The New York Times recently (June 21, 2018) speculated about a Summer Solstice mystery: "Does the Earth's Tilt [of its spin axis, currently 23.5 degrees] Hold the Secret to Life?"  It encouraged me to write about a different kind of speculation, linking the super-rotation of the Earth's core to the possibility of life on Mars.

It should be understood that the chain of events described below involves much uncertainty.  Nevertheless, each link in the chain seems plausible – even if I cannot describe it quantitatively.  So here goes:

1. Super-rotation of the core

Seismic data, taken over a period of several years (Zhang, et al., Science 2005), suggest that the (innermost, solid iron) core is rotating slightly faster than the rest of the Earth, at 0.3-0.5 degrees/yr.  We don't know if this super-rotation is constant or varies over time.  The analysts did not suggest a cause, hence relatively little attention has been devoted to the phenomenon.  Most scientists I talked to had never heard of it.

2. Possible explanation of super-rotation

If I invert the question and ask, "Why is the Earth rotating slower than its core?," then the answer becomes clear to me, and I can even calculate and estimate its magnitude.  The slowing down may be caused by tidal friction, produced by the Moon.  This also means that the super-rotation has been going on for billions of years.

3. Production of Earth's magnetic field

We may assume that the differential rotation at the inner-core boundary with the (still liquid) outer core "winds up" the magnetic lines of force and thus produces and strengthens the geomagnetic field.  I have calculated that the geomagnetic field has a decay time of only about 20,000 years, based on the likely conductivity of the iron core.  Clearly, some kind of energy source is required to maintain the magnetic field.  I suggest that the source is kinetic energy of rotation.

(The time variation and reversal of the geomagnetic field has been worked out by Richards and Glatzmyer on the basis of magneto-hydrodynamic circulation within the liquid part of the core.  The inner core is solid and is thought to be growing in size.  An idea of their relative dimension may be gained from Figure 1.)

Figure 1.

4. The geomagnetic field establishes the magnetosphere

This is the standard explanation for the existence of the magnetosphere, the outermost layer of the Earth's atmosphere, consisting mostly of ions of atomic hydrogen, protons, magnetically trapped and spiraling around the lines of force, produced as the Earth neutral exosphere is dissociated and ionized by solar UV radiation.

The magnetosphere extends from ~300 km to about 10 Earth radii (Earth's radius is ~6,400 km, 4,000 miles) and is really an extension of the Earth's ionosphere, which occupies the region of ~80-300 km.

5. The magnetosphere shields the Earth's lower atmosphere from the direct impact of the "solar wind," consisting mainly of high-speed protons and some heavier nuclei.  The solar wind would help to ionize the atmosphere and also "sweep away" the outer portions – thus speeding up the "escape" of this outermost atmosphere, the exosphere, as it is labeled, where the density is so low that the mean free path between collisions becomes long enough that one can ignore collisions.  The concept of temperature loses significance.

6. We may assume that similar processes happened on Mars.  I believe that its core was liquefied by tidal friction, but it has cooled and is no longer liquid.  Mars no longer has a general magnetic field like the Earth.  Its magnetosphere has now disappeared, but its shielding effect may have lasted long enough, I believe, to maintain an ocean on Mars's surface for some time.

7. Lundin and others have measured the removal of the Martian upper atmosphere by the sweeping action of the solar wind.  The crucial question is this: did the Mars atmosphere and surface ocean exist long enough to permit the creation of life forms – as it did on Earth?

I can calculate a "survival time" for the ocean using available physical theory.  However, this calculation is complicated by the greenhouse effect and possible freezing over of the ocean surface, which would stop its evaporation.  In addition, covering up the ocean, or the remaining puddles of water, affects survival.  But I don't know how long it takes for living forms to come into being; I assume that this interval is fairly short.

8. We can calculate all we want, but the answer will be available eventually if we discover life forms, either krypto-life or paleo-life, just below the Martian surface.

Life may have been produced several times during the early history of Mars but then wiped out by solar UV radiation or solar wind, or by the ionization produced by cosmic rays – unless protected by a magnetic  field – as on Earth – or by a protective covering of dust or soil.  That is to say life may exist only below the Martian surface.

Conclusion

There are many links in this chain of events, many of them quite speculative and hard for me to quantify.  But the sequence of events seems plausible.  I summarize the main positive results:

1. An explanation of the observed super-rotation in terms of tidal friction, produced by a (captured) moon.  The Mars moon has now disappeared, leaving behind two fragments, Phobos and Deimos.  

2. A theoretical construct that accounts for the maintenance of the geomagnetic field, with kinetic energy of Earth's rotation as the energy source.

3. A conceptual calculation of the survival time of an ocean on Earth, with the protection of the magnetosphere – and on Mars, where the magnetosphere survives only as long as the Mars moon and a general magnetic field exist.