[extropy-chat] Water Marks the Asthenosphere
hkhenson at rogers.com
Fri Jan 26 17:43:25 UTC 2007
At 07:43 AM 1/26/2007 -0500, Dan wrote:
>On Friday, January 26, 2007 4:57 AM Eugen Leitl eugen at leitl.org wrote:
> >>What about Luna?
> > Most of it was baked out during formation,
>Yes, that might be so, but what if it's not? Is there enough data on
>the lunar interior to know?
The Moon is a differentiated body, being composed of a geochemically
distinct crust, mantle, and core. This structure is believed to have
resulted from the fractional crystallization of a magma ocean shortly after
its formation about 4.5 billion years ago. The energy required to melt the
outer portion of the Moon is commonly attributed to a giant impact event
that is postulated to have formed the Earth-Moon system, and the subsequent
reaccretion of material in Earth orbit.
Today, the giant impact hypothesis for forming the Earth-Moon system is
widely accepted by the scientific community. In this theory, the impact of
a Mars-sized body (which has been referred to as Theia or Orpheus) into the
proto-Earth is postulated to have put enough material into
circumterrestrial orbit to form the Moon. Given that planetary bodies
are believed to have formed by the hierarchical accretion of smaller to
larger sized bodies, it is now recognized that giant impact events such as
this should be expected to have occurred for some planets. Computer
simulations modeling this impact can account for the angular momentum of
the Earth-Moon system, as well as the small size of the lunar core.
Unresolved questions concerning this theory are the relative sizes of the
proto-Earth and impactor, and the proportion of material from the
proto-Earth and impactor that contribute to making the Moon. The formation
of the Moon is believed to have occurred at 4.527 ± 0.01 billion years,
about 30 to 50 million years after the origin of the solar system.
>If large amounts of water can be
>incorporated into Earth's mantle and not baked out, might not something
>similar be true about Luna?
The stuff that made up Luna's mantle got baked *really hot* in a vacuum
before it aggregated into the moon. That's why it is so dry.
See also http://en.wikipedia.org/wiki/Giant_impact_hypothesis
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