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Titan surface image



 
 
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  #11  
Old January 21st 05, 02:39 AM
John Popelish
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Rodney Kelp wrote:

How do you get a nitrogen atmosphere from a moon that has methane oceans?


It is so cold that the methane does not have a very high vapor
pressure, so the atmosphere can keep only a little mixed in as vapor
before it rains out. Nitrogen is left. If it was a bit colder, that
would rain out, too.

--
John Popelish
  #12  
Old January 21st 05, 07:49 AM
Hud Nordin
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In article ,
Robert Hartwick wrote:
On a related matter, I was expecting to see a few photos at low
altitudes (less than a thousand meters). There was supposed to be a
spotlight to facilitate this. Has anyone seen anything of these?
Were they lost? We seem to go from kilometers high directly to the
'pebbles on the mud'. Disappointing.


The descent animation at
http://www.nasa.gov/mission_pages/cassini/multimedia/pia07234.html
shows images at 2.3 km, 2.1, 1.8, 1.7, 1.5, 1.3, 1.2, 1.0, 800 m, 700 and
500.

They planned to suspend imaging a few hundred meters above the surface,
so that they would have time to transfer the final in-air shots and
other data before a possibly fatal impact.

The lamp was supposed to come on at 400 m, but it's purpose was mainly
for spectroscopy.

The Descent Imager Spectral Radiometer Aboard Huygens is a good read:
http://www.rssd.esa.int/SB/HUYGENS/docs/SP1177/tomask_1.pdf
--
Hud Nordin Silicon Valley
  #13  
Old January 21st 05, 09:11 AM
James Garry
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"Rodney Kelp" wrote in message
...
How do you get a nitrogen atmosphere from a moon that has methane oceans?


Ask the same question of Earth, how do we have a nitrogen atmosphere with
liquid water oceans?

Briefly, there's every reason to expect materials with similar boiling
points (and more importantly, molecular masses) to be present on a given
body. Loss mechanisms for the atmosphere can be absorptive (like the CO2
that was soaked up to form carbonates on Earth) or 'exhaustive' where the
material is lost from the planet by exoatmospheric escape.

So, if Titan accreted a shedload of methane in its early life (maybe...)
then there's nothing to have stopped a comparable cosmic-abundance-worth of
nitrogen being trapped too. Do a trawl for 'Lunine' and 'J.S.Lewis' for
papers (NASA ADS for starters) and ideas.

-James Garry
(ex Huygens payload tweaker)


  #14  
Old January 21st 05, 04:27 PM
Rodney Kelp
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Well, we know plants give off nitrogen at night.
What plants are on Titan?
"Paul F. Dietz" wrote in message
...
Rodney Kelp wrote:

How do you get a nitrogen atmosphere from a moon that has methane oceans?


How do you get a (mostly) nitrogen atmosphere from a planet that has water
oceans?

Paul



  #15  
Old January 21st 05, 04:29 PM
Rodney Kelp
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That might cause pools of liquid nitrogen mighten it?

"John Popelish" wrote in message
...
Rodney Kelp wrote:

How do you get a nitrogen atmosphere from a moon that has methane oceans?


It is so cold that the methane does not have a very high vapor
pressure, so the atmosphere can keep only a little mixed in as vapor
before it rains out. Nitrogen is left. If it was a bit colder, that
would rain out, too.

--
John Popelish



  #16  
Old January 21st 05, 11:44 PM
Everett Hickey
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Nitrogen is common to all terrestrial atmospheres we currently know of.

Mars has it, though only 3%. The rest is primarily co2.

Venus has it, same figure. If you take away the co2 (the vast majority, and
a primary cause of the intense pressure), you're left with a nitrogen
atmosphere only twice as thick as Earth's, so in most ways that count Venus
has quite a bit of nitrogen with no plant life possible on it.

Earth has a predominantly nitrogen atmosphere, with oxygen making up only a
5th of it and everything else negligible. Much of this is because the far
heavier methane atmosphere we used to have, along with the not
inconsiderable co2 content, have been chemically leeched out by geologic and
biological methods. Had there been no life, we'd have either an almost
entirely nitrogen atmosphere w/ higher co2 levels, or methane would not
break down well and would be a considerable atmospheric component.

Nitrogen appears to be a default when everything else is taken away (in
Earth's case, it's the only gas that isn't being stripped out on a large
scale... in Titan's case, it's the only gas that doesn't precipitate there
that we know of).


"Rodney Kelp" wrote in message
...
Well, we know plants give off nitrogen at night.
What plants are on Titan?
"Paul F. Dietz" wrote in message
...
Rodney Kelp wrote:

How do you get a nitrogen atmosphere from a moon that has methane

oceans?

How do you get a (mostly) nitrogen atmosphere from a planet that has

water
oceans?

Paul





  #17  
Old January 22nd 05, 01:45 AM
Paul F. Dietz
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Rodney Kelp wrote:

Well, we know plants give off nitrogen at night.


What other falsehoods do you 'know'?

Paul
  #18  
Old January 22nd 05, 03:19 AM
John Popelish
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Rodney Kelp wrote:

That might cause pools of liquid nitrogen mighten it?


That depends on whether the surface pressure is high enough to raise
the boiling temperature of nitrogen higher than the surface
temperature... or whether the surface temperature is lower than the
boiling temperature of nitrogen at the surface atmospheric pressure.

--
John Popelish
  #19  
Old January 22nd 05, 11:07 AM
Henry Spencer
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In article ,
Everett Hickey wrote:
Earth has a predominantly nitrogen atmosphere, with oxygen making up only a
5th of it and everything else negligible. Much of this is because the far
heavier methane atmosphere we used to have, along with the not
inconsiderable co2 content, have been chemically leeched out...


Current belief is that Earth's atmosphere never had significant methane
(or ammonia). It was always an oxidizing atmosphere, dominated by CO2.
Earth's early atmosphere almost certainly looked a whole lot like Venus's
current atmosphere, except cooler and having more water vapor. In fact,
that's what Venus's atmosphere looked like then too.

(The key difference is just distance from the Sun: Earth's surface, even
with a thick CO2 atmosphere, never got warm enough to boil the oceans. On
Venus, once the oceans started to boil, there was no going back, because
water vapor is a powerful greenhouse gas: the oceans boiled dry, surface
temperature soared, solar UV broke down the water into hydrogen and
oxygen, and the hydrogen was lost. Earth never got that hot, and the
oceans slowly converted the CO2 into carbonate rock.)

...Had there been no life, we'd have either an almost
entirely nitrogen atmosphere w/ higher co2 levels...


There probably wouldn't be a lot of CO2 left. The CO2 was taken out by
chemical processes in the ocean; life was not involved in that until the
very end.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
  #20  
Old January 22nd 05, 06:18 PM
Scott M. Kozel
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John Popelish wrote:

Rodney Kelp wrote:

That might cause pools of liquid nitrogen mighten it?


That depends on whether the surface pressure is high enough to raise
the boiling temperature of nitrogen higher than the surface
temperature... or whether the surface temperature is lower than the
boiling temperature of nitrogen at the surface atmospheric pressure.


Temperatures in the polar regions would perhaps be low enough to liquefy
nitrogen.

Titan's orbital period around Saturn is 16 Earth days, and its
rotational period is also 16 days, so even in equatorial regions things
must get even colder during the 8 days of night, perhaps low enough to
liquefy nitrogen.

--
Scott M. Kozel Highway and Transportation History Websites
Virginia/Maryland/Washington, D.C. http://www.roadstothefuture.com
Philadelphia and Delaware Valley http://www.pennways.com
 




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