MadSci Network: Earth Sciences

Re: Can the earth's axis be changed by timed pinwheel explosions

Date: Thu Jan 10 22:14:58 2002
Posted By: David Smith, Faculty Geology, Environmental Science
Area of science: Earth Sciences
ID: 1009771478.Es

It is impossible for several different reasons.  Lets look at several 
aspects of this.

To begin with, it is not just the crust, which floats on the liquid core, 
but also the entire mantle.  The crust plus mantle make up more than half 
the radius of the earth.  The mantle is plastic, but it flows at a very slow 
rate (millimeters per year), to the casual observer it is "rock solid."  
Some quick calculation I did indicate that to move the crust and mantle you 
would have to supply enough force to accelerate about 40% of the total mass 
of the earth in a different direction.  That's 4 x 10^24 kg (4 million 
billion billion kilograms or 40 thousand billion megatons!) of crust and 

In addition, the earth is already rotating, so it's not just a matter of 
simple acceleration, one must take into account the substantial rotational 
inertia of that spinning mass (more math than I want to do at this hour).  
Think about how hard it is to change the axis of a spinning gyroscope.  
Furthermore, the earth has a constant feedback process that tends to keep 
the mass distribution of the earth in a constant orientation relative to the 
axis of rotation.  Since only the lithospheric plates and their mantle roots 
are non-uniform, the earth's axis tilts very slowly as the plates drift, so 
as to keep the continents as closew to the equator and as evenly distributed 
about the equator as possible.  This tendency would couteract any attempt to 
move the crust.

Then there's the issue of using nuclear explosions at all.  We can start 
with the question of whether there is enough fissionable material in the 
whole earth to provide even a tiny fraction of the number of explosions 
needed.  Even more important is the issue that what makes nuclear weapons so 
incredibly devastating as weapons makes them much less effective as 
propulsion devices.  A great deal of the mass is converted into heat and 
light.  Far more efficient propulsion is acheived by a mass cannon.  
Accelerating large masses to orbital escape speeds along something like a 
mag-lev track provides a very efficient propulsion through Newton's third 
law.  The end result, however, is that in order to move the crust and 
mantle, you'd have to throw a significant amount of it away, which 
definitely defeats the purpose.

The final issue is that the earth is a sphere and the crust is all 
interlocking, so if you could move Texas away from the equator, you would 
have to move something, like Europe, closer to it and something, like 
Australia further from it.  I'm certain the Europeans and Australians would 
not be in favor of that.  In addition, reorienting the earth's oceans would 
change the patterns of ocean currents and would have significant and 
unpredictable consequences for the climate amd food webs of the entire 

Your question seems to motivated by concern over possible effects of human 
accelerated global warming.  If so, there are many more practical solutions 
that already exist, all focused on using less fossil fuel.  Use every energy 
conserving strategy available (compact fluorescent bulbs, passive and active 
solar design, hybrid fuel vehicles, programable thermostats, etc.), ban the 
construction of new fossil fuel energy plants to force conservation,  tax 
gasoline until our prices mirror the Europeans, etc.  Sure these strategies 
cost $, but not nearly as much as an uncontrolled climate change would.

David Smith, Ph.D. (who lives above the 70 meter maximum sea level rise),
Geology, Environmental Science, and Physics
La Salle Univ., Philadelphia, PA 

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