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Old 24th April 2019, 12:43 AM   #1
HansMustermann
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But why is the rum... err... nitrogen gone?

So it occurred to me that all the "Venus was once like Earth" and "Mars was once like Earth" people are essentially wrong. Those never were ANYTHING like Earth. Namely, everything except Earth and Titan seems to be missing one thing almost entirely: Nitrogen.

Incidentally, this would also explain why Mars has such a thin atmosphere. Because it should be able to hold onto N2 just fine... if it had any to start with. As I was saying, Titan holds a thick atmosphere of N2 at lower gravity than Mars.

The problem with N2 vs O2 is one that doesn't even have anything to do with having a magnetic field. O2 is broken into atomic oxygen by just UV light from the sun, and then it either reacts with something or escapes into space. The same gravity that would allow you to hold onto O2, is nowhere near enough to hold the half weight of just O atoms. N2 is holding together much tighter, and needs higher frequency UV to break apart. The sun isn't producing very much of those frequencies, at its current temperature, and even less of it in the distant past when it was a cool young star.

This also ties in with the old terraforming thread, btw: yeah, well, just bringing water to Mars won't really cut it. We'd need to bring N2 from somewhere, ideally. And we have no real idea where.

This also has strong implications for life. We had some news recently about Phosphorous being rare in other nebulas. But Nitrogen is even more essential for anything even vaguely resembling life, as well as for holding onto your atmosphere, and down here having any seems to be an exception.

And I would say it has a pretty strong implication that Venus never was like Earth. We just never had nearly as much carbon in the atmosphere to start with, so I'm betting that Venus started its runaway greenhouse transformation long before Earth, and long before it could have any chance at a life that could give it an O2 atmosphere.

So anyway, this all gets me wondering: so where is all the Nitrogen? Just one planet and one moon in the whole solar system having any quantities worth talking about is making them rather an odd exception. What happened to N2 in other places? Or didn't they have any to start with? Probably didn't. But then where did WE get ours?
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Old 24th April 2019, 01:01 AM   #2
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Venus' atmosphere actually has 4 times as much Nitrogen by mass as Earth's. You can't just judge by percentages.

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Old 24th April 2019, 01:20 AM   #3
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Isn't terrestrial nitrogen largely of biological origin? Asking because I genuinely don't know.
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Old 24th April 2019, 01:28 AM   #4
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I believe it's Dissociated ammonia from the early atmosphere.

The vast majority of biological material is gained from the atmosphere to begin with!
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Old 24th April 2019, 04:05 AM   #5
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Hmm, well, ok, so I was wrong about Venus. Still, where's the N2 that Mars should have had, among other places?
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Old 24th April 2019, 04:14 AM   #6
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I'll just leave these here...


https://www.theodysseyonline.com/mar...nce-like-earth
"Mars, Venus and Earth are all terrestrial planets, relatively small in size and closest to the sun. At one point in history, they were all suspected to be similar in atmospheric composition, making it possible for them to support life. Over time, two of the planets slowly changed as they adapted to atmospheric and geologic processes, as well as orbital and rotational motions. The temperatures and composition of atmosphere of each planet contributes to the Goldilocks problem. Venus is too hot, Mars is too cold and Earth is just right. There are many factors that influenced two planets to spiral to polar opposites of the spectrum and one to stay the same."
"The three terrestrial planets all began the same way, but due to their characteristics in composition and distance, they all ended up at either opposite ends of the spectrum or right in the middle. There are thoughts that Earth could end up like Venus because of the increased carbon dioxide present in the atmosphere. What happened to Mars and Venus wasn’t an anthropogenic contribution."
https://www.space.com/5112-venus-mar...ilarities.html
"Both Venus's and Mars's atmospheres are about 95 percentcarbon dioxide. Earth's is mostly nitrogen now, but scientists think it used tobe more like the other rocky worlds."
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Old 24th April 2019, 04:22 AM   #7
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"According to the recent paper in Nature Geoscience: Nitrogen speciation in upper mantle fluids and the origin of Earth's nitrogen-rich atmosphere, N2 originates from regions of the Earth where plates are converging. Venus and Mars lack plate tectonics and therefore lack N2 in their atmospheres." -- https://earthscience.stackexchange.c...n-earths-atmos

There is some discussion at that link that suggests other reasons.

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Old 24th April 2019, 04:23 AM   #8
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Well, they've found nitrogen in the Martian dirt. Maybe it's all locked up in there?
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Old 24th April 2019, 04:29 AM   #9
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Triton and Pluto also have large quantities of nitrogen, it's just mostly solid.

Mars lost its nitrogen because it's too warm and too small to hold it for billions of years. Venus is practically as big as Earth. Most moons are also too warm and too small. Titan is the second largest moon in the solar system by a small margin, and is quite a bit colder than the largest (Ganymede). The Jovian moons also formed in the vicinity of Jupiter, which kept them even warmer when the solar system was forming.
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Old 24th April 2019, 06:41 AM   #10
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Originally Posted by cjameshuff View Post
Mars lost its nitrogen because it's too warm and too small to hold it for billions of years...
It also doesn't have a strong magnetic field protecting its upper atmosphere from being stripped away by the solar wind.
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Old 24th April 2019, 04:55 PM   #11
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Originally Posted by Jack by the hedge View Post
It also doesn't have a strong magnetic field protecting its upper atmosphere from being stripped away by the solar wind.
Neither does Venus, which additionally has about 4 times the intensity of solar wind. It's a factor, but not the main one. For the inner planets it mostly means they lost water more quickly than Earth through it getting cracked to hydrogen and oxygen, the hydrogen being lost very easily.
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Old 24th April 2019, 06:01 PM   #12
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Yeah, the solar wind is really good at helping get rid of hydrogen, but it hardly explains the loss of nitrogen.

Think of it this way: if it didn't get rid of all oxygen, which it didn't, N2 is MUCH heavier as a molecule than atomic oxygen is, after UV from the sun turned it atomic. At the same temperature, a lot more oxygen atoms will find themselves just above escape velocity than N2 molecules which aren't easily broken by almost anything that the sun puts out.
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Old 24th April 2019, 07:19 PM   #13
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HansMustermann

If I understand your argument correctly, you are saying that a large amount of nitrogen in the atmosphere is an indicator of life, and Earth has that, but Mars and Venus do not, and since nitrogen is the heaviest of the more common elements that would have been there, and therefore more difficult for the solar wind to strip away, so therefore, it should still be there if life had flourished there at one time.

Is that correct?
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Old 24th April 2019, 08:18 PM   #14
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Well, I'm not entirely sure how much you do need for life. Just that if you had a lot of it in the atmosphere, especially at the low temperatures of Mars, it would probably still be there.
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Old 24th April 2019, 08:44 PM   #15
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Why?

Quote:
However, early in its history Mars may have had conditions more conducive to retaining liquid water at the surface. In 2013, a team of scientists proposed that Mars once had "oxygen-rich" atmosphere billions of years ago.

Possible causes for the atmospheric escape of a previously thicker Martian atmosphere include:
- Gradual erosion of the atmosphere by solar wind. On 5 November 2015, NASA announced that data from MAVEN shows that the erosion of Mars' atmosphere increases significantly during solar storms. This shift took place between about 4.2 to 3.7 billion years ago, as the shielding effect of the global magnetic field was lost when the planet's internal dynamo cooled.
- Catastrophic collision by a body large enough to blow away a significant percentage of the atmosphere;
- Mars’ low gravity allowing the atmosphere to "blow off" into space by Jeans escape.
Atmosphere of Mars: Early atmosphere (Wikipedia)

Compared to:

Quote:
In October 2017, NASA scientists at the Marshall Space Flight Center and the Lunar and Planetary Institute in Houston announced their finding, based on studies of Moon magma samples retrieved by the Apollo missions, that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day Mars. It has been theorized, in fact, that this ancient atmosphere could have supported life, though no evidence of life has been found. The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space.
Ancient atmosphere of the Moon (Wikipedia)

ETA:
Quote:
Atmospheric escape is the loss of planetary atmospheric gases to outer space. A number of different mechanisms can be responsible for atmospheric escape, operating at different time scales; the most prominent is Jeans Escape, named after British astronomer Sir James Jeans, who described the process of atmospheric loss to the molecular kinetic energy. The relative importance of each loss process is a function of the planet's mass, its atmosphere composition, and its distance from its sun.
Atmospheric escape (Wikipedia)
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Old 24th April 2019, 08:55 PM   #16
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Originally Posted by Tolls View Post
Well, they've found nitrogen in the Martian dirt. Maybe it's all locked up in there?
NASA's Curiosity Rover Finds Biologically Useful Nitrogen on Mars

The equivalent of up to 1,100 parts per million nitrates in the Martian soil from the drill sites is indeed significant, especially if it is found deep too. Even on Earth geologic nitrogen doesn't typically reach those levels, ranging from ~80 ppm+/- in igneous rock to ~700 ppm+/- in fine sedimentary rock. And there are a few microbes that can extract enough mineral nitrogen from those levels in rock and make it bioavailable here on Earth. So I guess it really is potentially possible that bacteria could have released the excess Nitrogen obtained from mineral sources here on Earth, and potentially should we try to terraform Mars. NO2 is a greenhouse gas too. We know Mars has plenty of Oxygen locked in the minerals at the surface. That's why we call it the red planet. It's rusty with iron and oxygen.

The only thing I don't know how to calculate is how much N2 and NO2 would be available for atmosphere should seeded extremophile life start releasing it. However, I have been told we could get it to about about 120 mb O2 only due to Mars reduced gravity. That's marginal at best wearing a oxygen mask. Similar to Mt Everest "death zone", you couldn't survive long. And that's only after about 1000 years of terraforming.
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Old 24th April 2019, 11:27 PM   #17
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Just to make it clear, I'm not talking about oxygen. Oxygen is the third most abundant element in the universe. It's also very likely to end up combined with, well, just about most element, or blown into space.

There's an imperial buttload of oxygen on Mars -- e.g., in the silica or the iron oxide that makes it red -- and it's beyond doubt that it had a lot more. More likely as water, than an oxygen atmosphere, but still, it's clear that it had a lot.

I was asking about the nitrogen. You don't lose that one very easily.

Though I suppose that if the rock didn't reach high enough temperature during planet formation for the iron to sink to the core, it probably wasn't hot and fluid enough for the nitrogen to get out in the first place either.

Edit: to return to to smartcooky's message, though, if that's the case then we can probably lower our expectations of finding any signs of life. Aminoacids don't form in solid rock.
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Old 24th April 2019, 11:35 PM   #18
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Well, bacteria are a good bet, but bear in mind that they'd need to produce incredible quantities of the stuff. We're talking in the order of magnitude of 1018kg, or a billion billions kg. Well, a couple billion billions kg, if you want to walk around without a spacesuit. So you might have to let those bacteria work at it for a million years or so
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Old 25th April 2019, 03:57 AM   #19
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OK, so let me take a shot at this by looking at what might have happened on Venus.

Firstly, the atmosphere of Venus does actually have a lot of nitrogen. It makes up about 3˝%, which doesn't sound like much, until you take into account the fact that Venus' atmospheric density is about 100 times more massive than the Earth's, so the amount of nitrogen in the Venusian atmosphere is about four times greater. The problem is that Venus has a LOT of CO2

Most planetary scientists believe that Venus once had a similar atmosphere to that of the Earth. At some time in the past, the Earth's CO2 reacted with the planet's mantle and crust to form carbonates, which removed it from the atmosphere. AIUI, while some of the remainder dissolved in the oceans, the rest was turned into oxygen by cyanobacteria, and this is thought to have started taking place about 3 BYA

So, what happened on on Venus? Both planets seemed to have started out the same way; they both suffered the late heavy bombardment about 3.9 BYA that was thought to have delivered water to form planet wide oceans. The best guess is that Venus was too close to the sun, and therefore too hot for liquid water to remain on the surface. The water evaporated off into the atmosphere, Venus dried out, plate tectonics stopped and there was no mixture of crust and mantle, and once the crust became saturated with CO2, there were no oceans to soak up the remainder, so it went into the atmosphere, combined with the water vapour leading to the runaway greenhouse effect that turned it into the planetary hellhole it is today.

So now I come to Mars. It too may have had a similar atmosphere to Earth and Venus. It too would have suffered the late heavy bombardment. However, its problems went the other way. It was further from the sun, so it received less heating. It had much weaker gravity than the Earth or Venus (about 1/3) and, having cooled more quickly than the other two due its smaller size, the molten core solidified, causing its magnetic field to almost disappear. The solar wind and lower gravity combined to strip away its atmosphere, causing it to cool even more. Liquid water could no longer remain on it surface, so the water froze.

Its worth noting that the N : CO2 ratio in the atmospheres of Mars and Venus is about the same... its just that Venus' atmosphere is about 20,000 times more dense.

Its also worth noting that the atmosphere of Titan, which is about 1˝ times as dense as the Earth, is composed of 98.4% nitrogen, the remaining 1.6% is methane and hydrogen. Virtually no CO2 at all.
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Old 25th April 2019, 05:39 PM   #20
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Originally Posted by wollery View Post
I believe it's Dissociated ammonia from the early atmosphere.

The vast majority of biological material is gained from the atmosphere to begin with!
Fair enough.
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Old 25th April 2019, 08:25 PM   #21
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Originally Posted by smartcooky View Post
HansMustermann

If I understand your argument correctly, you are saying that a large amount of nitrogen in the atmosphere is an indicator of life, and Earth has that, but Mars and Venus do not, and since nitrogen is the heaviest of the more common elements that would have been there, and therefore more difficult for the solar wind to strip away, so therefore, it should still be there if life had flourished there at one time.

Is that correct?
I think he's just saying that if Mars or Venus had had a similar amount of nitrogen to earth, it would still be there. It isn't, therefore it wasn't there originally. This shows that both Mars and Venus were different from Earth in this rather significant way even early in the history of the solar system.


This sentence in the OP does suggest a little more though:
Quote:
But Nitrogen is even more essential for anything even vaguely resembling life, as well as for holding onto your atmosphere, and down here having any seems to be an exception.
There seems to be a further suggestion from this (but I'm not clear here) that the nitrogen in the atmosphere might protect the oxygen from being atomised and lost to space by absorbing some of the solar radiation. At least, I think that was the idea.

Maybe he's just saying that with nitrogen in the atmosphere the total atmosphere would be thicker, not that the total amount of oxygen or other gasses not including nitrogen, would be greater.

ETA It seems that other posters, including yourself, have noted that Venus' atmosphere isn't actually low in nitrogen as compared to the Earth.
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Old 26th April 2019, 01:47 AM   #22
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As I was saying, I may have been wrong about Venus. I know it may come as a shock to everyone, but I'm not infallible like the pope

But I'm still seriously doubting we'll find ancient life on Mars.
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Old 26th April 2019, 01:50 AM   #23
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I think that if we do, it'll probably be of the same kind as Earth life. Ie, cross contamination of some kind. I think that's probably going to be the explanation if we find life under the ice on Europa. I think that we'll need to go to another star to get life that is genuinely different.
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Old 26th April 2019, 04:38 AM   #24
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Originally Posted by HansMustermann View Post
As I was saying, I may have been wrong about Venus. I know it may come as a shock to everyone, but I'm not infallible like the pope

But I'm still seriously doubting we'll find ancient life on Mars.
So you're hinting maybe we should ask the pope about life on Mars?
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Old 26th April 2019, 06:17 AM   #25
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Perhaps Mars lacks nitrogen in its atmosphere - cf Earth and Venus - but has lots of CO2 because enough N2 can escape from the upper atmosphere (high energy end of the Maxwell-Boltzmann distribution) but CO2 can't?

Yeah, better to phrase this as something like mean depletion time (sorta the mean time for half the mass to escape), so ~millions of years (Mars) vs ~billions (Earth, Venus) for N2, ~trillions for CO2, but you get the idea.

Open question: why hasn't the solar wind - especially during times with lots of CMEs - "eroded" the Venusian atmosphere, over geologic timeframes?
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Old 26th April 2019, 06:35 PM   #26
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Originally Posted by smartcooky View Post
Its also worth noting that the atmosphere of Titan, which is about 1˝ times as dense as the Earth, is composed of 98.4% nitrogen, the remaining 1.6% is methane and hydrogen. Virtually no CO2 at all.
It's also worth noting that the temperature on Titan is 93.7 K, well below the coldest temperatures on Mars, where CO2 seasonally freezes out at the poles at much lower pressures. CO2 is mostly a solid on Titan.
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Old 26th April 2019, 06:40 PM   #27
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Originally Posted by JeanTate View Post
Perhaps Mars lacks nitrogen in its atmosphere - cf Earth and Venus - but has lots of CO2 because enough N2 can escape from the upper atmosphere (high energy end of the Maxwell-Boltzmann distribution) but CO2 can't?

Yeah, better to phrase this as something like mean depletion time (sorta the mean time for half the mass to escape), so ~millions of years (Mars) vs ~billions (Earth, Venus) for N2, ~trillions for CO2, but you get the idea.

Open question: why hasn't the solar wind - especially during times with lots of CMEs - "eroded" the Venusian atmosphere, over geologic timeframes?
It has. Normal hydrogen is lost faster than deuterium, which has double the atomic mass. The D/H ratio of the atmosphere of Venus is 100 times higher than that of Earth.
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