Hi,
Venus they're not sure about.
One thing I think we can be sure about is that
no one will ever use the phrase "so darn cold"
about Venus, as we stand next to a small creek
running with liquid lead and other low melting
point metals...
There are signs that may be recent activity on
Venus in some areas, but interpreting them
is in dispute. Generally, the surface of Venus
appears to have formed all at one time, crater
dated at 480 +/- 80 million years ago. The lack
of long-term change is attributed to the fact
that Venus's crust is, compared to the Earth's,
extremely thick and rigid, with no detectible
tectonic movement, recent mountain building,
or any of the other features of a "terrestrial"
planet. But, given the similarity in size, density
(and hence composition) to the Earth, few doubt
that Venus' core is as hot and active as our own.
It's just that nothing (much) can punch its way
through that heavy crust.
Sterling K. Webb
----------------------------------------------------------------
----- Original Message -----
From: "Rob McCafferty" <[email protected]>
To: <[email protected]>
Sent: Saturday, September 05, 2009 7:00 PM
Subject: Re: [meteorite-list] Slow cooling rate of irons in space
The "so darn cold" thing refers to objects not being lit/heated by their
star. Day sides will heat up until they radiate more heat than they
absorb. Night sides will cool as quickly as physics (and any atmosphere)
allows.
If one face of Mars stayed pointing at the sun all the time, it would be
quite warm on a permanently daylit side. It attains 20degC at the
equator during the day as it is.
Given that the only method of heat transfer is conduction, requiring
direct contact of atoms, until you get to the surface where they can
radiate heat away, it seems more reasonable that a moderately sized body
may keep a hot core warm for a very long period of time. Particularly if
you have the core covered with a crust made of poorly adjoined
fragements of rock, acting as a blanket possibly hundreds of km deep.
The physics of the planetary cooling has long been worked out. For me,
the amazing thing is just how the mass of the planet changes the cooling
time.
Mars is believed to have stayed hot enough to keep it's volcanoes going
until 1Ga ago. Now it's interior is too cold.
Smaller bodies generally stopped being active much earlier. Venus
they're not sure about.
Rob Mc
Rob McC
--- On Sun, 9/6/09, Pete Shugar <[email protected]> wrote:
From: Pete Shugar <[email protected]>
Subject: Re: [meteorite-list] Slow cooling rate of irons in space
To: "Carl 's" <[email protected]>,
[email protected]
Date: Sunday, September 6, 2009, 12:34 AM
May I please inject just the one
comment?
In space, the side facing the star (in our case, the sun)
can get quite hot, ie close to the sun --hotter, and further
away---less hot.
Conversly--the side away from the star can approach very
high negative degrees, ie 250 to 400 below zero.
This is the "so darn cold" you were thinking about.
Pete
----- Original Message ----- From: "Carl 's"
<[email protected]>
To: <[email protected]>
Sent: Friday, September 04, 2009 8:18 PM
Subject: [meteorite-list] Slow cooling rate of irons in
space
Hi Elton and All,
I've read about the very slow cooling rate of the molten
iron in various books but I don't understand why this is so.
Why would it take millions of years for just a few drops of
degrees? It's hard for me to envision this even accounting
for bombardments and radioactive decay. Radioactivity from
the original super nova event, right? Maybe it's
because I think of space as being so darned cold it wouldn't
take anything long to lose heat and freeze up. I realize
radioactivity takes a long time to decay but would it take a
lot or so little to keep a large planetary body hot for so
long? Thanks.
Carl
Eman wrote:
> I think this theory has a potential fatal flaw if what
we think we know about
taenite/kamacite growth is valid. Without an insulating
blanket the molten
pool will not exist in a molten state long enough to permit
crystallization aka
Widmanstatten patterns.
Be it remembered that Widmanstatten pattern/crystal growth
is very very slow on
the order of 10's of degrees cooling per million years. It
is difficult to
develop a scenario that integrates a large crater on an
Goldilocks Asteroid
which works.. ..
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