Why so? I have no clue what the appropriate probability should be -- I'm not even convinced it has any plausible physical meaning in this context. I just regarded it as an adjustable parameter and ran the calculation for Earth until the escape temperatures for H2 and He were below 300K and that for H2O above.
Yes, I've heard the argument that the Sun in its T-Tauri stage blew away all the light stuff from the inner planets. I'd be a weensy bit suprised if the 1/9 smaller potential amount of outgassing on Mars completely explains a 1/1000 smaller mass of atmosphere today. And how do we know there's no tectonics on Mars? It's got volcanoes and stuff. And what about the role of ingassing from comet impacts? Mars should get more of these, no?
Anyway, I'm not trying to express a serious opinion on where the Martian atmosphere went! I just wanted to see if a quick and dirty calculation could shed light on whether escape velocity could easily explain the difference.
Well...it was a back of the envelope calculation. There are many complicating factors I didn't take into account, from the nonuniformity of the temperature and density with altitude to the variations in solar illumination over the year, the effect of high-altitude photochemistry and so on.
But the point of a rough calculation is not to get definitive answers but just to get a basic idea of what's going on before you plunge into detailed calculations and complex models. It's a "common sense" check on the hall of mirrors you can get into with complex models and half-million lines of code calcualtions.
Do I think I can make firm predictions of which gas might have been lost and when? Nope. Do I believe, in general, the result that the lower escape velocity of Mars can't easily account for the difference in atmospheres? Yes.
Also, do I think the mean temperature is irrelevant? Not irrelevant, no. The nature of thermal equilibrium is such that all the other interesting temperatures on Mars (daily max, yearly max, max as a function of altitude, etc.) are all going to be related to the mean. So the mean is a rough general stand-in for any and all of them.
It has? I thought the consensus from the orbiters was that Mars has plenty of water. Frozen, to be sure. Or are you saying Mars may have a lot of water but it has a lot less than it started with? How do we know what it started with?
Re:For those who don't want to RTFA, the top 10:
on
10 Technologies MIA
·
· Score: 3, Funny
Hoo yah! I'm still using the same phone I bought in 1985 from Western Electric. This was not long after the break-up and they were still making 'em like they were going to lease 'em out to you and didn't want to have to come out and do repairs more often then every 25 years. It's built like a tank and has survived dozens of 6 foot dives to the kitchen floor. I'll probably be leaving it in my will to the grandkids.
Got the old-fashioned actual real bell on it, too, none of these namby-pamby tweedle-eedle-eep electronic imitations...harumph...
Now that is one interesting question, worthy of a back of the envelope calculation. Does the lower escape velocity of Mars (5 km/s) versus Earth (11 km/s) really doom Mars to far less atmosphere than the Earth?
If we integrate the Maxwell-Boltzmann probability distribution of the speed of gas molecules from the escape velocity of a planet to infinity, we get the fraction of gas molecules that at any instant are going faster than the escape velocity. Presumably if this fraction is higher than some limit, a limit determined by the net influx of gas from cosmic sources, e.g. microcomet impacts, then the planet will lose the gas, over geological timespans.
God knows what that limit is, but we might as well just run the calculation for Earth at a temperature of 300K and fiddle with the limit until we find the Earth losing its H2 and He but keeping H2O, the next heaviest gas, as well as N2, O2 and so forth. Then we can use the same limit with Mars' escape velocity to calculate the maximum surface temperature at which Mars can hold onto the various gases.
I'll append the code itself as a comment to my own post, but the results I get are these:
escape velocity = 5.00 km/s
log10(escape probability) = -50.0
gas -- max surface temp (K)
H2 -- 25.8
He -- 51.1
H2O -- 230.3
N2 -- 358.1
O2 -- 409.0
CO2 -- 562.5
The mean surface temperature of Mars is about 200K, so this crude calculation suggests keeping water is iffy, but nitrogen, oxygen and CO2 are probably there to stay.
On the other hand, the observation is that Mars has kept its water. Now, water is the lightest of the interesting common gases in Earth's atmosphere (N2, O2, H2O and CO2). That fact suggests Mars should have no more trouble holding onto a nitrogen/oxygen atmosphere than the Earth does.
I don't have a subscription to PNAS, so I could only read the abstract, but for what it's worth I think it goes like this:
All the evidence seems to be geochemical, e.g. they look at the chemical composition of rocks of a certain age and, knowing the chemical reactions that produce that composition, infer the chemical composition and temperature of the atmosphere at the time. This is not unlike the way the Mars Rovers are using the chemical composition of rocks on Mars to acquire evidence for or against the prior existence of liquid water.
They take for granted that everyone agrees there was a massive glaciation (the "snowball") at a certain time long in the past, and that the early atmosphere was reducing (high in methane, ammonia and water, low in oxygen and CO2), but underwent at another certain time, long in the past, and because of the evolution of photosynthetic organisms (the cyanobacteria), a fairly rapid change to an oxidizing system (high in free oxygen and CO2, low in methane and ammonia).
What they suggest is that the two events are not unconnected. By discarding certain evidence and adducing other, they argue the two events may be close in time. Hence there might be some connection.
The connection they suggest revolves around the facts that methane is a known powerful greenhouse gas, and the Sun was cooler in those days than it is now. I speculate they suggest the early Earth was unglaciated because large amounts of methane gave a strong greenhouse effect that compensated for the lower solar illumination.
But then the evil cyanobacteria (cue Imperial March music) evolved and started producing free oxygen like crazy, which reacted with the methane to produce water and CO2. Away goes the methane, away goes the greenhouse effect (since CO2 is less effective as a greenhouse gas than methane), and the Earth plunges into the deepfreeze.
Later, the Sun heats up a bit, so less greenhouse effect will keep the temps up, and also aerobic organisms start exhaling CO2 and farting a bit of methane, and all is once again serene.
The "close call" is because if the Earth were further from the Sun, like near the orbit of Mars, then there wouldn't be any replacement CO2 greenhouse effect, because the CO2 would just freeze out as dry ice.
Yeah, but the researchers must have some idea of how they plan to tackle those problem, or else why bother?
Well, I hazard they probably do have some ideas, but that they're vague speculation at best. The goal of creating organisms to live on Mars may be an ultimate goal, but I read their comments as saying they don't propose making that touchdown themselves -- they feel they're just moving the ball down the field a bit.
I thought it was always below freezing on Mars.
Oh no. It gets up to 60-70F or so. Well above freezing for most of the day in the lower latitudes, I believe.
[I]f the total barometric pressure is so low that liquid water always boils, how can even a plant built like the toughest cactus hope to exchange gases with the Martian atmosphere and not dry out?
Well, plants generally do actively dry in this way on Earth. That is, the liquid water they take in through the roots generally exits as vapor through the leaves, and often at quite a high rate. This isn't because of the low total pressure, but because the partial pressure of water in the atmosphere is often well below the vapor pressure of water. In other words, as long as the relative humidity is less than 100%, liquid water will evaporate from plants.
IIRC massive transpiration is actually necessary for tall trees to hoist nutrients via sap flow up to the crown. As the water evaporates out of the leaves it pulls the sap column up the tree.
Anyway, the key to not drying out is to take in as much liquid water via the roots as you're losing via the leaves. Hence the necessity for liquid water in growing plants on Mars. But a low atmospheric pressure, and a low vapor pressure of water, don't seem to mean much more than that transpiration is maybe faster than it might otherwise be.
Remarkably, there seem to be few to no Earth organisms that are capable of pulling water directly out of the air. Even the lichens and bacteria that live in the driest conditions seem usually to simply wait around until liquid water briefly appears and absorb that, then husband the stuff very carefully. There are supposedly some high-altitude lichens that might pull water directly from air, but this hasn't been fully confirmed as far as I know.
Limited proxy fighting, tense border "incidents", state-sponsored terrorism, and sneaky underhanded attempts to intimidate and destabilize the other regime were all routine aspects of the Cold War, too. The point is that, however icky these things are, they are not nearly as destructive as a full-scale general war.
I didn't say nuclear weapons would make Pakistan and India like each other or settle their differences in a warm and peaceful way, or that they would quit trying to viciously stab each other in the back every chance they get. I just said nukes have apparently made the two countries forswear the most violent option.
Re:When will we be rid of these pieces of junk.
on
Discovery Heading Home
·
· Score: 4, Insightful
Imagine if the investment made in these enormoud lemons, was put into improving and updating Apollo technology.
IIRC, Apollo was at the time seen by engineers as mostly a foolish PR-driven detour on the road to a sober and sensible aerospace vehicle, which would look a lot like -- the Space Shuttle! That is, the best general model of orbital access has always been considered to be some kind of rocketplane that would fly to space in controlled, gradually accelerating flight, and be piloted to a landing, and, of course, be re-usable. Hence Dyna-Soar, the X-15 project, and ultimately the Shuttle.
This whole Mercury-Gemini-Apollo interregnum in which monkeys and men were stuck in cans on top of modified ICBMs, the candle was lit, and everyone prayed while hanging on for dear life was widely considered the unfortunate result of an irrational sudden national urgency to get a man in space any way at all following the embarassment of Sputnik and Gagarin.
So, after we "won" the race to the Moon, the idea was that we should return to the unglamorous but sober business of building rocketplanes to orbit. Hence the Shuttle.
By the way, when you speak of "improving" Apollo technology, just what the heck do you have in mind? Updating the OS on the computers? Using composites in the crew capsule skin? Reshaping the windows to improve the view? See, any easily imaginable "improvements" are the merest cosmetic fluff that won't take us one step closer to the real Grail of spaceflight, which is cheap spaceflight.
After all, it's not hard for a major government to get a handful of national heroes to space every year. That isn't the issue at all. The problem is that, if space is ever to be anything more than a curiosity, it has to become easy and economical for your average firm to shoot up your average mid-level exec, a couple of average cubicle dwellers, and a few tons of hardware to support their mission, whatever it is. It's very hard to envision how going back to the Apollo model of 40 years ago is going to bring us significantly closer to that goal.
It was very difficult during the Second World War to actually hit what you were aiming at. Remember GIs dumped the bombs out of an airplane five vertical miles up while trying to avoid being shot out of the sky and, in the case of the British, at night. They rarely managed to hit their individual targets except accidentally.
Now, the great advantage of firebombs is that you don't really need to hit your target: the bombs start a huge firestorm and that takes care of things.
I expect in the early years the Allied command was sensitive to the horrors of indiscriminately bombing civilian areas, and fostered the flimsy comfort fantasy that the bombs were all being carefully aimed at military installations and factories. But by the end of the war they probably just gave this up as (1) laughably untrue and (2) unnecessary anyway, inasmuch as the American public in '44-'45 couldn't have cared less if every acre of Germany and Japan were blasted to fine ash. War is hell.
Well, to quote from the website to which you yourself pointed...
"In February of 1945, with the Russian army threatening the heart of Saxony, I was called upon to attack Dresden; this was considered a target of the first importance for the offensive on the Eastern front. Dresden had by this time become the main centre of communications for the defence of Germany on the southern half of the Eastern front and it was considered that a heavy air attack would disorganise these communications and also make Dresden useless as a controlling centre for the defence."
(Emphasis mine.) That's British Air Marshal Arthur Harris discussing why Dresden was bombed.
You may disagree with Harris about how important Dresden really was to the activities of the German Army, but there's little doubt that in general disrupting the enemy army's command and communication network is "instrumental to victory."
I think you look for short-period variations in the luminosity. These give you an upper limit on the size of the object, since the luminosity can't vary in a time less than it takes light to travel across the object.
Then you start considering ways to get an object of that (small) size putting out the observed amount of energy, and you find that only matter falling into a hole will do the trick.
The usual definition of "atrocity" in wartime is killing large number of people (1) who can't defend themselves and (2) without materially advancing your side's position in the war. Hence, the Third Reich's extermination of civilian Jews in Germany and Poland qualifies.
But the bombing of Dresden and Tokyo? First of all, these cities were perfectly capable of defending themselves (with anti-aircraft guns and fighters) and did so, which is why not all the bombers that went out came back. Secondly, there is no doubt firebombing enemy cities in general directly advanced the Allied cause by destroying the manufacturing base (not to mention the workers) of the enemy nation. That Dresden was less useful a military target than, say, Schweinfurt is a minor issue at best.
There is also the ancient tradition that you reap what you sow. The Allies did not begin the practise of indiscriminate aerial bombardment of civilians to terrorize national will. That honor belonged to the Axis powers, over London, throughout 1940. It seems a mite hypocritical to complain of the fact that they who sowed the wind reaped the whirlwind.
Ach, you sophomoric moral equivalence people are a giant pain in the arse. The important lesson of the outcome of the Second World War was that indelibly etched into all European and arguably East Asian peoples: Don't start global wars of conquest. Really bad things will happen to you if you do. This is a good thing, and helped keep the second half of the twentieth century from being nearly as bloody as the first (the intramural adventures of Stalin and Mao excepted).
No, I just neglected to mention I was restricting my observation to First World situations in which the relevant parties lived in the shadow of nuclear weapons. Perhaps I just naively supposed that would be obvious to the intelligent reader, and so no one would parachute in with true but irrelevant assertions that Martians were still murdering Neptunians wholesale in the outer planets, Staphylococci were still being persecuted as a species by antibiotic-wielding doctors the world over, and so forth.
The point of the OP was that the presence of nuclear weapons should increase the tendency of genocidal warfare wherever their influence is felt. My suggestion is that this is backward, their influence should decrease genocidal warfare tendencies. But neither of us has anything to say about situations where the influence of nuclear weapons is simply absent.
What you need to ask yourself is: what would have happened in Rwanda if the Hutus and Tutsis (or their superpower patrons, had they had any) had both had nukes. One side says: lots more carnage. The other says: on the contrary, they would have been forced to settle their differences some other (nonmilitary) way, because even dumfuks have understood since 1945 that, when everyone's spear is thermonuclear-tipped, there are no survivors on either side once the military switch is pulled.
I hardly think the Vietnam war qualifies as genocidal, by the way. The North Vietnamese and Viet Cong were targeted by the American military not for their racial origins but because they were waging war on South Vietnam.
Of course, when you include mere accidents like the radiation damage the Castle Bravo test inflicted on the Marshall Islanders and a fisherman or two, I begin to think your definition of "genocide" is so elastic it could accomodate nearly any random collection of human deaths. This seems fairly useless, unless of course it is not your intention in debate to confine yourself to rationality.
Well, this is silly:...if we used heavy enough elements, we could conceivably get them "xray hot". But by that point, we would very likely have reached the ultra-unstable elements that have only been created for very brief periods of time in the lab before decaying.
The lowest electronic energy level goes like Z, and X-rays start at about 100 eV. So you could easily get a soft X-ray out of something as small as oxygen or neon, which while not common are hardly the unstable transuranics you're talking about.
But the larger point is that a plasma, which is that of which an accretion disk is made, is perfectly capable of absorbing and emitting throughout the X-ray region. There's nothing strange about a plasma at 10^6 K, and it emits quite ordinary black body radiation with a peak in the X-ray.
So I think the parent was perfectly reasonable in saying the simplest way to think of this process in a general way is the conversion of gravitational potential energy to thermal energy (i.e. the kinetic energy of the the plasma) and then to radiation in the usual way.
I suspect any radiation produced by the direct gravitational acceleration due to the hole is miniscule. The acceleration required to keep a particle in an orbit of radius 10 km or so is trivial compared to the accelerations during an inelastic collision with another particle at (say) 60% of the speed of light.
Good God, quasars are anything but dark. They emit energy on the same scale as a galaxy. The only sense in which these were "dark" is that you couldn't see them in the visible spectrum from Earth. But as the article notes, their presence was inferred by X-ray radiation reaching us, and confirmed by IR radiation.
No, they don't need it. Photosynthesis relies on CO2 and water, so these two are an absolute must. Free oxygen is nice, because it allows oxidative respiration, by far the most efficient way to power your cell. But it isn't absolutely necessary: there are a variety of anaerobic respiration pathways used by organisms in various low-oxygen environments.
Presumably someone tailoring organisms to thrive on Mars could design in anaerobic respiration, because it exists down here already. But there is no way to design a carbon-based organism without a carbon source.
Well, you're certainly right about Africa. Africa holds genocides just about as often as Bono holds Feed Africa benefit megaconcerts. I hesitate to suggest any connection, however...
What I failed to make clear is that I was only talking about those regions and concerning those powers where there are nuclear weapons in play. Arguably there will be no more Treblinkas in part because the Israelis have the bomb.
I also don't get your point. What I said is that atomic weapons make armed conflict less likely, not more, and increase, not decrease, the civilian awareness of the cost of unrestrained genocidal warfare. How does the fact that Africans continue to hack each other to death with machetes (lacking nukes and often even machine guns) contradict this?
Indeed, wouldn't the sad list at the end of your hyperlink support my point? Africa is the one continent without atomic weapons (if we believe the South Africans), and it also seems to be the continent where violence is still seen as a pretty reasonable way to settle national-scale political conflicts. If merely preaching peace could stop people from waging war, wouldn't Africa be at least a little less violent nowadays? After umpty years of people preaching peace and love to the Africans, and sending them checks and Peace Corps volunteers to dig wells and address all those root causes of violence?
I'm just saying, review the bare facts: the First World bristles with nuclear instant megadeath. And the First World hasn't fought a national-scale war in two generations. In Africa people still have to kill each other relatively slowly, in a labor-intensive way, with knives and pointed sticks. And yet in Africa the tendency to kill each other at the national level (with knives and pointed sticks) hasn't changed in fifty years. Is this just some weird coincidence?
(1) The political leadership of the time were very sensitive to the argument that it was the acceptance of the negotiated surrender at the end of WWI that led directly to WWII. There was a strong feeling that because the "problem" of German militarism had not been solved in 1918 when the Allies (arguably) had the force to do it, it simply re-emerged in 1939 to swallow another generation of young men. Truman in particular was of this mind. He served on the Western Front in 1918, and he was dead-set against any repetition of the "failure" (as he saw it) of Versailles to solve the problem of Germany once and for all.
(2) The Soviets had suffered terribly at the hands of the Wehrmacht, and moreover had ambitions in Central Europe and the Far East that would be better realized with the ruination of Germany and Japan as cultures, let alone military powers. Stalin didn't give a damn about that (or any) staggering loss of life, if it meant he had a power vacuum to work with in Central Europe and in the Far East. And Truman felt he needed the Red Army.
(3) Very likely the only really important condition either the Germans or Japanese would have wanted was to surrender preferentially to the United States and greatly limit the post-war influence of the Soviets on them. Naturally Stalin was strongly opposed to that.
It's been said that the insistence on unconditional surrender was one of the true large mistakes of the American and British leadership, because it caused so much additional destruction to countries that were going to be our allies in the struggle against the Soviets. At the time, it was thought we needed the Soviets too much to threaten them with making separate peaces with the Axis powers. In hindsight, that seems to be a terrible decision, one that arguably condemned half of Europe to a further half-century of darkness before its true liberation.
Stalin may simply have played better geopolitical chess than anyone else.
You know, the opinion of even generals as to what would have happen if this decision instead of that were taken in a war is still the merest guesswork, and all too often wrong, sometimes disastrously so. That's why wars so rarely go the way they are planned. Indeed, it's why wars happen at all: how can a war commence unless the top military leadership of both sides believes it will win? Obviously one of them finds out, in due course, that it was terribly mistaken.
By contrast to theories, it's a historical fact that the bomb did end the war. The records of the Japanese cabinet are available, and there's no doubt that after Nagasaki the emperor intervened decisively on the side of those who wanted to end the war immediately.
It's fun and cool for people to speculate about how the war might have ended, had the bomb not brought it to an abrupt close, just like it's fascinating to speculate about what would have happened if Alexander hadn't died in Babylon, or how the Cuban Missile Crisis would have played out had Nixon won the election in 1960.
But, you know, when we listen to the theorists, we must bear in mind these are often the same class of people who predicted in August 1914 that the war in France would be over by Christmas, in 1942 that the Wehrmacht could roll over the Red Army like they had the Polish and French, in 1861 that that pesky rebellion in South Carolina could be suppressed in a few months, in 2003 that Hussein's crack troops would make Baghdad a bloodbath (and in 2004 that the insurgency was on its last legs) and so on and so forth.
I'm not saying military men are dumb or misguided. I'm just pointing out the plain fact that historically speaking very little is as inherently chaotic and unpredictable as the detailed course of a war.
My ignorant speculation is that I doubt the Japanese would ever have surrendered without an invasion, for the simple reason that no country has ever unconditionally surrendered to a mere economic blockade while it had effective armies in the field.
I also speculate that the American generals in the Pacific, particularly LeMay and MacArthur, looked askance on the bomb's use in later years (I don't think any of them strongly opposed its use at the time) because (1) They didn't much get along personally or politically with Truman, (2) The bomb made the hideous cost of the Okinawa campaign look foolish -- why spend 20,000 lives to capture a steppingstone to the home islands of Japan when there was to be no invasion? (3) The use of atomic bombs from the air instead of an invasion deprived them at the time and later of a great deal of high-level influence. Winning the war (or any subsequent major wars) became less a matter of mastering military science and more a matter of wiring up buttons to deliver gigantic brainless explosions. The essential decisions become more centered on the civilian leadership, reduced to when and where do we nuke. The role and accumulated wisdom of the experienced general becomes less relevant. (4) The bomb made a mockery of the military's traditional purpose of serving as a shield to the civilian population. With the bomb enemies could simply reach through each other's militaries and obliterate each other's civilian society. So what's the point of the army? What relevance is left to the brawny hero standing guard at the frontier?
This last is not a complete hypothetical. It was certainly noted more than once during the Cold War that the United States made a conscious decision to rely more on nukes for deterrence of the Soviets and less on a giant conventional military force. It was said we traded men and tanks, a larger military-industrial complex, a greater influence of the military on national policy, and possibly a peacetime draft for the ability of the civilian President to rain nuclear hellfire on our enemies at the touch of a button. How could this not reduce the importance, influence and morale of the generals?
Um, sorry. I wasn't trying to be impressive. I didn't solve the Schroedinger Equation for you or anything -- it's just high-school algebra.
I figure the bottom line is pretty transparent, no? The ultimate limit on an arcology illuminated by natural light is a couple of klicks on a side, with a few hundred million rooms. It's just mildly interesting to me that the answer is fairly small.
I thought/. was a site for nerds, anyway. What kind of nerd doesn't like math?? I must be getting old...
This line of thought might have been plausible in 1945, but history since that date has proven it spectacularly wrong.
In fact, the only large-scale genocides took place before the advent of nuclear weapons. In fact, since nuclear weapons were developed and used, and their terrible destructiveness has seeped into every rational and halfway rational mind on the planet, we have become more and not less sensitized to the ugly destruction of total national warfare, and, arguably, this is exactly why there have been fewer and fewer of these every year. You might like to think that lots of peace movements and moralizing fringe preachers have brought unprecedented peace to the world, but there's ample evidence for the contrary theory that we're all just, finally, scared enough of the consequences of full-scale war that we're routinely turning to other methods to solve our problems.
Why not consider India and Pakistan's conflict over the Kashmir as a case in point? We have strongly conflicting cultures (Hindu and Islamic), with a long history of oppressing the other when it is in minority status, and we have a bitter contest over a prize (the Kashmir), and we have stentorian nationalist leadership, dictatorial in the case of Pakistan, semi-dictatorial in the case of India earlier in this century.
Given this reality on the ground, the Indians and Pakistanis unsurprisingly fought three wars over the Kashmir in quick succession from the time of their formation as nations (1947) until 1971. Then both Pakistan and India decided to go nuclear, perhaps thinking foolishly (as people will) that this might give each an advantage over the other.
Now, your theory suggests that this should have led to a brutalisation of the Pakistani and Indian political culture, and increased willingness (say) to consider military options over peaceful. But what actually happened is that there's been no general war along this border for an unusually long 35 years, and it now seems the Pakistanis and Indians are realizing they will just have to uneasily get along, as the Soviets and Americans did during the Cold War, since each now has the capacity to obliterate the other.
So, whether or not The Bomb was good at ending World War II, it may well have had far more beneficial consequences in the decades following: by making World Wars III and IV and so forth simply unthinkable.
I think you're confusing basic research with late-stage technology. Your concerns are not trivial, but the fact that they haven't been addressed in the pre-alpha stage of the basic research isn't very important, or interesting.
They're at very early stages, here. They're just trying to stick extremophile bacteria genes in a plant to see if they can use these genes to tailor the plant's genome at all. You have to understand this is a pretty radical mixture of genes. You're trying to cross a soybean with a deep-sea bacterium, after all. They might as well be crossing a human with a redwood tree to improve the height of the former. If plants can be tailored in this way successfully, then the sky's the limit, and your problems are likely to be easily addressed.
Point 1, the only thing special about -20C is that pure free water is frozen, which is inconvenient for water-based life. But temperatures that fall well below freezing for substantial periods of time are hardly unique to Mars: just spend a winter in North Dakota or Siberia. Indeed, it is more the rule than the exception here on Earth that temps are well below freezing for substantial parts of the year. Nevertheless, plants thrive here. They just go dormant when the temperature is too low, and grow when the temperature rises. Temps on Mars are above freezing for plenty of hours in the year.
Point 2, you have to remember that what plants really care about in an atmosphere is CO2, because that's where they get the carbon atoms to build proteins and so forth. The Earth has an air pressure of 1000 millibars, but only 0.036% of that (0.4 millibars) is CO2. Mars has an air pressure of only 7-10 millibars, but that's almost all CO2. So from a plant's point of view, the air on Mars is actually richer than it is here.
Slashdot Mirror
...suggest something more like 10^-15 or 10^-20
Why so? I have no clue what the appropriate probability should be -- I'm not even convinced it has any plausible physical meaning in this context. I just regarded it as an adjustable parameter and ran the calculation for Earth until the escape temperatures for H2 and He were below 300K and that for H2O above.
Yes, I've heard the argument that the Sun in its T-Tauri stage blew away all the light stuff from the inner planets. I'd be a weensy bit suprised if the 1/9 smaller potential amount of outgassing on Mars completely explains a 1/1000 smaller mass of atmosphere today. And how do we know there's no tectonics on Mars? It's got volcanoes and stuff. And what about the role of ingassing from comet impacts? Mars should get more of these, no?
Anyway, I'm not trying to express a serious opinion on where the Martian atmosphere went! I just wanted to see if a quick and dirty calculation could shed light on whether escape velocity could easily explain the difference.
Well...it was a back of the envelope calculation. There are many complicating factors I didn't take into account, from the nonuniformity of the temperature and density with altitude to the variations in solar illumination over the year, the effect of high-altitude photochemistry and so on.
But the point of a rough calculation is not to get definitive answers but just to get a basic idea of what's going on before you plunge into detailed calculations and complex models. It's a "common sense" check on the hall of mirrors you can get into with complex models and half-million lines of code calcualtions.
Do I think I can make firm predictions of which gas might have been lost and when? Nope. Do I believe, in general, the result that the lower escape velocity of Mars can't easily account for the difference in atmospheres? Yes.
Also, do I think the mean temperature is irrelevant? Not irrelevant, no. The nature of thermal equilibrium is such that all the other interesting temperatures on Mars (daily max, yearly max, max as a function of altitude, etc.) are all going to be related to the mean. So the mean is a rough general stand-in for any and all of them.
It has? I thought the consensus from the orbiters was that Mars has plenty of water. Frozen, to be sure. Or are you saying Mars may have a lot of water but it has a lot less than it started with? How do we know what it started with?
Hoo yah! I'm still using the same phone I bought in 1985 from Western Electric. This was not long after the break-up and they were still making 'em like they were going to lease 'em out to you and didn't want to have to come out and do repairs more often then every 25 years. It's built like a tank and has survived dozens of 6 foot dives to the kitchen floor. I'll probably be leaving it in my will to the grandkids.
Got the old-fashioned actual real bell on it, too, none of these namby-pamby tweedle-eedle-eep electronic imitations...harumph...
Got to go take my medication now....
...because the text of a C program has "too many junk characters" and is "lame" by /. standards. Golly.
Now that is one interesting question, worthy of a back of the envelope calculation. Does the lower escape velocity of Mars (5 km/s) versus Earth (11 km/s) really doom Mars to far less atmosphere than the Earth?
If we integrate the Maxwell-Boltzmann probability distribution of the speed of gas molecules from the escape velocity of a planet to infinity, we get the fraction of gas molecules that at any instant are going faster than the escape velocity. Presumably if this fraction is higher than some limit, a limit determined by the net influx of gas from cosmic sources, e.g. microcomet impacts, then the planet will lose the gas, over geological timespans.
God knows what that limit is, but we might as well just run the calculation for Earth at a temperature of 300K and fiddle with the limit until we find the Earth losing its H2 and He but keeping H2O, the next heaviest gas, as well as N2, O2 and so forth. Then we can use the same limit with Mars' escape velocity to calculate the maximum surface temperature at which Mars can hold onto the various gases.
I'll append the code itself as a comment to my own post, but the results I get are these:
The mean surface temperature of Mars is about 200K, so this crude calculation suggests keeping water is iffy, but nitrogen, oxygen and CO2 are probably there to stay.
On the other hand, the observation is that Mars has kept its water. Now, water is the lightest of the interesting common gases in Earth's atmosphere (N2, O2, H2O and CO2). That fact suggests Mars should have no more trouble holding onto a nitrogen/oxygen atmosphere than the Earth does.
I don't have a subscription to PNAS, so I could only read the abstract, but for what it's worth I think it goes like this:
All the evidence seems to be geochemical, e.g. they look at the chemical composition of rocks of a certain age and, knowing the chemical reactions that produce that composition, infer the chemical composition and temperature of the atmosphere at the time. This is not unlike the way the Mars Rovers are using the chemical composition of rocks on Mars to acquire evidence for or against the prior existence of liquid water.
They take for granted that everyone agrees there was a massive glaciation (the "snowball") at a certain time long in the past, and that the early atmosphere was reducing (high in methane, ammonia and water, low in oxygen and CO2), but underwent at another certain time, long in the past, and because of the evolution of photosynthetic organisms (the cyanobacteria), a fairly rapid change to an oxidizing system (high in free oxygen and CO2, low in methane and ammonia).
What they suggest is that the two events are not unconnected. By discarding certain evidence and adducing other, they argue the two events may be close in time. Hence there might be some connection.
The connection they suggest revolves around the facts that methane is a known powerful greenhouse gas, and the Sun was cooler in those days than it is now. I speculate they suggest the early Earth was unglaciated because large amounts of methane gave a strong greenhouse effect that compensated for the lower solar illumination.
But then the evil cyanobacteria (cue Imperial March music) evolved and started producing free oxygen like crazy, which reacted with the methane to produce water and CO2. Away goes the methane, away goes the greenhouse effect (since CO2 is less effective as a greenhouse gas than methane), and the Earth plunges into the deepfreeze.
Later, the Sun heats up a bit, so less greenhouse effect will keep the temps up, and also aerobic organisms start exhaling CO2 and farting a bit of methane, and all is once again serene.
The "close call" is because if the Earth were further from the Sun, like near the orbit of Mars, then there wouldn't be any replacement CO2 greenhouse effect, because the CO2 would just freeze out as dry ice.
Yeah, but the researchers must have some idea of how they plan to tackle those problem, or else why bother?
Well, I hazard they probably do have some ideas, but that they're vague speculation at best. The goal of creating organisms to live on Mars may be an ultimate goal, but I read their comments as saying they don't propose making that touchdown themselves -- they feel they're just moving the ball down the field a bit.
I thought it was always below freezing on Mars.
Oh no. It gets up to 60-70F or so. Well above freezing for most of the day in the lower latitudes, I believe.
[I]f the total barometric pressure is so low that liquid water always boils, how can even a plant built like the toughest cactus hope to exchange gases with the Martian atmosphere and not dry out?
Well, plants generally do actively dry in this way on Earth. That is, the liquid water they take in through the roots generally exits as vapor through the leaves, and often at quite a high rate. This isn't because of the low total pressure, but because the partial pressure of water in the atmosphere is often well below the vapor pressure of water. In other words, as long as the relative humidity is less than 100%, liquid water will evaporate from plants.
IIRC massive transpiration is actually necessary for tall trees to hoist nutrients via sap flow up to the crown. As the water evaporates out of the leaves it pulls the sap column up the tree.
Anyway, the key to not drying out is to take in as much liquid water via the roots as you're losing via the leaves. Hence the necessity for liquid water in growing plants on Mars. But a low atmospheric pressure, and a low vapor pressure of water, don't seem to mean much more than that transpiration is maybe faster than it might otherwise be.
Remarkably, there seem to be few to no Earth organisms that are capable of pulling water directly out of the air. Even the lichens and bacteria that live in the driest conditions seem usually to simply wait around until liquid water briefly appears and absorb that, then husband the stuff very carefully. There are supposedly some high-altitude lichens that might pull water directly from air, but this hasn't been fully confirmed as far as I know.
Limited proxy fighting, tense border "incidents", state-sponsored terrorism, and sneaky underhanded attempts to intimidate and destabilize the other regime were all routine aspects of the Cold War, too. The point is that, however icky these things are, they are not nearly as destructive as a full-scale general war.
I didn't say nuclear weapons would make Pakistan and India like each other or settle their differences in a warm and peaceful way, or that they would quit trying to viciously stab each other in the back every chance they get. I just said nukes have apparently made the two countries forswear the most violent option.
Imagine if the investment made in these enormoud lemons, was put into improving and updating Apollo technology.
IIRC, Apollo was at the time seen by engineers as mostly a foolish PR-driven detour on the road to a sober and sensible aerospace vehicle, which would look a lot like -- the Space Shuttle! That is, the best general model of orbital access has always been considered to be some kind of rocketplane that would fly to space in controlled, gradually accelerating flight, and be piloted to a landing, and, of course, be re-usable. Hence Dyna-Soar, the X-15 project, and ultimately the Shuttle.
This whole Mercury-Gemini-Apollo interregnum in which monkeys and men were stuck in cans on top of modified ICBMs, the candle was lit, and everyone prayed while hanging on for dear life was widely considered the unfortunate result of an irrational sudden national urgency to get a man in space any way at all following the embarassment of Sputnik and Gagarin.
So, after we "won" the race to the Moon, the idea was that we should return to the unglamorous but sober business of building rocketplanes to orbit. Hence the Shuttle.
By the way, when you speak of "improving" Apollo technology, just what the heck do you have in mind? Updating the OS on the computers? Using composites in the crew capsule skin? Reshaping the windows to improve the view? See, any easily imaginable "improvements" are the merest cosmetic fluff that won't take us one step closer to the real Grail of spaceflight, which is cheap spaceflight.
After all, it's not hard for a major government to get a handful of national heroes to space every year. That isn't the issue at all. The problem is that, if space is ever to be anything more than a curiosity, it has to become easy and economical for your average firm to shoot up your average mid-level exec, a couple of average cubicle dwellers, and a few tons of hardware to support their mission, whatever it is. It's very hard to envision how going back to the Apollo model of 40 years ago is going to bring us significantly closer to that goal.
It was very difficult during the Second World War to actually hit what you were aiming at. Remember GIs dumped the bombs out of an airplane five vertical miles up while trying to avoid being shot out of the sky and, in the case of the British, at night. They rarely managed to hit their individual targets except accidentally.
Now, the great advantage of firebombs is that you don't really need to hit your target: the bombs start a huge firestorm and that takes care of things.
I expect in the early years the Allied command was sensitive to the horrors of indiscriminately bombing civilian areas, and fostered the flimsy comfort fantasy that the bombs were all being carefully aimed at military installations and factories. But by the end of the war they probably just gave this up as (1) laughably untrue and (2) unnecessary anyway, inasmuch as the American public in '44-'45 couldn't have cared less if every acre of Germany and Japan were blasted to fine ash. War is hell.
Well, to quote from the website to which you yourself pointed...
"In February of 1945, with the Russian army threatening the heart of Saxony, I was called upon to attack Dresden; this was considered a target of the first importance for the offensive on the Eastern front. Dresden had by this time become the main centre of communications for the defence of Germany on the southern half of the Eastern front and it was considered that a heavy air attack would disorganise these communications and also make Dresden useless as a controlling centre for the defence."
(Emphasis mine.) That's British Air Marshal Arthur Harris discussing why Dresden was bombed.
You may disagree with Harris about how important Dresden really was to the activities of the German Army, but there's little doubt that in general disrupting the enemy army's command and communication network is "instrumental to victory."
I think you look for short-period variations in the luminosity. These give you an upper limit on the size of the object, since the luminosity can't vary in a time less than it takes light to travel across the object.
Then you start considering ways to get an object of that (small) size putting out the observed amount of energy, and you find that only matter falling into a hole will do the trick.
The usual definition of "atrocity" in wartime is killing large number of people (1) who can't defend themselves and (2) without materially advancing your side's position in the war. Hence, the Third Reich's extermination of civilian Jews in Germany and Poland qualifies.
But the bombing of Dresden and Tokyo? First of all, these cities were perfectly capable of defending themselves (with anti-aircraft guns and fighters) and did so, which is why not all the bombers that went out came back. Secondly, there is no doubt firebombing enemy cities in general directly advanced the Allied cause by destroying the manufacturing base (not to mention the workers) of the enemy nation. That Dresden was less useful a military target than, say, Schweinfurt is a minor issue at best.
There is also the ancient tradition that you reap what you sow. The Allies did not begin the practise of indiscriminate aerial bombardment of civilians to terrorize national will. That honor belonged to the Axis powers, over London, throughout 1940. It seems a mite hypocritical to complain of the fact that they who sowed the wind reaped the whirlwind.
Ach, you sophomoric moral equivalence people are a giant pain in the arse. The important lesson of the outcome of the Second World War was that indelibly etched into all European and arguably East Asian peoples: Don't start global wars of conquest. Really bad things will happen to you if you do. This is a good thing, and helped keep the second half of the twentieth century from being nearly as bloody as the first (the intramural adventures of Stalin and Mao excepted).
No, I just neglected to mention I was restricting my observation to First World situations in which the relevant parties lived in the shadow of nuclear weapons. Perhaps I just naively supposed that would be obvious to the intelligent reader, and so no one would parachute in with true but irrelevant assertions that Martians were still murdering Neptunians wholesale in the outer planets, Staphylococci were still being persecuted as a species by antibiotic-wielding doctors the world over, and so forth.
The point of the OP was that the presence of nuclear weapons should increase the tendency of genocidal warfare wherever their influence is felt. My suggestion is that this is backward, their influence should decrease genocidal warfare tendencies. But neither of us has anything to say about situations where the influence of nuclear weapons is simply absent.
What you need to ask yourself is: what would have happened in Rwanda if the Hutus and Tutsis (or their superpower patrons, had they had any) had both had nukes. One side says: lots more carnage. The other says: on the contrary, they would have been forced to settle their differences some other (nonmilitary) way, because even dumfuks have understood since 1945 that, when everyone's spear is thermonuclear-tipped, there are no survivors on either side once the military switch is pulled.
I hardly think the Vietnam war qualifies as genocidal, by the way. The North Vietnamese and Viet Cong were targeted by the American military not for their racial origins but because they were waging war on South Vietnam.
Of course, when you include mere accidents like the radiation damage the Castle Bravo test inflicted on the Marshall Islanders and a fisherman or two, I begin to think your definition of "genocide" is so elastic it could accomodate nearly any random collection of human deaths. This seems fairly useless, unless of course it is not your intention in debate to confine yourself to rationality.
Well, this is silly: ...if we used heavy enough elements, we could conceivably get them "xray hot". But by that point, we would very likely have reached the ultra-unstable elements that have only been created for very brief periods of time in the lab before decaying.
The lowest electronic energy level goes like Z, and X-rays start at about 100 eV. So you could easily get a soft X-ray out of something as small as oxygen or neon, which while not common are hardly the unstable transuranics you're talking about.
But the larger point is that a plasma, which is that of which an accretion disk is made, is perfectly capable of absorbing and emitting throughout the X-ray region. There's nothing strange about a plasma at 10^6 K, and it emits quite ordinary black body radiation with a peak in the X-ray.
So I think the parent was perfectly reasonable in saying the simplest way to think of this process in a general way is the conversion of gravitational potential energy to thermal energy (i.e. the kinetic energy of the the plasma) and then to radiation in the usual way.
I suspect any radiation produced by the direct gravitational acceleration due to the hole is miniscule. The acceleration required to keep a particle in an orbit of radius 10 km or so is trivial compared to the accelerations during an inelastic collision with another particle at (say) 60% of the speed of light.
Good God, quasars are anything but dark. They emit energy on the same scale as a galaxy. The only sense in which these were "dark" is that you couldn't see them in the visible spectrum from Earth. But as the article notes, their presence was inferred by X-ray radiation reaching us, and confirmed by IR radiation.
No, they don't need it. Photosynthesis relies on CO2 and water, so these two are an absolute must. Free oxygen is nice, because it allows oxidative respiration, by far the most efficient way to power your cell. But it isn't absolutely necessary: there are a variety of anaerobic respiration pathways used by organisms in various low-oxygen environments.
Presumably someone tailoring organisms to thrive on Mars could design in anaerobic respiration, because it exists down here already. But there is no way to design a carbon-based organism without a carbon source.
Well, you're certainly right about Africa. Africa holds genocides just about as often as Bono holds Feed Africa benefit megaconcerts. I hesitate to suggest any connection, however...
What I failed to make clear is that I was only talking about those regions and concerning those powers where there are nuclear weapons in play. Arguably there will be no more Treblinkas in part because the Israelis have the bomb.
I also don't get your point. What I said is that atomic weapons make armed conflict less likely, not more, and increase, not decrease, the civilian awareness of the cost of unrestrained genocidal warfare. How does the fact that Africans continue to hack each other to death with machetes (lacking nukes and often even machine guns) contradict this?
Indeed, wouldn't the sad list at the end of your hyperlink support my point? Africa is the one continent without atomic weapons (if we believe the South Africans), and it also seems to be the continent where violence is still seen as a pretty reasonable way to settle national-scale political conflicts. If merely preaching peace could stop people from waging war, wouldn't Africa be at least a little less violent nowadays? After umpty years of people preaching peace and love to the Africans, and sending them checks and Peace Corps volunteers to dig wells and address all those root causes of violence?
I'm just saying, review the bare facts: the First World bristles with nuclear instant megadeath. And the First World hasn't fought a national-scale war in two generations. In Africa people still have to kill each other relatively slowly, in a labor-intensive way, with knives and pointed sticks. And yet in Africa the tendency to kill each other at the national level (with knives and pointed sticks) hasn't changed in fifty years. Is this just some weird coincidence?
I think the answer is in three parts:
(1) The political leadership of the time were very sensitive to the argument that it was the acceptance of the negotiated surrender at the end of WWI that led directly to WWII. There was a strong feeling that because the "problem" of German militarism had not been solved in 1918 when the Allies (arguably) had the force to do it, it simply re-emerged in 1939 to swallow another generation of young men. Truman in particular was of this mind. He served on the Western Front in 1918, and he was dead-set against any repetition of the "failure" (as he saw it) of Versailles to solve the problem of Germany once and for all.
(2) The Soviets had suffered terribly at the hands of the Wehrmacht, and moreover had ambitions in Central Europe and the Far East that would be better realized with the ruination of Germany and Japan as cultures, let alone military powers. Stalin didn't give a damn about that (or any) staggering loss of life, if it meant he had a power vacuum to work with in Central Europe and in the Far East. And Truman felt he needed the Red Army.
(3) Very likely the only really important condition either the Germans or Japanese would have wanted was to surrender preferentially to the United States and greatly limit the post-war influence of the Soviets on them. Naturally Stalin was strongly opposed to that.
It's been said that the insistence on unconditional surrender was one of the true large mistakes of the American and British leadership, because it caused so much additional destruction to countries that were going to be our allies in the struggle against the Soviets. At the time, it was thought we needed the Soviets too much to threaten them with making separate peaces with the Axis powers. In hindsight, that seems to be a terrible decision, one that arguably condemned half of Europe to a further half-century of darkness before its true liberation.
Stalin may simply have played better geopolitical chess than anyone else.
You know, the opinion of even generals as to what would have happen if this decision instead of that were taken in a war is still the merest guesswork, and all too often wrong, sometimes disastrously so. That's why wars so rarely go the way they are planned. Indeed, it's why wars happen at all: how can a war commence unless the top military leadership of both sides believes it will win? Obviously one of them finds out, in due course, that it was terribly mistaken.
By contrast to theories, it's a historical fact that the bomb did end the war. The records of the Japanese cabinet are available, and there's no doubt that after Nagasaki the emperor intervened decisively on the side of those who wanted to end the war immediately.
It's fun and cool for people to speculate about how the war might have ended, had the bomb not brought it to an abrupt close, just like it's fascinating to speculate about what would have happened if Alexander hadn't died in Babylon, or how the Cuban Missile Crisis would have played out had Nixon won the election in 1960.
But, you know, when we listen to the theorists, we must bear in mind these are often the same class of people who predicted in August 1914 that the war in France would be over by Christmas, in 1942 that the Wehrmacht could roll over the Red Army like they had the Polish and French, in 1861 that that pesky rebellion in South Carolina could be suppressed in a few months, in 2003 that Hussein's crack troops would make Baghdad a bloodbath (and in 2004 that the insurgency was on its last legs) and so on and so forth.
I'm not saying military men are dumb or misguided. I'm just pointing out the plain fact that historically speaking very little is as inherently chaotic and unpredictable as the detailed course of a war.
My ignorant speculation is that I doubt the Japanese would ever have surrendered without an invasion, for the simple reason that no country has ever unconditionally surrendered to a mere economic blockade while it had effective armies in the field.
I also speculate that the American generals in the Pacific, particularly LeMay and MacArthur, looked askance on the bomb's use in later years (I don't think any of them strongly opposed its use at the time) because (1) They didn't much get along personally or politically with Truman, (2) The bomb made the hideous cost of the Okinawa campaign look foolish -- why spend 20,000 lives to capture a steppingstone to the home islands of Japan when there was to be no invasion? (3) The use of atomic bombs from the air instead of an invasion deprived them at the time and later of a great deal of high-level influence. Winning the war (or any subsequent major wars) became less a matter of mastering military science and more a matter of wiring up buttons to deliver gigantic brainless explosions. The essential decisions become more centered on the civilian leadership, reduced to when and where do we nuke. The role and accumulated wisdom of the experienced general becomes less relevant. (4) The bomb made a mockery of the military's traditional purpose of serving as a shield to the civilian population. With the bomb enemies could simply reach through each other's militaries and obliterate each other's civilian society. So what's the point of the army? What relevance is left to the brawny hero standing guard at the frontier?
This last is not a complete hypothetical. It was certainly noted more than once during the Cold War that the United States made a conscious decision to rely more on nukes for deterrence of the Soviets and less on a giant conventional military force. It was said we traded men and tanks, a larger military-industrial complex, a greater influence of the military on national policy, and possibly a peacetime draft for the ability of the civilian President to rain nuclear hellfire on our enemies at the touch of a button. How could this not reduce the importance, influence and morale of the generals?
Um, sorry. I wasn't trying to be impressive. I didn't solve the Schroedinger Equation for you or anything -- it's just high-school algebra.
/. was a site for nerds, anyway. What kind of nerd doesn't like math?? I must be getting old...
I figure the bottom line is pretty transparent, no? The ultimate limit on an arcology illuminated by natural light is a couple of klicks on a side, with a few hundred million rooms. It's just mildly interesting to me that the answer is fairly small.
I thought
Well, they get extra points for striking first.
This line of thought might have been plausible in 1945, but history since that date has proven it spectacularly wrong.
In fact, the only large-scale genocides took place before the advent of nuclear weapons. In fact, since nuclear weapons were developed and used, and their terrible destructiveness has seeped into every rational and halfway rational mind on the planet, we have become more and not less sensitized to the ugly destruction of total national warfare, and, arguably, this is exactly why there have been fewer and fewer of these every year. You might like to think that lots of peace movements and moralizing fringe preachers have brought unprecedented peace to the world, but there's ample evidence for the contrary theory that we're all just, finally, scared enough of the consequences of full-scale war that we're routinely turning to other methods to solve our problems.
Why not consider India and Pakistan's conflict over the Kashmir as a case in point? We have strongly conflicting cultures (Hindu and Islamic), with a long history of oppressing the other when it is in minority status, and we have a bitter contest over a prize (the Kashmir), and we have stentorian nationalist leadership, dictatorial in the case of Pakistan, semi-dictatorial in the case of India earlier in this century.
Given this reality on the ground, the Indians and Pakistanis unsurprisingly fought three wars over the Kashmir in quick succession from the time of their formation as nations (1947) until 1971. Then both Pakistan and India decided to go nuclear, perhaps thinking foolishly (as people will) that this might give each an advantage over the other.
Now, your theory suggests that this should have led to a brutalisation of the Pakistani and Indian political culture, and increased willingness (say) to consider military options over peaceful. But what actually happened is that there's been no general war along this border for an unusually long 35 years, and it now seems the Pakistanis and Indians are realizing they will just have to uneasily get along, as the Soviets and Americans did during the Cold War, since each now has the capacity to obliterate the other.
So, whether or not The Bomb was good at ending World War II, it may well have had far more beneficial consequences in the decades following: by making World Wars III and IV and so forth simply unthinkable.
I think you're confusing basic research with late-stage technology. Your concerns are not trivial, but the fact that they haven't been addressed in the pre-alpha stage of the basic research isn't very important, or interesting.
They're at very early stages, here. They're just trying to stick extremophile bacteria genes in a plant to see if they can use these genes to tailor the plant's genome at all. You have to understand this is a pretty radical mixture of genes. You're trying to cross a soybean with a deep-sea bacterium, after all. They might as well be crossing a human with a redwood tree to improve the height of the former. If plants can be tailored in this way successfully, then the sky's the limit, and your problems are likely to be easily addressed.
Point 1, the only thing special about -20C is that pure free water is frozen, which is inconvenient for water-based life. But temperatures that fall well below freezing for substantial periods of time are hardly unique to Mars: just spend a winter in North Dakota or Siberia. Indeed, it is more the rule than the exception here on Earth that temps are well below freezing for substantial parts of the year. Nevertheless, plants thrive here. They just go dormant when the temperature is too low, and grow when the temperature rises. Temps on Mars are above freezing for plenty of hours in the year.
Point 2, you have to remember that what plants really care about in an atmosphere is CO2, because that's where they get the carbon atoms to build proteins and so forth. The Earth has an air pressure of 1000 millibars, but only 0.036% of that (0.4 millibars) is CO2. Mars has an air pressure of only 7-10 millibars, but that's almost all CO2. So from a plant's point of view, the air on Mars is actually richer than it is here.