[meteorite-list] Scientists find most Earth-like planet yet

[Sterling K. Webb]

Hi, Francis, Paul, List,

    Just a genteel quarrel with the assertion that
photodissociation is what removed H2O from
Venus. That certainly is one proposed theory.
It's really hard to get the numbers to support it
though. Even though it's the oldest theory (40
years or more), a good demonstration of it
has not been made.

    Grinspoon describes the decades of attempting
to computer-model these mechanisms on Venus
as "very unsatisfying." All the computer models
yield an unstable climate, one in which runaway
cooling is as likely as runaway heating! All tiny
changes in any input results in catastrophe change
of one kind or another.

    And the photochemical model fails to explain
any of the other oddities of the atmosphere (go
look at argon isotopic abundances) and actually
contradicts others.

    Of course, it hard to get any theory to fit
Venus and its numbers, whatever the theory.
And there have been some wild theories. There's
the "turnover" theory. That says that every billion
years or so, the entire crust is "turned over" and
the hot molten interior flows out and covers the
surface with a brand new crust, releasing huge
amounts of volatiles in the process. In between,
nothing happens. It doesn't explain (contradicts)
the lack of H2O, the shortage of sulfur, the high
abundance of CO2, the odd noble gas ratios.

    Francis says:

> On Earth, a Venusful of carbon dioxide is locked in
> limestone--the most abundant sedimentary rock.

    An odd coincidence, isn't it? Just like Earth...
Imagine that a warm wet world with seas and water 
and a "normal" atmosphere was massively bombarded
during a short geological time-frame by a very large
number of major impactors -- big ones, 50 km and
up, lots of them, and a few really big ones, 500 km
or more. Possibly it would begin with a huge hit by
a very large object and finish with sweeping up most 
of the fragments left co-orbiting the planet.

    The existing atmosphere would be blasted off into
space; liquid volatiles like H20 would be instantly 
vaporized and also blown off the planet along with
the original atmosphere. Multiple big impacts would 
melt the crust of the planet down to a depth of many 
kilometers, perhaps down to the mantle. 

    Surface materials like carbonate rocks would 
devolve into a massive new CO2 atmosphere, 
as would other volatile elements in the crust; the 
sheer mass of impactors would contribute a measurable 
amount of exotics, like odd isotopes of noble 
gasses to that new atmosphere... And the result 
would be a lot like an odd place called Venus.


Sterling K. Webb
-----------------------------------------------------------
----- Original Message ----- 
From: "Francis Graham" <francisgraham at rocketmail.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Wednesday, April 25, 2007 2:15 PM
Subject: Re: [meteorite-list] Scientists find most Earth-like planet yet


  Venus became hot by loss of its water vapor. An
early high convective troposphere carried Venus' water
vapor to altitudes where solar UV would dissociate it,
thus there was no water to dissove the carbon dioxide
into oceans and then lock it in sedimentary rock. On
Earth, a Venusful of carbon dioxide is locked in
limestone--the most abundant sedimentary rock. Our
troposphere did not extend high enough to
photodissociate the water vapor.
  What happened on Venus cannot happen on this new
planet because a red dwarf star does not produce
enough UV. 
  Still, there are many possibilities otherwise than a
New Earth, so Paul's point is well taken even if he
used the wrong counterexample. I would be much more
salivating if they detected--as the said they may in
the future--water.

Francis