View Full Version : Why a Venus atmosphere?

2004-Oct-01, 11:18 AM
Mars has a very thin atmosphere. One of the reasons supposedly is because it lacks a magnetic field
of any significance (which could protect its atmosphere from being blown away by the solar wind).
But Venus has no particular magnetic field either while still enjoying a rather thick atmosphere.
Is the gravitational pull really enough to explain this 'anomaly'? Don't forget that being much
closer to the Sun it is significantly more 'windy' near Venus than in the vicinity of Mars. So,
how come?

2004-Oct-01, 03:10 PM
Because the Venus atmosphee itself is probably just incredibly condensed solar wind.

John L
2004-Oct-01, 03:52 PM
I think it has to do with Venusian volcanism. Venus is supposed to be extremely geologically active with the entire surface of the planet resurfaced not too logn ago (geologically speaking) and possibly every billion years or so it happens again. The outgasing of the planet through that volcanism should add huge amounts of carbon and sulphur to the atmosphere, which is what we see there now.

Why is Venus so volcanic? I think either a major impact with Venus blew it apart and it coallesced back together into the slow retrograde rotating world we see today. Maybe that total planetary resurfacing was Venus' former moon finally crashing into its surface. Maybe Venus was once tidally locked with its own large moon and the impact finally knocked it into a retrograde rotation. Maybe Venus is just so hot because its day is longer than its year. That's why sending probes like VE is necessary. The only way we can answer these questions is by going there and looking for clues that point to the possible answers.

2004-Oct-02, 09:25 AM
Actually, the idea that the atmosphere of Venus is 'incredibly condensed solar wind' wouldn't
work since solar wind is almost entiryly protons and alfa particles while the venusian
atmosphere is mainly sulfur, carbon and oxygen. Of course there's a lot of helium and hydrogen
too. However, I found an article on space.com that gives some hints though. (See
http://www.space.com/scienceastronomy/venu...ife_040826.html (http://www.space.com/scienceastronomy/venus_life_040826.html) ) It actually touches
on the geology suggesting that from time to time Venus surface gets reshaped (see the article for
details) spewing out a lot of sulfur and carbon. As it turns out hydrogen being so light does actually
get blown away far easier than other atoms/molecules. So I guess, I kinda answered my own
question: both gravity and geological activity could be the reasons for an atmosphere
existing on Venus.

So in order to terraform Venus you would probably both need to spin up the rotation
of the planet (to get a magnetosphere) and rid it of the sulfur compounds while filling it with
water and oxygen. That would probaly take a lot of energy. And even after that it
would be probably quite a stinky place for ages. Sigh... But I still belive Venus would make
a better goal for human colonization than for instance Mars. At least in the long run.

2004-Oct-05, 05:29 AM
That is a very nice article summing up the best theories of the very limited knowledge about the geologic history of Venus and also of its atmosphere.
My own thoughts about terraforming Venus would start with cooling it first. Deploy a very large canopy of material in synchronous orbit to reflect the majority of sunlight reaching the atmosphere. This canopy could be adjusted to heat or cool the atmosphere as needed to achieve the best effect: retaining some atmosphere while forcing the rest to condense and rain back upon the surface. The next step would involve diverting a few (very) large comets from the outer reaches of the solar system to add much needed water. Then add a whole lot of plants in the high and dry areas with some means of reducing the acidity of the water that would exist and you then have oxygen from the abundant carbon dioxide. Then you just have to hope that the whole thing isnt ruined by the next massive upwelling of magma and catachlysmic volcanism resulting from this from a mantle deprived of plate tectonics.

2004-Oct-05, 10:21 AM
Actually, I wasn't suggesting any particular timeline. I belive that cooling should go first since
that would make the planet more workable. Also, hitting it with comets could be used for
(some) spinnig up of the rotation. But that would probably not give very much. However,
some kind of protection from the solar wind will be necessary if we don't want to lose
the water as soon as we manage to introduce it into the atmosphere.

There are two ways of addressing this problem as I see it. Either to use some kind of
material barrier (like the one you are suggesting) that would both block out the sunlight
and the solar wind. Another would be to create an artificial magnetic filed on a planetery
scale. The thing with the magnetic field could also be used to influence the rotation too
since the solar wind is actually a stream of charged particles ie electric current. Maybe. I'm
not much of an astrophysist so it's hard for me to tell whether that could have any
marked effect.

As far as cooling of Venus is concerned there is one more thing to consider (well, probably
many, but only one major springs to mind right now). Stopping it from receiving excesive heat
is fine but we should make it start losing some as well. This would problably mean reshaping
the chemistry of the atmosphere in such a way that it would get more transparent to the IR
radiation. This means getting rid of the greenhose gases. In this case we are talking almost
exclusively about carbon dioxide. The most obvious way would be to split the molecules
and bind carbon somehow (or just pile it up, it wan't go anywhere). This way you would
enrich the atmosphere with oxygen, making it cool faster at the same time. This could be
acheived either by deploying large/many atmosphere remaking plants all over the place
or by the use of nano technology filling the 'air' with small mechanical bugs that would
do the job in quite. How about that, a whole industry in the making. Cool. Anybody who
knows a financier with an open mind?.. ;-)

(I'm a man of few words but, gee, once I get going...)

2004-Oct-05, 10:02 PM
Hi All

Why does Venus have an atmosphere when Mars doesn't?

Atmosphere is lost in several ways.

(1)It can boil away from the exosphere - a process known as Jeans Escape. Ironically a carbon dioxide atmosphere cools its exosphere so this doesn't happen on Mars or Venus. Nitrogen/oxygen heat up the exosphere because of their radiative properties

(2)Nitrogen recombination - monatomic nitrogen gains a lot of energy by recombining causing it to escape small planets.

(3)Solar wind pickup - not really effective now for heavy gases, but highly effective when the Sun was young.

Simply because it is so much bigger than Mars Venus' gravity well, almost as big as Earth's, means impact erosion can't blast air into space nor can recombination of nitrogen cause it to fly off into space either. Mars' gravity is enough to hang on to heavy gases like carbon dioxide against leakage from the exosphere via Jeans escape too, but ultraviolet dissociation of water means hydrogen is still escaping.

I think the fact solar-wind pickup didn't erode Venus' atmosphere is significant. What it probably means is that before Venus' oceans leaked away it had a significant magnetic shield. Once the oceans fled and Venus hotted up - sometime after the solar wind died down - the carbonates that once trapped the CO2 decomposed making the current dense atmosphere. This braked Venus' rotation and that caused the electromagnetic currents in the core to die off. Thus modern Venus was born.


2004-Oct-06, 09:16 AM
Once the oceans fled and Venus hotted up - sometime after the solar wind died down - the carbonates that once trapped the CO2 decomposed making the current dense atmosphere. This braked Venus' rotation and that caused the electromagnetic currents in the core to die off. Thus modern Venus was born.

I would think it was the other way around. Once the rotation slowed down and the magnetosphere
went away, the hydrogen started escaping drying the planet up. This lead to heating up of the planet
and possibly more violent geological activity. Keep in mind that Venus is in a slow retrograde rotation
which would be unikely to have been caused by the viscosity of thick atmosphere. This phenomenon
does seem to require some colision with another large body. Such a colision would have blown away
a lot of the atmosphere and if it happened after all those comets were cleaned away from our solar
system there would be no source of new water. This sounds more plausible to me.

However, another scenarion appears possible. Suppose the planet did get a thick atmosphere that
slowed down the rotation to more or less standstill. If it got hit by something then, it would require
much less energy to start its retrograde rotation.

I guess all of this calls for some model to test on a computer. Not mine, though. :-( My feeling is
that the first model is more likely, however.

2004-Oct-07, 05:31 AM
Hi All

Adam, the atmospheric braking of Venus has been extensively studied and the mildly retrograde rotation is one possible end state. Here's a link...
Big ADS Link (http://adsabs.harvard.edu/cgi-bin/nph-ref_query?bibcode=1977A%26A....60...85K&refs=CITATIONS&db_key=AST)

...as you can see there are a few articles at least discussing Venus' atmosphere and rotation. Venus' massive resurfacing in the last billion years has pretty much scrubbed it of any clue. We can only apply physics as we know it and see what happens to our models.


2004-Oct-07, 07:56 AM
Ehum... It'll take some time to read these since I don't have much spare time (family,
master's thesis and a full time job don't leave much room for other activities). If you have
a pointer to some more easily digestable article that elaborates on these matters it
would be much appreciated. I admit though that you have a strong case.

2004-Oct-07, 12:24 PM
Hi All

Adam wrote...

If you have a pointer to some more easily digestable article that elaborates on these matters it would be much appreciated. I admit though that you have a strong case.

...have a look at the abstracts for the articles for starters. Always an easy intro.


BTW cool name