Planet formation

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by johnduff</i>
<br />1) In the tvf book "dark Matter...", first edition, pp. 255, the statement is made "...most of the original iron in Venus ... was forced up into the crust by an excessively high spin rate." I have trouble accepting this process, because for the iron to settle towards the surface, the spin rate would have to be well over the critical spin rate where centrifugal force is equal to the gravitational force. Venus should have split long before such a state could come into existance.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">It requires overspin, not just reaching the critical spin rate, to produce fission because of the cohesive strength of the materials involved. The increased spin rate is caused by the planet or moon cooling and contracting. During contraction, the light elements are easiest to move, and tend to get squeezed toward the center (when overspin exists), while the heavy elements tend to stay in place at large radii as the surface contracts toward them.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">2) I intuit that the tidal interaction between the Earth and the Moon would be stronger, with evolution occuring much faster, than if the Earth is considered to be a solid body. Is this intuition valid?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Even standard theory says that tidal pumping melted the Earth until 3.9 billion years ago, when the first solid rocks formed.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">3) ... an abrupt spin-up of the core (from the contraction of the iron) would also be expected. This sudden contraction of the entire Earth (with a corresponding increase in spin rate) may have been the time when the Moon spun off and became a satellite. Does anybody think this visualization has any merit?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Possibly so. A phase change would definitely make the fission occur rapidly. -|Tom|-

tvf:

Thank you for your response. I appreciate it.

Re your remarks to my 2): My point here is that the Earth today is essentially a liquid body, and has probably been in this state since it first formed. Earth tidal effects are caused by hydrolic interactions, not mechanical stress-strain mechanisms. The height of a crustal deformation (solid body tide) is not governed by the strength-stiffness of the crust, but by the flow of the magma upon which the crust is floating (as in skim ice floating on a deep lake).

You plausibly state in your book that tidal interactions between solid bodies is less efficient than between liquid bodies, which are less efficient than between gaseous bodies. I am suggesting that the Earth-moon tidal evolution (increasing Moon orbital radius, and Earth "spin-down") may have occurred significantly faster than is usually imagined.

John Duff