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Author | Topic: Mercury's Magnetic Field | |||||||||||||||||||||||
PaulK Member Posts: 17828 Joined: Member Rating: 2.5 |
Water isn't known as being useful in permanent magnets. And I very much doubt that 2 Peter 3:5 is intended to suggest that the planet Earth was formed by transmuting water.
Quite frankly it looks to me like just another creationist twisting the Bible to try to support their beliefs.
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jar Member (Idle past 425 days) Posts: 34026 From: Texas!! Joined: |
What's the density of Mercury, the planet?
How does that density relate to the density of other planets? Aslan is not a Tame Lion
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Sorry, but Humphreys seems to be a bit of a Kook.
at the instant God created the water molecules, the spins of the hydrogen nuclei were all pointing in a particular direction. By the ordinary laws of physics, the spins of the nuclei would lose their alignment within seconds, but the large magnetic field would preserve itself by causing an electric current to circulate in the interior of each planet. By the same laws, the currents and fields would preserve themselves with only minor losses, as God rapidly transformed the water into other materials. After that, the currents and fields would decay due to electrical resistance. He supplies no evidence for any of this. He essentially says in this article, "I said this back in 1984 and you'll just have to believe me on it." He provides no model parameters. This is "Goddidit" in its purest form. Also, Humphreys doesn't address magnetic field reversals which have been observed on Earth: Geomagnetic reversal - Wikipedia How is this reconcilable with Humphrey's model? How could the Earth's magnetic field flip 1,000-10,000 if the Earth is only 6,000 years old? If it isn't that's a huge problem with his model. Mercury's magnetic field is well in line with its density (almost the same as the Earth) which implies that it has a significant metal core. When a (partially molten) metal core rotates, it generates a magnetic field. This is not the same as the magnets you have on your refridgerator.
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Since I have my space science book on hand:
Planet- Density (kg/m3) Mercury- 5430 Venus- 5240 Earth- 5515 Mars- 3940 (Comins and Kaufmann, Discovering the Universe, 2005, Freeman press)
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jar Member (Idle past 425 days) Posts: 34026 From: Texas!! Joined: |
How's about gas Giants. Jupiter and Saturn have a magnetic field?
Aslan is not a Tame Lion
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Yup, both gas giants have a magnetic field, and pretty strong ones at that. It's largely due to the huge volume of metallic hydrogen deep beneath their surfaces. Metallic hydrogen is an interesting consequence of hydrodynamic equilibrium at the pressures found deep in these planets- essentially the pressure is so great that hydrogen's electron clouds are shared, just like they are in a metal. And since both planets are strongly rotating, that produces the large magnetic field of both planets.
Oh! The densities of the gas giants-Jupiter- 1330 Saturn- 700 Uranus- 1300 Neptune- 1760 This message has been edited by Matt P, 10-03-2005 06:04 PM
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jar Member (Idle past 425 days) Posts: 34026 From: Texas!! Joined: |
so density is only a factor in relation to what is required to create something metallic?
Aslan is not a Tame Lion
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Correct. Density is important when constrained by composition. The gas giants have metallic fields because they are so massive that the pressure is high enough to force electron cloud sharing of things that ordinarily wouldn't share electrons (H, He, CH4, H2O).
However, the rocky planets have significant metal cores which encourages a magnetic field. Mars doesn't have much of a magnetic field since its density is so low- its core must not be completely metal, or really small. The final factor is rotation- Venus rotates very slowly, so it has a very weak magnetic field, and the same is true of Mercury.
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jar Member (Idle past 425 days) Posts: 34026 From: Texas!! Joined: |
Okay.
What about the Giants. Not super-giants like Jupiter and Saturn but Uranus and Neptune? Aslan is not a Tame Lion
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PaulK Member Posts: 17828 Joined: Member Rating: 2.5 |
Looking at the comparisonshere Humphreys figures appear to be a bit off.
Humphreys gives a figure for the moon that is more than 10,000,000 times less than that for Earth. Yet on the site referenced above t he moon's magnetic field is listed as being only 109 times weaker.[Added in edit - it MIGHT be a typo for 10^9 - but that would still disagree with Humphreys] The estimates Humphreys gives for Uranus and Neptune are listed as maximum values. Both are larger than the value for Saturn, so it seems that they cannot be "right on" (in fact they are more than 10x the actual figures). It seems likely that his "success" is due solely to making vaguer predictions that were inherently less risky. Worse, Humphreys relies on Barnes discredited claims about the Earth's magnetic field. See here for more informationat This message has been edited by PaulK, 10-04-2005 03:13 AM
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gene90 Member (Idle past 3854 days) Posts: 1610 Joined: |
[Quoting Matt P]
quote: I would ask how, if the Earth's field were produced by a permanent magnet rather than by a dynamo, why it flips.
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Frankly I'm not familiar with the origin of the giant planet's magnetic fields. I think the info is sketchy, since we've only looked at it from Voyager 2. Looking it up shows way too much magnetohydrodynamics for my taste. However, the general theme is that the means through which these fields are generated are fundamentally different.
Here are a few references:
INTRINSIC MAGNETIC-FIELDS OF THE PLANETS - MERCURY TO NEPTUNE NESS NF PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 349 (1690): 249-260 NOV 15 1994 Abstract: In the past three decades, studies of the magnetic fields of Earth's Moon and all the planets, except for Pluto, have been conducted by spacecraft of the U.S.A. and of Venus and Mars by the former U.S.S.R. Among the terrestrial planets, only Mercury (Mariner 10: 1974 and 1975) is globally magnetized while the Moon and Venus are unmagnetized. The situation at Mars is still unclear, but if any global field exists, it is quite small. In 1979, Pioneer 11 discovered a magnetic field and radiation belt at Saturn, further elaborated on by Voyagers 1 (1980) and 2 (1981). Pioneers 10 (1974) and 11 (1975) and Voyagers 1 (1979) and 2 (1979) examined in detail the magnetic field of Jupiter, which had been inferred initially and studied remotely due to its non-thermal radio emissions in the late 1950s. Jupiter's magnetic field is much stronger than Earth's and distinctly nondipolar close to the planet. Saturn has a much weaker field than Jupiter, and it is surprisingly axisymmetric (to degree n = 3) with respect to its rotation axis. The Voyager fly-bys of Uranus and Neptune in 1986 and 1989 discovered global magnetic fields and trapped energetic particle radiation belts. Both Uranus and Neptune display remarkably similar magnetic fields (quite different from Jupiter, Saturn and Earth). In an astrophysical sense, Uranus and Neptune are described as oblique rotators because of the large angular offset of their magnetic axes from their rotation axes (59 degrees and 47 degrees). Additionally, their magnetic 'centres' are displaced by substantial fractions of a planetary radius (0.31 R(U) and 0.55 R(N)) This paper summarizes our present knowledge of the quantitative characteristics of the magnetic fields of these planets.
MAGNETIC-FIELDS OF THE OUTER PLANETS CONNERNEY JEP JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 98 (E10): 18659-18679 OCT 25 1993Abstract: It is difficult to imagine a group of planetary dynamos more diverse than those visited by the Pioneer and Voyager spacecraft. The magnetic field of Jupiter is large in magnitude and has a dipole axis within 10-degrees of its rotation axis, comfortably consistent with the paleomagnetic history of the geodynamo. Saturn's remarkable (zonal harmonic) magnetic field has an axis of symmetry that is indistinguishable from its rotation axis (<< 1-degrees angular separation); it is also highly antisymmetric with respect to the equator plane, According to one hypothesis, the spin symmetry may arise from the differential rotation of an electrically conducting and stably stratified layer above the dynamo. The magnetic fields of Uranus and Neptune are very much alike, and equally unlike those of the other known magnetized planets. These two planets are characterized by a large dipole tilts (59-degrees and 47-degrees, respectively) and quadrupole moments (Schmidt-normalized quadrupole/dipole ratio almost-equal-to 1.0). These properties may be characteristic of dynamo generation in the relatively poorly conducting ''ice'' interiors of Uranus and Neptune. Characteristics of these planetary magnetic fields are illustrated using contour maps of the field on the planet's surface and discussed in the context of planetary interiors and dynamo generation. Sorry to say, but ugh. It's easy to see how a charlatan can slip into this field.
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Good point. I don't think it is able to flip in Humphrey's model.
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Coragyps Member (Idle past 765 days) Posts: 5553 From: Snyder, Texas, USA Joined: |
Mars doesn't have much of a magnetic field since its density is so low- its core must not be completely metal, or really small.
But Mars does have some crustal magnetism - leftovers from minerals getting magnetized a few billion years ago, when it still had a molten core. CF, how fast can a Mars-sized body's core cool?
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Matt P Member (Idle past 4805 days) Posts: 106 From: Tampa FL Joined: |
Let's see. The (simplified) diffusion equation is:
dT/dt = k d^2 T / dz^2 where T is temperature, t is time, and z is the size of the body (not spherical, but it's a good guess). k is the diffusivity, and for a rock/metal mixture, one might expect it to be on the order of 10^-3 to 10^-4 with SI units. Rock alone is 10^-6, but metal is much more conductive. So to an order of magnitude: t = z^2 / k With the Martian radius as 3380 km, this would give a lifetime of about 1e9 years. Naturally this is an oversimplification- I've excluded radioactivity, temperature dependence of k, and I've also excluded accretional heating. But it's in line with what we might expect from the remnant magnetism.
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