be about 10 weight percent of a lighter element in the outer core and anywhere from zero to 4 weight percent of a lighter element in the inner core" Heinz explained.
Hydrogen In The Core:Once a magma ocean was formed due to the blanketing effect of an impact-induced steam atmosphere of hundreds of bars, it absorbs most of H2O in the accreting planetesimals. Then the hydrogen is partitioned between the silicate melt and the molten iron that is sinking through the magma ocean to form the core. Thus, hydrogen is partitioned between the atmosphere, magma ocean and core... Two types of the protoatmospheres were proposed to produce the magma ocean: the primary atmosphere consists of the solar nebula gas, and the secondary atmosphere consists of the impact-degassed volatile... atmospheric hydrogen was oxidized by FeO in the magma ocean at its surface, transported through the magma ocean as H2O, and reduced by metallic iron in the deeper part of the magma ocean to form the iron-hydrogen alloy... On the other hand, if the magma ocean was formed through the blanketing effect of the impact-induced steam atmosphere, the hydrogen incorporation into molten iron may have decreased the mass and optical thickness of the atmosphere, and weakened the blanketing effect, because there was no nebula gas that supplies hydrogen to the atmosphere.
An Evidence For The State Of Lost Protoatmosphere
T. Okuchi, Y. Abe and H. Iwamori
Wobbles within wobblesA new theory proposes that iron-rich sediments are floating to the top of the Earth's core and sticking like gum to the bottom of the mantle, creating drag that throws the Earth's wobble off by a millimetre or two over a period of about 18.6 years... As the Earth spins on its axis the moon and sun tug on its bulging equator and create a large wobble or precession, producing the precession of the equinoxes with a period of 25,800 years. Other periodic processes in the solar system nudge the Earth, too, creating small wobbles - called nutations - in the wobble. The principal components of the nutation are caused by the Earth's annual circuit of the sun and the 18.6-year precession of the moon's orbit... An annual deviation that lagged behind the tidal pull of the sun first suggested to Buffett 10 years ago that strange processes may be going on at the boundary between the mantle, made up of viscous rock that extends 1,800 miles below the crust, and the outer core, which is thought to be liquid iron with the consistency of water. The inner core, made of very pure, solid iron, rotates along with the outer core, dragging the Earth's magnetic field with them... Because the Earth's core rotates about a slightly different axis than the mantle (due to the tug of the Sun and Moon), the core's magnetic field is dragged through the mantle, passing unhindered because the mantle does not conduct electricity. The porous, iron-containing sediment stuck to the mantle, however, would resist the rotation of the magnetic field, creating just enough tug to perturb the Earth's rotation.
probe planet's core
posted on 04/04/2006 11:24:18 PM PDT
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