Why magnetic field Earth yes, Mars&Venus no?

I was wonderin Earth's strong magnetic field which protects life and why
Venus and Mars have not one.
I thought that moons tidal waves pump crust and so keeps .... that thing
between crust and core ...liquid and that's why strong field...but...

"Aidan Karley 10 june 09:56 wrote
The flexure of the Earth's crust by lunar tides probably does have
a heating effect. But if there were significant transfer of energy from
Moon's orbiting to Earth, then the Moon would be receding from Earth at a
faster rate than is observed.
Radiogenic heating is orders of magnitude more significant than
tidal flexure."

So, how about moon making field stonger by keeping spinning of core and
crust more asyncronous?
And crash of Moon and Earth gave extra supply of ironcore and heavy
radioactive metals?
By this I'm just asking that is it needed to have that kind of accidental
crash and rare (just supposed) double planet system like Earth-Moon to keep
4 billion old magnetic field strong enought to protect life above crust,
under open skies?
I'm just worried how common is techno-civilised life in space, because
nobody hasn't heard any babbling lately?

Hetu

"Heikki Tuhkanen" wrote in message
...
I was wonderin Earth's strong magnetic field which protects life and why
Venus and Mars have not one.

The processes are not fully understood:

Venus' slow rotation
Mars Solid Core
Earth fast rotation and liquid outer core.

Thus begins my education......

Regards


Chris

I believe Mars has a weak Mag Field,

Simon
"Chris Taylor" wrote in message
...

"Heikki Tuhkanen" wrote in message
...
I was wonderin Earth's strong magnetic field which protects life and why
Venus and Mars have not one.

The processes are not fully understood:

Venus' slow rotation
Mars Solid Core
Earth fast rotation and liquid outer core.

Thus begins my education......

Regards


Chris

Hayley wrote:
I believe Mars has a weak Mag Field,

The Earth has a magnetic field at the equators of about 30,000
nanoTesla (3 x 10^4nT). Venus has a residual field of ~10^-5 of Earth's
(0.3nT) and Mars about ~ 10^-4 (3nT). Those fields are insufficient to
protect Mars and Venus from the solar wind and radiation. Partially,
these weak fields are induced by interaction between the solar wind and
the planetary bodies orbiting through the electric and magnetic fields
generated by the solar wind.

http://www-ssc.igpp.ucla.edu/personn...pers/mars_mag/
(~10-^4)
http://www-ssc.igpp.ucla.edu/personn...ers/venus_mag/
(~10-^5)

One suggestion is that Venus lacks a strong dynamic magnetic field
because Venus has no plate tectonics. The supposed mechanism by which
plate tectonics aids in generating a strong dynamic field is the plate
movements allows enough heat to escape quickly enough that an internal
dynamo can be maintained by convective currents. But Venus has no
tectonic plates, a sign of convection and "stirring." Absent plate
tectonics, heat cannot be radiated away fast enough, there are no
convective currents in the mantle, and thus, no dynamic field.

http://www2.ess.ucla.edu/~nimmo/website/paper25.pdf#search='magnetic%20field%20Venus'

Venus is about as large as the Earth. Earth's magnetic field is thought
to be generated in part by the differential rate of rotation of the
outer and inner portions of the Earth's interior. Venus is large enough
to generate a dynamic field by this differential rotation and and
"stirring" the outer core, like the Earth does. Venus's rotation period
is about 243 Earth days. But "It is important to note that, contrary to
popular belief, dynamo theory does not credit the smallness of the
magnetic moment to the slow rotation of Venus . . ."

http://www-ssc.igpp.ucla.edu/personn...ers/venus_mag/

Mar's archean magnetic field (thought to be ~ 1,000nT) is now gone and
currently is similar to Venus's weak field. Probably the Martian core
cooled. Mars is smaller than the Earth and cooled faster. But Mars
currently rotates at comparatively the same rate as the Earth (a
Martian day is about 40 minutes longer than an Earth day). Mars would
be a candidate for generating a dynamic field by differential rotation
and "stirring." But Mars does not generate a dynamic field.

http://www-ssc.igpp.ucla.edu/personn...pers/mars_mag/

A nice study in contradictions in comparative planetary geophysics.

- Canopus56