Mars once had atmosphere ... why not now?

Mike Dworetsky wrote:

"Joe Schmoe" wrote in message
...
Hej Llanz,

Why is Earth's magnetic field pole shift 200K years delayed? Maybe OUR
magnetic field is weakening quickly and our atmosphere is about to be
blown off, and we'll have to migrate (maybe for the third time) to
another planet that "looks too hot" and "couldn't possibly harbor life".
I guess we just have to redirect as many incoming comets onto Venus'
surface and wait a few hundred k years, and create a Noah's Ark, and
hunker down in the meantime.


Paleomagnetic evidence tells us that the magnetic reversals do not occur at
strictly regular intervals, and that when they do, the duration of "zero
field" is short compared to the duration of "strong field". Even when the
field reverses, there is a net local field here and there due to the
self-excited dynamo in the Earth's iron core; its average value is
approximately zero for a while (+ in some locations; - in others), but
locally it may not be zero.

It would take a very long time for the relatively weak solar wind to strip
off the entire atmosphere (many millions of years). When the solar system
was very young, the wind was probably a lot stronger and had a significant
effect.
Venus has no magnetic field and the solar wind is stronger there.
Why does it still have an atmosphere ?



--
http://www.geocities.com/carla_sch/index.html

"Carla Schneider" wrote in message
...
Venus has no magnetic field and the solar wind is stronger there.
Why does it still have an atmosphere ?



--
http://www.geocities.com/carla_sch/index.html

Bigger planet than Mars, more gravity, molecules in the atmosphere have
a higher escape velocity.

rj

[Regarding magnetic fields and retention of atmospheres:]

"CS" == Carla Schneider writes:

CS Mike Dworetsky wrote:

It would take a very long time for the relatively weak solar wind
to strip off the entire atmosphere (many millions of years). When
the solar system was very young, the wind was probably a lot
stronger and had a significant effect.

CS Venus has no magnetic field and the solar wind is stronger there.
CS Why does it still have an atmosphere ?

Because the magnetic field is only part of the equation. More
important are the planet's mass (gravity) and mean surface
temperature. The typical velocity of an atmosphere molecule (which is
determined by the mean atmosphere temperature) is less than the
Earth's escape velocity (by a significant amount, IIRC).

In contrast, Mars has a much lower mass (gravity) so its escape
velocity is lower, which means that the difference between escape
velocity and typical atmospheric molecular velocity is less. Thus,
much of the Martian atmosphere could leak away over the life of the
solar system.

Venus has a mass comparable to Earth. Even though its mean surface
temperature is much higher, that's not enough to increase the
molecular velocity close to the escape velocity. Thus, Venus has held
onto its atmosphere. (Of course, Venus also has a *lot* more
atmosphere to lose.)

--
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Little Reason,

Why doesn't Venus have a magnetosphere now?

That was the primary question. Not global warming on Earth, not the
loss of Mars' magnetosphere.

And I made a response that was perhaps instructive to understanding the
question.

Let's look at this simple fact - Venus rotates on its planetary axis
very slowy, did you mention that factoid? It's a very obvious fact
about Venus' lack of magnetosphere. Shouldn't you be helping folks to
understand what you understand, or are you NSA NAZI death farts making
us all dumb and drink more Coke and Pepsi?

JS

Greg Crinklaw wrote:

call anyone a
dumbass with little reason.

Hej Mikey,

This one (after 20 regular cycles of 70k years) is 200k years delayed.
And I must say that you are as good a liar as the Bush family males.
Are you a Bush family male?

Yes, zero field has been longer and longer even during the expected
cycles of 70k years. *If* another cycle occurs the zero cycle will
probably be 2000 years long.

JS

Mike Dworetsky wrote:

Paleomagnetic evidence tells us that the magnetic reversals do not occur at
strictly regular intervals, and that when they do, the duration of "zero
field" is short compared to the duration of "strong field".

Let's say something about volcanism. Past and future, and atmosphere,
and life depending on plate tectonics, etc. Venus doesn't spin fast, it
wouldn't take much to make it do so; or let me grep a moment and say
that perhaps if we leaked a weak Ionian moon into Venus orbit.. I
suppose that has been wafted into hierarchies of blownswelled minds
before - but *I* just thought of it.

As for the sonolum folks who finally found my archives of love letters
to Claudia Eberlein *kiss*, and made a workable device. Try this liquid
synthesis of polar density. Water, alcohol, and JLo.

JS


Joseph Lazio wrote:
Venus has a mass comparable to Earth. Even though its mean surface
temperature is much higher, that's not enough to increase the
molecular velocity close to the escape velocity. Thus, Venus has held
onto its atmosphere. (Of course, Venus also has a *lot* more
atmosphere to lose.)

Joe Schmoe wrote:
Let's look at this simple fact - Venus rotates on its planetary axis
very slowy, did you mention that factoid? It's a very obvious fact
about Venus' lack of magnetosphere. Shouldn't you be helping folks to
understand what you understand, or are you NSA NAZI death farts making
us all dumb and drink more Coke and Pepsi?

Sorry, you lost me when you called the guy a dumbass for no good reason.
I don't have time to play with someone that rude.

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools Software for the Observer:
http://www.skyhound.com/cs.html

Skyhound Observing Pages:
http://www.skyhound.com/sh/skyhound.html

To reply remove spleen

MarsMud wrote in message news:AZn1c.55925$A12.11752@edtnps84...
OK. So NASA has evidence that Mars once had lakes/seas of water. This
means it was warmer and had more of an atmosphere at some point in the
past. Why then and not now? What changed? Can it happen to earth?

Your thoughts are appreciated.

I have a theory. If you examine the topographic map you can see that
the Hellas Basin is the result of a very large impact. Several hundred
millenia ago, we may have seen Mars as having a very large, partially
melted northern ice cap that covered much of the northern hemisphere
with frosty, crystal-clear waters. There was a single moonm then,
Hellas, which finally drew close enough to begin a final descent into
the Southern Hemishere. So much energy resulted that it may have
looked like that freeze-framed image of a bullet exiting an apple,
sending most of the former ocean flying off of the opposite side of
this low-G planet. Current moons Phobos and Deimos may have slowly
accreted from this material, leaving behind a world without most of
its H2O.

Hej GC,

Yur Momma was a DA.. Yur made of sugar. Uhnn, OK, so I called him a
dumbass for no good reason. Should I apologize? I didn't mean to hurt
anyone's feeling's when what is the possibility of life and death of
humanity is at stake here. Sonoluminescent fusion? NAH! Exxon/Mexxons
are the future!

JS

Greg Crinklaw wrote:

Joe Schmoe wrote:

Let's look at this simple fact - Venus rotates on its planetary axis
very slowy, did you mention that factoid? It's a very obvious fact
about Venus' lack of magnetosphere. Shouldn't you be helping folks to
understand what you understand, or are you NSA NAZI death farts making
us all dumb and drink more Coke and Pepsi?


Sorry, you lost me when you called the guy a dumbass for no good reason.
I don't have time to play with someone that rude.

In article ,
says...
MarsMud wrote in message news:AZn1c.55925$A12.11752@edtnps84...
OK. So NASA has evidence that Mars once had lakes/seas of water. This
means it was warmer and had more of an atmosphere at some point in the
past. Why then and not now? What changed? Can it happen to earth?

Your thoughts are appreciated.

I have a theory. If you examine the topographic map you can see that
the Hellas Basin is the result of a very large impact. Several hundred
millenia ago, we may have seen Mars as having a very large, partially
melted northern ice cap that covered much of the northern hemisphere
with frosty, crystal-clear waters. There was a single moonm then,
Hellas, which finally drew close enough to begin a final descent into
the Southern Hemishere. So much energy resulted that it may have
looked like that freeze-framed image of a bullet exiting an apple,
sending most of the former ocean flying off of the opposite side of
this low-G planet. Current moons Phobos and Deimos may have slowly
accreted from this material, leaving behind a world without most of
its H2O.

Interesting theory, and it may have quite a bit of merit on its general
assumption (that impact may have played some kind of a role in the loss
of Martian volatiles). However, Hellas probably wasn't involved.

According to Peter Cattermole's comprehensive book, "Mars: The Mystery
Unfolds," the best estimates place Hellas as one of the oldest of the
Martian impact basins. While it's impossible to affix a solid date to
the Hellas event without impact melts in hand for radioisotopic dating,
geologist Mike Carr has estimated that Hellas was formed roughly 3.8
billion years ago (note -- I use the American definition of "billion" in
my discussions). That's about the same age as the Imbrium basin event
on the Moon. The northern lowlands, dated using a number of techniques,
are younger than that.

Since there is evidence that the large-impact (i.e., basin-forming)
event rate declined drastically across the entire solar system about
three billion years ago, it would make sense that most of Mars' basins
were formed in the first half-billion to billion years of its existence.
Hellas certainly seems to have been. And the terrain altered by what
appears to be both running water and standing water on Mars is quite a
bit younger than that -- more like one to two billion years at the
oldest (and some seems *much* younger). (All, of course, with the
caveat that absolute dating is impossible without samples.)

According to studies of the Martian upper atmosphere and its interaction
with the solar wind, Mars loses roughly one to two kilograms of
volatiles (i.e., air and water) per *second*. The observed rate of
volatiles loss means that Mars could lose *all* of its volatiles before
the Sun goes into its red giant phase, i.e., in the life of the solar
system. So, it doesn't take a huge "whack" to rid Mars of most of its
water -- it just takes a lot of time.

And Nature is patient.

As for Hellas (or any of the other basins) being formed by a moon whose
orbit has deteriorated -- that seems less likely. The velocities would
be too low for a basin-forming event; a moon would break up due to tidal
effects as it spiraled in and impact as millions of smaller bodies.
That kind of thing doesn't tend to make basins, it tends to make
millions of craters of all sizes. Basins are made by mountain-sized
asteroids traveling at cosmic velocities, not by moons that have (for
some reason) spiraled in.

Besides, the best guesses about Phobos and Diemos at this point are that
they are asteriods that were somehow captured by Mars, and are not the
result of a basin-forming impact. The materials of the moons (based on
remote sensing) seems identical to other asteroids, they don't show the
kind of alteration you would expect if they were created during a basin
impact event. (In specific, their spectra tend to place them in the
same class as objects from the outer asteroid belt, closer to Jupiter
than Mars.) Of course, that's all based on remote sensing; it would be
*very* instructive to get some in-situ measurements of Phobos and Diemos
rocks and dust, as well as materials from other asteroids, to settle
some of the questions about the moons' origins.

Doug