Toxic atmosphere in "Avatar"
Phillip Thorne
movie "Avatar," but there are scientific elements of interest (and
that don't stretch credulity like "unobtanium" and "morphic
resonance"). They're not explained *in* the movie, so you have to
refer to off-screen references. Among the tie-ins, the closest thing
to a technical manual is _James Cameron's Avatar: A Confidential
Report on the Biological and Social History of Pandora: An Activist
Survival Guide_ (Wilhelm & Mathison).
In the movie, all the human characters on Pandora wear rebreather
packs (p.12) outside, because "You'll be unconscious in twenty
seconds, dead in four minutes." But why, exactly?
According to the _Survival Guide_ (pp.6, 8), the specs are these:
surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
is similar to Earth.
(How does one compute partial pressures of a gas mix based on what I
presume to be molar abudnances? I probably knew this in high school
chemistry.)
* Carbon dioxide isn't immediately toxic, but it can displace oxygen
from the lungs, according to Canada's equivalent of OSHA:
<http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide/health_cd.html>
* According to the CDC and OSHA, the immediately dangerous level of
hydrogen sulfide is 100 ppm.
<http://www.atsdr.cdc.gov/Mhmi/mmg114.html>
* And for chlorine it's only 10 ppm.
<http://www.atsdr.cdc.gov/MHMI/mmg172.html>
* Earth's atmosphere is about 1% argon, but I have to wonder about a
protoplanetary nebula rich enough in xenon to endow Pandora with 5.5%.
Maybe it's related to the vicinity of a superjovian. According to
WebElements.org, xenon is harmless unless (like CO2) it displaces
oxygen from the lungs. With an atomic weight of 131 for Xe
(monatomic, of course) vs 32 for O2, it's probably difficult to
exhale.
<http://webelements.org/xenon/biology.html>
--
** Phillip Thorne ** peth...@comcast.net **************
* RPI CompSci 1998 *
** underbase.livejournal.com ***************************
Andrew Plotkin
>
> In the movie, all the human characters on Pandora wear rebreather
> packs (p.12) outside, because "You'll be unconscious in twenty
> seconds, dead in four minutes." But why, exactly?
No oxygen, I assumed. Those are the symptoms of breathing, say, pure
nitrogen. Deoxygenated blood reaches your brain, fall down.
(I wondered what kind of chemical mix could support life without
oxygen without *also* being highly corrosive -- Pandora's atmosphere
doesn't seem to hurt human eyes. But I figured the writers hadn't
thought that far in.)
> According to the _Survival Guide_ (pp.6, 8), the specs are these:
Oh, well, if you're going include external information...
> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
> is similar to Earth.
Xenon is an excellent anesthetic, but random googling indicates that
you need 60% or more, not 5%.
I think that 18% CO2 will knock you out, but not in twenty seconds.
Conclusion: reading the _Survival Guide_ doesn't help.
--Z
--
"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
*
John Park
> People tend to get distracted by the morality play aspects of the
> movie "Avatar," but there are scientific elements of interest (and
> that don't stretch credulity like "unobtanium" and "morphic
> resonance"). They're not explained *in* the movie, so you have to
> refer to off-screen references. Among the tie-ins, the closest thing
> to a technical manual is _James Cameron's Avatar: A Confidential
> Report on the Biological and Social History of Pandora: An Activist
> Survival Guide_ (Wilhelm & Mathison).
>
> In the movie, all the human characters on Pandora wear rebreather
> packs (p.12) outside, because "You'll be unconscious in twenty
> seconds, dead in four minutes." But why, exactly?
>
> According to the _Survival Guide_ (pp.6, 8), the specs are these:
> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
> is similar to Earth.
>
> (How does one compute partial pressures of a gas mix based on what I
> presume to be molar abudnances? I probably knew this in high school
> chemistry.)
Avogadro's law: partial pressure is proportional to molar concentration.
>
> * Carbon dioxide isn't immediately toxic, but it can displace oxygen
> from the lungs, according to Canada's equivalent of OSHA:
>
> <http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide/health_cd.html>
>
> * According to the CDC and OSHA, the immediately dangerous level of
> hydrogen sulfide is 100 ppm.
>
> <http://www.atsdr.cdc.gov/Mhmi/mmg114.html>
>
> * And for chlorine it's only 10 ppm.
>
> <http://www.atsdr.cdc.gov/MHMI/mmg172.html>
>
> * Earth's atmosphere is about 1% argon, but I have to wonder about a
> protoplanetary nebula rich enough in xenon to endow Pandora with 5.5%.
> Maybe it's related to the vicinity of a superjovian. According to
> WebElements.org, xenon is harmless unless (like CO2) it displaces
> oxygen from the lungs. With an atomic weight of 131 for Xe
> (monatomic, of course) vs 32 for O2, it's probably difficult to
> exhale.
>
CO2 would make you choke; Cl2 would attack the throat and lungs; but H2S is
a nerve poison and would probably be the one to knock you out. (At very
low concentrations H2S has the infamous rotten-eggs smell, but at higher
[dangerous] levels it deactivates the sensory nerves and is odourless.)
--John Park
Mike Dworetsky
> People tend to get distracted by the morality play aspects of the
> movie "Avatar," but there are scientific elements of interest (and
> that don't stretch credulity like "unobtanium" and "morphic
> resonance"). They're not explained *in* the movie, so you have to
> refer to off-screen references. Among the tie-ins, the closest thing
> to a technical manual is _James Cameron's Avatar: A Confidential
> Report on the Biological and Social History of Pandora: An Activist
> Survival Guide_ (Wilhelm & Mathison).
>
> In the movie, all the human characters on Pandora wear rebreather
> packs (p.12) outside, because "You'll be unconscious in twenty
> seconds, dead in four minutes." But why, exactly?
>
> According to the _Survival Guide_ (pp.6, 8), the specs are these:
> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
> is similar to Earth.
If the apparently abundant plant life is engaged in photosynthesis, and life
has been evolving on Pandora for anything like as long as on Earth, I can't
understand why CO2 would still be so high. An equilibrium between O2, CO2,
and organic carbon storage should exist, with CO2 much depleted. On Earth,
most of the original CO2 is tied up in rocks such as limestone. What
fraction of Pandora is covered by oceans?
As for what would kill in 4 minutes, Chlorine gas was used as a weapon in
WW1, and H2S is poisonous in high amounts. Every once in a while a
volcanologist is overcome and sometimes killed by H2S while investigating
sulfur vents, etc.
If there is vulcanism, isn't there also going to be some (deadly) CO (carbon
monoxide)?
The Xe is just plain weird. Xe is a rare element, while argon is very
abundant in the cosmos.
> (How does one compute partial pressures of a gas mix based on what I
> presume to be molar abudnances? I probably knew this in high school
> chemistry.)
>
> * Carbon dioxide isn't immediately toxic, but it can displace oxygen
> from the lungs, according to Canada's equivalent of OSHA:
>
> <http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide/health_cd.html>
>
> * According to the CDC and OSHA, the immediately dangerous level of
> hydrogen sulfide is 100 ppm.
>
> <http://www.atsdr.cdc.gov/Mhmi/mmg114.html>
>
> * And for chlorine it's only 10 ppm.
>
> <http://www.atsdr.cdc.gov/MHMI/mmg172.html>
>
> * Earth's atmosphere is about 1% argon, but I have to wonder about a
> protoplanetary nebula rich enough in xenon to endow Pandora with 5.5%.
> Maybe it's related to the vicinity of a superjovian. According to
> WebElements.org, xenon is harmless unless (like CO2) it displaces
> oxygen from the lungs. With an atomic weight of 131 for Xe
> (monatomic, of course) vs 32 for O2, it's probably difficult to
> exhale.
>
> <http://webelements.org/xenon/biology.html>
--
Mike Dworetsky
(Remove pants sp*mbl*ck to reply)
TBerk
> According to the _Survival Guide_ (pp.6, 8), the specs are these:
> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
> is similar to Earth.
>
I'm disappointed to find out a 'official' publication is relating the
atmosphere is near Earth like. I'm thinking it would need to be very,
very thick to support the flying reptiles, With Rider, as shown in the
film.
(Here is a thought; how much O2 would be too much? maybe the
atmosphere is _too_ 'beneficial' for Terrestrials? )
But as published it's "enough Oxygen, Too much Carbon-Dioxide...".
bah.
berk
rochrist
Remember that the gravity is somewhat less than earth normal as well.
Bryan
> (Here is a thought; how much O2 would be too much? maybe the
> atmosphere is _too_ 'beneficial' for Terrestrials? )
How much O2 is too much depends on a lot of factors.
But the first thing to keep in mind is toxicity of a gas is generally
determined by its partial pressure. For example, our atmosphere has a
pressure of 1ATA, and its 20% O2, so the partial pressure of O2 (pO2)
in our atmosphere is 1ATA *0.2 = 0.2ATA.
At earthly pressures (1ATA) 100% O2 (i.e. a pO2 of 1ATA) will cause
lung damage and inflammation if you're exposed to it for too long
(days), and in theory could be fatal, although AFAIK this has never
happened. SCUBA divers using O2 enriched air do occasionally die from
oxygen toxicity - generally speaking a pO2 of 1.4ATA is considered
dangerous (over time it leads to seizures & unconsciousness), at
1.6ATA bad things are guaranteed (immediate seizures and
unconsciousness). A pO2 of 2.0ATA or higher is generally considered
to be "instantly" lethal.
To put that into context, a pO2 of 1.6ATA is:
-100% O2 at 1.6ATA
-50% O2 at 3.2ATA
-20% (or atmosphere) at 8ATA
If I recall correctly, pO2's of 0.5 and lower are considered
completely safe, and 1.0 and lower are tolerable for moderate periods
(a few days). This means that 100% O2 at 0.5ATA is theoretically
survivable for a lifetime.
One thing I would add though - 18% CO2 would likely induce rapid
unconsciousness and death, not due to O2 starvation, but rather due to
the way our bodies respond to elevated CO2 levels. Our bodies do not
detect O2 directly, but rather use CO2 levels as a proxy. In
addition, because our bodies make CO2, we don't absorb it from the
air. Rather the levels in air determine the efficiency at which our
lungs release the CO2 made by our bodies. The combination of this is
that relatively low levels of CO2 can kill; by preventing CO2 exchange
(which causes acidosis of the blood and can also decrease O2 exchange)
and through the physiological effects (i.e. the things our brain makes
our bodies do when it detects too much CO2). Generally speaking, 1%
causes drowsiness, by 5% people will be in distress (elevated blood
pressure and heart/breathing rate), at 7-10% the physiological
response is so severe that seizures and unconsciousness are common.
Somewhere around 15-20% CO2 becomes lethal, due to our bodies response
and and the effects of CO2 on O2 exchange in the lungs.
Bryan
TBerk
> TBerk wrote:
> > On Jan 18, 7:06 pm, Phillip Thorne <petho...@comcast.net> wrote:
>
> >> According to the _Survival Guide_ (pp.6, 8), the specs are these:
> >> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
> >> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
> >> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
> >> is similar to Earth.
>
> > I'm disappointed to find out a 'official' publication is relating the
> > atmosphere is near Earth like. I'm thinking it would need to be very,
> > very thick to support the flying reptiles, With Rider, as shown in the
> > film.
>
> Remember that the gravity is somewhat less than earth normal as well.
Yeah, but it's 80%, so instead of two hundred pounds the rider would
still be 160lbs.
berk
Phillip Thorne
>> According to the _Survival Guide_ (pp.6, 8), the specs are these:
>> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface pressure
>> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
>> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial pressure
>> is similar to Earth.
On Tue, 19 Jan 2010, "Mike Dworetsky"
<plati...@pants.btinternet.com> wrote:
>If the apparently abundant plant life is engaged in photosynthesis, and life
>has been evolving on Pandora for anything like as long as on Earth, I can't
>understand why CO2 would still be so high.
More immediately (it occurs to me looking at that number again), 18%
should cause an intense greenhouse effect. How low would Pandora's
insolation need to be to compensate? I can't find a reference for the
orbital radius of Polyphemus, the superjovian primary, within the
Alpha Centauri A system.
The book doesn't say, but ACA is a G2V star with 1.5 times the
luminosity of Sol.
<http://www.spaceref.com/news/viewpr.html?pid=11016>
>An equilibrium between O2, CO2, and organic carbon storage should
>exist ... What fraction of Pandora is covered by oceans?
"Although Pandora's land-to-water ratio is greater than Earth's, the
land is broken up into a larger number of smaller continents." (p.7)
That's not what the orbital view in the movie shows, or the photo on
p.4 -- the continents seem to be Earth-proportioned (not the only
inconsistency in the book). The book's illustrated mostly with
concept art, but if the production ever created a global map, it's not
included.
>If there is vulcanism, isn't there also going to be some (deadly)
>CO (carbon monoxide)?
Presumably, but the book doesn't mention it by name.
>The Xe is just plain weird. Xe is a rare element, while argon
>is very abundant in the cosmos.
Energetically favored during the "concentric shell" phase of stellar
nucleosynthesis? ISTR something like that.
The AlphaCent system is about the same age as our own; same
star-forming region, I suppose? You'd expect them to have similar
elemental compositions.
Phillip Thorne
>> According to the _Survival Guide_ (pp.6, 8), the specs are these:
On Tue, 19 Jan 2010, Andrew Plotkin <erky...@eblong.com> replied:
>Oh, well, if you're going include external information...
If we're going to conduct a discussion, we need specifics. And these
specifics just happen to be outside the movie. :)
(For comparison, where would Treknologists be without _The Starfleet
Technical Manual_, _Mr. Scott's Guide_, and _The ST:TNG TM_?)
>[...]
>Conclusion: reading the _Survival Guide_ doesn't help.
Well, not for *this* topic, but I haven't gotten to all the other
backstory reasons for why the place is so dangerous. Y'know, the ones
that the movie alleged but didn't demonstrate once it shifted mode and
mood.
Brian Davis
> One thing I would add though - 18% CO2 would likely induce rapid
> unconsciousness and death, not due to O2 starvation, but rather due to
> the way our bodies respond to elevated CO2 levels.
Agreed that 18% CO2 would be fatal (and has been, when it builds up in
caves under unusual circumstances). Xe, regardless of what webelements
implies, certainly has a biological activity - it turns out it's a
significant anesthetic (although not at Pandoran pXe).
The more interesting (OK, silly) question is what a reduced species
like H2S is doing in an atmosphere rich on O2... and what the heck can
produce Cl2 in the first place, let alone keep it in the air when
there's stuff like water around.
Then again... we're debating atmospheric chemistry of a fictional
planet with floating mountains.
--
Brian Davis
Mike Dworetsky
> Phillip Thorne wrote:
>>> According to the _Survival Guide_ (pp.6, 8), the specs are these:
>>> surface gravity 0.8 g, atmospheric density 1.2 Earth, surface
>>> pressure
>>> 1.1 Earth (i.e., ~1100 millibars), 18% CO2 (Earth: <0.1%), 5.5% Xe,
>>> H2S and Cl2 due to tidally-induced vulcanism. The O2 partial
>>> pressure is similar to Earth.
>
> On Tue, 19 Jan 2010, "Mike Dworetsky"
> <plati...@pants.btinternet.com> wrote:
>> If the apparently abundant plant life is engaged in photosynthesis,
>> and life has been evolving on Pandora for anything like as long as
>> on Earth, I can't understand why CO2 would still be so high.
>
> More immediately (it occurs to me looking at that number again), 18%
> should cause an intense greenhouse effect. How low would Pandora's
> insolation need to be to compensate? I can't find a reference for the
> orbital radius of Polyphemus, the superjovian primary, within the
> Alpha Centauri A system.
Depends on the insolation and orbit. Presumably some authorial handwaving
solves that one, though not the inconsistency of having lots of O2 and CO2
simultaneously.
>
> The book doesn't say, but ACA is a G2V star with 1.5 times the
> luminosity of Sol.
>
> <http://www.spaceref.com/news/viewpr.html?pid=11016>
>
>> An equilibrium between O2, CO2, and organic carbon storage should
>> exist ... What fraction of Pandora is covered by oceans?
>
> "Although Pandora's land-to-water ratio is greater than Earth's, the
> land is broken up into a larger number of smaller continents." (p.7)
>
> That's not what the orbital view in the movie shows, or the photo on
> p.4 -- the continents seem to be Earth-proportioned (not the only
> inconsistency in the book). The book's illustrated mostly with
> concept art, but if the production ever created a global map, it's not
> included.
>
>> If there is vulcanism, isn't there also going to be some (deadly)
>> CO (carbon monoxide)?
>
> Presumably, but the book doesn't mention it by name.
>
>> The Xe is just plain weird. Xe is a rare element, while argon
>> is very abundant in the cosmos.
>
> Energetically favored during the "concentric shell" phase of stellar
> nucleosynthesis? ISTR something like that.
This is authorial handwaving on a massive scale and ignores realities of
nucleosynthesis. Alpha Cen A is a main sequence star, and yes its
composition is similar to the Sun's. Argon, yes. Xenon, no, not at high
concentrations. The only stars known to be highly enriched in Xe are
Mercury-Manganese stars:
http://adsabs.harvard.edu/abs/2008MNRAS.385.1523D
(the abstract is free--a library sub is needed to see the article. Preprint
without final journal editing is at http://uk.arxiv.org/abs/0801.2485)
>
> The AlphaCent system is about the same age as our own; same
> star-forming region, I suppose? You'd expect them to have similar
> elemental compositions.
No, I doubt they came from the same star-forming event. The relative
velocity is too great for that.
Derek Lyons
>Then again... we're debating atmospheric chemistry of a fictional
>planet with floating mountains.
Which is, after all, pretty much an everyday activity around these
parts.
D.
--
Touch-twice life. Eat. Drink. Laugh.
http://derekl1963.livejournal.com/
-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
Brian Davis
>> Then again... we're debating atmospheric chemistry of a fictional
>> planet with floating mountains.
>
> Which is, after all, pretty much an everyday activity around these
> parts.
Well... usually, we worry about what the minimum number of assumptions
we have to swallow to "suspend disbelief". I really enjoyed the
movie... but I didn't even pretend to think there was science in it.
Here, for instance, the movie is violating so much basic chemistry the
average high school student should take notice.
OK, we also have fun poking holes in Star Trek, but come on, that's
not an intellectual exercise of rational thinking... it's pretty much
noting that some clown put his shoes on his hands and his gloves on
his feet, and is walking around loudly maintaining that it "makes
sense".
--
Brian Davis
Erik Max Francis
> The AlphaCent system is about the same age as our own; same
> star-forming region, I suppose? You'd expect them to have similar
> elemental compositions.
Alpha Centauri A is considerably older than the Sun, which is why its
luminosity is higher.
Even very nearby stars that actually are the same age as the Sun are
quite unlikely to have developed in the same stellar nursery as the Sun.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
We must use time as a tool, not as a crutch.
-- John F. Kennedy
Mike Van Pelt
Phillip Thorne <peth...@comcast.net> wrote:
>In the movie, all the human characters on Pandora wear rebreather
>packs (p.12) outside, because "You'll be unconscious in twenty
>seconds, dead in four minutes." But why, exactly?
It's easy to postulate an atmosphere that'd have this effect on
humans. It's slightly harder to come up with one which supports
life that can get along just fine in our atmosphere.
I think the 18% CO2 just by itself pretty much takes care of
that issue, though. I'm not fond of the H2S thing -- not
because it isn't toxic (it is) but because if there were lethal
amounts of H2S in Pandora's atmosphere, there should have been
numerous complaints by the human characters about the
all-pervasive rotten-egg stink from the little bit of it that
would cling to people's clothes as they came in and out of the
controlled atmosphere buildings.
--
Mike Van Pelt "If they're going to talk about
mvp.at.calweb.com Camelot, then we get to talk about
KE6BVH The Lady in the Lake." - ?
Tim Little
> I'm not fond of the H2S thing -- not because it isn't toxic (it is)
> but because if there were lethal amounts of H2S in Pandora's
> atmosphere, there should have been numerous complaints by the human
> characters about the all-pervasive rotten-egg stink from the little
> bit of it that would cling to people's clothes as they came in and
> out of the controlled atmosphere buildings.
Yes - most people can detect it at levels of about 10 parts per
billion. Like many odors, people accustomed to it may stop noticing
low levels of it, but rapid variations in concentration (such as
people coming in from outside) would still be detected. The gas
doesn't induce anosmia until 100 ppm, around the levels that are
lethal over long periods of time. It is also well above levels that
cause severe eye irritation, making it nearly impossible to see
clearly.
If Pandora had 0.1% H2S, it would be enough to kill a human with one
breath and even minor leakage around the edges of a respirator mask
would be very dangerous.
- Tim
Greg Goss
>The AlphaCent system is about the same age as our own; same
>star-forming region, I suppose? You'd expect them to have similar
>elemental compositions.
The system is the same age, but the planetary history is different.
Our planet was impacted by a mars-sized body early on, sending much of
the crust of both planets into our moon, and both cores into our
planet. In their case, an impacting body within the intense magnetic
field of Polyphemus caused different effects (including the creation
of large amounts of unobtainium with magnetic field lines pinned to
its crystal structure (rather than rejected).
Our impacting planet had essentially the same composition as anything
else in our system. Theirs could have been a rogue from elsewhere.
Or development in a gas giant system may have prevented dispersal of
gases from some primordial atmosphere when things line major impact
happen. Do we know what the trace elements on Titan are?
--
Tomorrow is today already.
Greg Goss, 1989-01-27
Erik Max Francis
> Phillip Thorne <peth...@comcast.net> wrote:
>
>> The AlphaCent system is about the same age as our own; same
>> star-forming region, I suppose? You'd expect them to have similar
>> elemental compositions.
>
> The system is the same age, but the planetary history is different.
No, the Alpha Centauri system is older.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
Eternity is very long, especially near the end.
-- Woody Allen
care...@gmail.com
H2S is about as toxic as hydrogen cyanide and kills as quickly, for
much the same reasons: they are both low molecular weight chemicals
that deactivate iron-containing enzymes essential for respiration.
I don't think 100 ppm is lethal over long periods of time, enzymes
exist that detoxify low level exposures so that less than about 250
ppm will never accumulate to lethal levels (again, this is like
cyanide). However, unlike cyanide, H2S has other toxic effects that
damage the organism with long term low-level exposure.
But the main problem with using H2S as a reason for Pandora's toxic
atmosphere is that plot points where someone loses his mask, passes
out (or nearly passes out) but then is revived by being given a mask
do not work. If you get a toxic exposure to H2S you are dead without
immediate specific invasive treatment to neutralize its effects.
Phillip Thorne
>Phillip Thorne wrote:
>> The AlphaCent system is about the same age as our own; same
>> star-forming region, I suppose? You'd expect them to have similar
>> elemental compositions.
>
>Alpha Centauri A is considerably older than the Sun, which is why its
>luminosity is higher.
The table in that Spaceref.com article cited 4850 My vs. 4650 My.
Apparently 200 My (2% of a G-class's lifetime) is a bigger difference
than I thought.
>Even very nearby stars that actually are the same age as the Sun are
>quite unlikely to have developed in the same stellar nursery as the Sun.
Hmmm, I hadn't thought of that. Okay, so if they're only temporarily
neighbors -- and probably not periodic neighbors, given what I expect
are chaotic effects during a 250 My galactic orbit -- then panspermia
between the two is unlikely.
Part of the "Avatar" background material claims Na'vi biochemistry
isn't DNA-based, which made creation of the recombinant avatars a
problem. But another part has xenobiologists speculating about
panspermia to Pandora after the K-T impactor. Oi. Get your
worldbuilding straight, Lightstorm.
Common biochemistry would make everything a lot more plausible, but
we'd have to assume panspermia from some third party.
Phillip Thorne
>One thing I would add though - 18% CO2 would likely induce rapid
>unconsciousness and death, not due to O2 starvation, but rather due to
>the way our bodies respond to elevated CO2 levels. Our bodies do not
This could explain something else in the movie: our atmospheric mix is
apparently unbreathable for the Na'vi. When the two avatars (Jake's
and Norm's) are activated, it's in an indoor lab, and the attending
human techs are wearing exopacks.
If the Na'vi have a CO2-based respiration-monitor like ours, but
calibrated to 18% CO2, then a Earthly *low* level could be problematic
for them.
If it were simply a matter of a toxin that the Na'vi can tolerate but
humans can't (H2S, SO2, spores, whatever), then an air mix minus the
toxin wouldn't bother them.
Erik Max Francis
> On Thu, 21 Jan 2010, Erik Max Francis <m...@alcyone.com> corrected:
>> Phillip Thorne wrote:
>>> The AlphaCent system is about the same age as our own; same
>>> star-forming region, I suppose? You'd expect them to have similar
>>> elemental compositions.
>> Alpha Centauri A is considerably older than the Sun, which is why its
>> luminosity is higher.
>
> The table in that Spaceref.com article cited 4850 My vs. 4650 My.
> Apparently 200 My (2% of a G-class's lifetime) is a bigger difference
> than I thought.
Well, depends on the source. Some put its age as high as about 6 Gyr,
about 20% longer than the Sun's.
>> Even very nearby stars that actually are the same age as the Sun are
>> quite unlikely to have developed in the same stellar nursery as the Sun.
>
> Hmmm, I hadn't thought of that. Okay, so if they're only temporarily
> neighbors -- and probably not periodic neighbors, given what I expect
> are chaotic effects during a 250 My galactic orbit -- then panspermia
> between the two is unlikely.
Stars escape their stellar nurseries shortly after birth and wander far,
far away. We have no idea, and probably no easy way of knowing, which
stars were born in the same nursery as the Sun. There's no reason to
think that nearby stars were among them. Indeed, there's plenty of
reason to think that they're nowhere near us, stellar lifetimes,
galactic distances, and galactic orbital periods being what they are.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
There's this perfect girl / Someone no one can see
-- Lamya
Mike Dworetsky
> On Thu, 21 Jan 2010, Erik Max Francis <m...@alcyone.com> corrected:
>> Phillip Thorne wrote:
>>> The AlphaCent system is about the same age as our own; same
>>> star-forming region, I suppose? You'd expect them to have similar
>>> elemental compositions.
>>
>> Alpha Centauri A is considerably older than the Sun, which is why its
>> luminosity is higher.
>
> The table in that Spaceref.com article cited 4850 My vs. 4650 My.
> Apparently 200 My (2% of a G-class's lifetime) is a bigger difference
> than I thought.
>
>> Even very nearby stars that actually are the same age as the Sun are
>> quite unlikely to have developed in the same stellar nursery as the
>> Sun.
>
> Hmmm, I hadn't thought of that. Okay, so if they're only temporarily
> neighbors -- and probably not periodic neighbors, given what I expect
> are chaotic effects during a 250 My galactic orbit -- then panspermia
> between the two is unlikely.
Radial velocity alone, -22.3 km/s, rules out any dynamical connection
between Sun and Alpha Cen. Also, the proper motion is 3.6 arcsec/yr
(transverse motion) which at a distance of 1.35 pc gives, um...transverse
V=23.0 km/s, so total space velocity relative to our system is 32.1 km/s.
>
> Part of the "Avatar" background material claims Na'vi biochemistry
> isn't DNA-based, which made creation of the recombinant avatars a
> problem. But another part has xenobiologists speculating about
> panspermia to Pandora after the K-T impactor. Oi. Get your
> worldbuilding straight, Lightstorm.
>
> Common biochemistry would make everything a lot more plausible, but
> we'd have to assume panspermia from some third party.
--