A Look At Earth's Dipole Magnetic Field And The Problem Posed For "Young Earth" Creationists

 

How the Earth's magnetosphere protects our planet from the onslaught of the solar wind. But to have a protective magnetosphere, there must be an adequate magnetic field to sustain it. 

Our planet's dipole field is extremely critical in terms of maintaining its residual magnetic field of roughly 3.1 Gs (gauss) which in turn implies the capacity to provide a magnetosphere that's capable of intercepting the high energy particles of the solar wind as well as other solar-flare triggered particles. The attached diagram shows the response (generic) of our magnetosphere to the onslaught of the solar wind.

The fast solar wind can attain speeds in excess of 500 km/s and emerges from coronal holes. These latter comprise dark holes visible in coronal imagery indicating where the Sun's magnetic field lines open up and extend into space thereby providing an escape channel for hot solar plasma. In the coronal image below these holes, as well as magnetic field arches, can clearly be seen:

This fast solar wind  is differentiated from the much slower moving stream of solar wind that floods the solar system continuously, and defines the "slow wind". It defines what we call the heliosphere which is essentially the solar wind's" bubble of influence.

The heliosheath occurs at the far edge of the heliosphere. More technically, it occurs between the "termination shock" and the "heliopause".   (For reference, the heliosheath occurs at the far edge of the heliosphere. More technically, it occurs between the "termination shock" and the "heliopause".    The heliopause  is the interface where the solar wind is stopped by the interstellar medium. )

A  key parameter for defining the dipole field's extent is the pitch angle:

sin (q ) > Ö (B_min / B _max )

Designating the thresholds for when confined particles will be reflected within the  flux tube, i.e. "mirrored" via an in situ "magnetic mirror" sustained by the Earth's magnetic field.

In other words, if the Earth's field were to go to zero, then the magnetosphere and its protection would be lost. The magnetosphere is only in place because the Earth generates a magnetic field which then enables a magnetosphere to form.

Typically, the magnetosphere will diminish during a field reversal and even B(E)   ->  0, in particular because such reversals include an interval wherein no magnetic field exists. This zero field condition may last from 100 to 1000 years, perhaps more. In such a case, the magnetic field -which normally acts as a protective barrier to the flux of energized particles known as the solar wind- ceases to do that. This means that in the event of major solar flares, the particle flux might attain levels that can be lethal to some life forms.

The problem posed by the solar wind's (or flare) energetic particles is to expose many life forms to much higher radiation levels. To give an indication of the magnitude, when a medium intensity (not even terribly large) solar wind normally "blows" along the magnetosphere boundary an effective MHD (magneto-hydrodynamic) generator is produced. All such "generators" are defined by virtue of the free electrons and protons in the solar wind cutting across the Earth's resident magnetic field.

With an induced voltage of this generator up to 150 kV (150,000 V) a total power of more than 1 million megawatts is produced. That is 1 million joules of energy per second. Entering the Earth's atmosphere unabated such energy flux would pose major issues for any organisms, including humans.

Now, let's look at the dipole field proper, in as much as it gives rise to the magnetosphere. First, the poles of the dipole are not coincident with the geographic north or south poles, which are defined at latitudes 90 deg N, and 90 deg S, respectively. One positional computation put them at 79 deg N, 70W, and 79 deg S, 70 E, respectively.

The magnetic flux density defined for the Earth is given as (Hargreaves, The Solar-Terrestrial Environment, Cambridge University Press, p. 150):

B(r,L) = M/r ³  [ 1 + 3 sin 2 L] ^1/2 

where M is the dipole moment (M ~ 10 ^25.9  G cm ³ , with G in gauss), r the geocentric radial distance and L the magnetic latitude (e.g. 70 deg for the locations given earlier).

Generically, the vector magnetic field at vector position x due to a magnetic dipole of vector dipole moment m at the origin, is given by:

B = {3(m*x)x - x }2/ ‖ x‖ ³ 

Meanwhile, the field components in the r and L directions are respectively (Hargreaves, ibid.)

B(r) = - 2M sin(L) / r³ 

B(L) = M cos (L) / r³ 

The characteristic time for variation of the Earth's magnetic field is given by:

dB/dt = B(r,L)/t

The magnetic moment  m (m) is a constant of the motion: viz

 m (m) = m(v⊥) 2 / 2B= const.

Bear in mind the gyration energy: E(g) =  m(m)B = m/ 2 (E/B) 2

Young Earth creationists argue that if the Earth's dipole changes by 5% per century, the Earth can't be much older than 20 centuries[1] (i.e.. 20 cen x 5%/c = 100 %) However, simple computations using the preceding easily refute that contention. In fact, one can use test particles, say electrons, of specific energy (say 1 keV) in the magnetosphere, as a basis to do the differentiation of B(r,L) taking into account the constants of the motion, especially m(m) and showing this is preposterous. For one thing, the variables B(r), B(L) are likely to vary and not be uniform relative to each other, so "5% per century" as a defined uniform scale variation for B(r, L) is nonsense. Worse, the remanenece factor is not taken into account, and from even basic computations of this type one can show a minimum time scale of at least 250,000- 300,000 YEARS for field reversal (for the field components B(L) and B(r) to attain magnitudes that yield a discernible magnetic moment, M.

Even the lowest estimates for such computation, say for those associated with dB(r,L)/dt (via integration) yield ~100,000 yrs. and thus more than fifty times larger than what the Young Earthers claim.  Again,  all this discloses a sect that is more invested in using confirmation bias and supernaturalist bunkum to peddle their pseudo-science, than to confront the facts.  Much like the global warming/ climate change deniers.