[greensleeves (OP)]

Although similar in size and mass, Venus differs from Earth in that it has a very much weaker magnetic field.

As I understand it (please correct me) a magnetosphere can be generated by both conduction and convection processes, but conductivity should be similar on both planets as both are believed to have a similarly sized iron core.

That leaves convection, which requires some degree of fluidity, and a process which generates movement of electrical charges within that fluid. There seem to be several possible processes involved in creating convection currents on Earth which may not be in effect on Venus;

1) Planetary rotation, which is much slower on Venus than Earth. How significant is this in the generation of the magnetosphere on Earth?
 
2) Earth has a very sizeable and influential moon, whilst Venus does not. Does Earth's moon generate tidal convection currents at any level within the planet's interior which may assist in the formation of a magnetosphere (and as a side issue, also the generation of plate tectonics on Earth - another difference between the two planets)

3) Heat flux throughout the planet's interior. Although there must be a gradation in temperature between the immensely hot core and the surface on both planets, on Venus there is believed to be a much smaller temperature difference between the surface crust and the mantle, due to the high surface temperatures on the planet. Can magnetosphere-inducing convection currents be generated by heat flux at any level within the planet's interior including the upper mantle, or just in the core?

4) Solidification in the core. As I understand it, Earth's core is differentiated into a solid inner core and a molten outer core, and convection currents generated at this junction as iron solidifies on to the inner core, is believed to be the primary cause of Earth's continuously replenished magnetosphere. Why should this be so? And why should Venus lack this process? Is Venus's core entirely solid, or entirely molten? Or is there some other reason why convection currents are not being generated at Venus's core, in the same way as they are on earth?

I would be grateful for any corrections to these suppositions, or explanations as to the causes of the discrepancy between Earth's strong magnetic field and Venus's very weak magnetic field.

[syhprum]

I am surprised at the lack of interest in this question here is an excellent article that discusses the matter.




http://dawn.ucla.edu/personnel/russell/papers/venus_mag/

[acsinuk]

I am not surprised just disappointed that it still hasn't sunk into cosmologists heads that we live in a 3D electric universe. In the Venus case the magnetic field will be coming through the pole tilted towards the sun and at right angles to the voltage field [represented by the H+ ionized gas in the solar wind].  The back of the planet will not have many magnetic lines as the front side.  It is the magnetic field as well as mass attraction that is binding the sun to the planet, and naturally the rotation will be in the 3rd angle; dimensionally. Remember Flemings right and left hand rules.                CliveS

[yor_on]

That one seems very complicated. We make educated guesses about the inner core of Earth, and then build theoretical frameworks, and when it comes to other planets we must guess too, although, even more.

It's very good questions though, but I don't know the answers to them. Maybe it should be placed in Geology? We have some geologists that might have better answers.
=

This one might be interesting though. The Moon.