Billede

Plasma kosmologi i laboratoriet
Det er et stort paradoks i komet videnskab : Vi får at vide, at en komet kerne er en kugle af is, eller en beskidt snebold , eller fnugget iset kugle, der akkumulerede for milliarder af år siden i solsystemets barndom. Kometer siges at sublimere is når de bevæger sig mod solen, og sol opvarmning er ansvarlig for meget komet aktivitet. Men denne argumentation efterlader utallige uforklarede spørgsmål i komet videnskab. Vi stiller spørgsmålet, kan videnskaben om elektrokemi give et svar på mange komet mysterier?


Det jeg har tænkt mig at gøre her, er at begynde at give dig en illustration af hvad der faktisk kan ske i kometer. Så som du kan se i titlen på min tale her handler det om; kometers - Elektrokemi. Og faktisk, er nyheden her, udtrykket. Når du ser på litteraturen, for eksempel i astro-elektrokemi, er der masser af materiale der. Astro-elektrokemi betyder, at en masse af de reaktioner, der sker i rummet er drevet af en potentiel forskel. Desuden faldt jeg over en række russiske forskere, som faktisk foreslår, at elektricitet i kernen af kometer kan drive afisnings processen med for eksempel vand eller metan. Så disse ideer er ikke nye. Hvad der er nyt her er den idé, at du har elektrokemi eller elektricitet der driver kemiske reaktioner enten i kernen af kometen eller i komaen af kometen. Det er, hvad der er nyt , og det er hvad jeg har tænkt mig at tale om.

Og jeg regner med, at de fleste af jer ikke ved hvem jeg er. Så jeg vil bare sige at jeg bor i Singapore, jeg har levet og arbejdet der i fire år, og jeg tror, ​​nogle af jer har været der før . Så dette er omridset af min tale, vil jeg gøre det kort og enkelt, fordi publikum her er meget forskelligartet. Jeg vil fortælle dig en lille smule om, hvad elektrokemi er, sammensætningen af ​​kometer, og hvordan kombinationen af ​​disse to begreber faktisk kan give os en konstruktion af reaktioner, som finder sted i kometer .

Jeg vil også nævne den pågældende elektrokemiske model; spørgsmålet om cyanid produktion, og hvordan denne model kan forklare dette, og jeg vil bare lave én forudsigelse: Hvis denne model er korrekt, så er der én observation, vi vil se i fremtiden.

Så hvad der er meget interessant fra et kemisk synspunkt er, at energi på en måde, eller elektricitet på en måde er frit i naturen. Dette er et meget godt eksempel; og du kender det sikkert godt. Dette er en zink materiale, og her har vi kobber. Og når vi forbinder disse to, hvad der sker, er at elektroner, som faktisk i zink vil gå i retning af kobber. Elektroner der strømmer i en bestemt retning er elektricitet. Dette sker spontant. Så naturen giver os faktisk " fri energi ", den energi du har brug for, afhænger af hvordan du arrangerer disse materialer. Så det er det vigtigste begreb her.

Et andet koncept jeg vil udpege her er dette: I elektrokemi, hvis du har denne særlige celle, som er en potentiel celle som en funktion af tiden, det der kommer til at ske, er at zink materialet rent faktisk vil opløses. Det giver os elektroner og som atomet bliver dilektrisk bliver atomet en ion. Så på den negative side, i det negative område af den særlige celle, får du opløsning. Og på den positive region, her i kobber, får du et akkumulativt ophobet materiale. Dette materiale kommer til fordi dette kobber her er en opløsning, en kobber-opløsning. Alle andre materialer vil være attraktive, fordi i disse regioner vil komme til at have ekstra elektroner, der vil blive tiltrukket af det, vil det fange de elektroner, og materialet vil akkumulere. Så det afgørende punkt her er, at du har aktive elektroder, du vil have opløsning på den negative region, og du kommer til at have ophobning af materiale på den positive region. Det er den centrale del af dette dias.

Som jeg nævnte tidliger bliver energi ikke bare oplagret i metaller, vi kan udnytte det. Det er ikke svært at tøjle det. Vi gør det faktisk hele tiden. Et eksempel vil være batterier. Batterier er energi. Der er oplagring og den eneste forskel er hvor det er arrangeret? Et andet koncept jeg gerne vil introducere her på dette dias er ideen om inaktive (inerte) elektroder, faktisk opløses og ophobes selve elektroden. Og i dette eksempel her, siger jeg at, vi har elektroder der kun dækker overfladen hvor den elektrokemiske reaktion sker. Gode ekspempler er kulstof, guld, palladium, platinum, for eksempel, fordi der ingen reaktive materialer er. Dette er behjælpeligt når man tænker på en komets kerne. Her har vi en reaktion på dette særlige sted.


Kommentar: Vi undskylder at resten af artiklen er på engelsk, men i vores bestræbelser på at få så meget information ud til vores danske læsere, så må vi af og til ty til blot delvis at oversætte artikler. Hvis du er interesseret i at hjælpe, så hører vi gerne fra dig: sott_da@sott.net


Now, I know that some of you know about electrochemistry; electrochemistry is a very difficult subject. So what I'm going to do here is tell you, what is the main concept of electrochemistry? It's very simple: you can have a reduction and oxidation reaction. Here's an example of an oxidation reaction, which occurs in the negatively charged region. And I'm doing this on purpose because the technology we use in electrochemistry is different from physicists and engineers, in terms of cathode and anode. So in the negatively charged region you have for instance an atom or iron atom, it gives off three electrons and you get an ion. Right? These electrons over here, if you're able to push them in a particular direction is what gives us a current. And the reduction will occur in the positively charged region. A good example here: two protons plus two electrons will give you hydrogen gas.

Now, this is the basics of electrochemistry; this is all I'm going to say about electrochemistry at this point. What I'm going to do now is talk about comets. What is the composition of comets? Well, now we know that comets are actually formed by several kinds of minerals. This is a good example over here, this is olivine, associated with volcanism and associated with high temperatures, and maybe with lightning. And these are just various forms of olivine, and what I will pinpoint to you is the fact that they are rich in transition metals. Transition metals are important in electrochemistry because either they provide a surface, or they provide electrons that are easy to reduce and oxidize. They have various oxidation states. Another point that I want to pinpoint here is that these are all silicates; silicate and oxygen are very abundant. Oxygen is a very electron-rich atom, which can also provide the electrons to provide current, provided you have a potential difference.

Another example is pigeonite, associated with Mars and moon meteorites. Again, very rich in iron. Cubanite, copper, iron and sulfur form in liquid water. This has been found in comets; this is very interesting because that means there is a very complex chemistry going on here. Other transition metals that have been found in the nuclei of comets are titanium, vanadium in the form of nitride, platinum, osmium, ruthenium, tungsten, and molybdenum, just to mention a few. So you can see it's very complex, the composition for electrochemistry is complex in comets.

In the coma of comets, this is several of the gases that have been identified: carbon monoxide, carbon dioxide, a series of oxides with nitrogen, sulfur oxides, hydroxyl, and I left out molecular oxygen and molecular nitrogen. So, you find all these compounds in comets. That will tell you already that this is very complex chemistry going on. In addition to that, you find organic molecules. Methane, cyanide, methanol, ethane, ethene, ammonia, carbonates. Again, the level of complexity is beginning to get higher, I would say. And, more complex organic molecules have been identified in comets. Aminoacetonitrile, for instance, acetic acid, amorphous carbon (you can think about charcoal), polycyclic aromatic hydrocarbons which are very important in agriculture for instance - people who work in agriculture always talk about Ph's, because they control basically the Ph of soil for instance - and surprisingly glycine, that is an amino acid.

So, how can this model work? I've talked about electrochemistry, I'm talking about the composition of comets. So how can we apply this electrochemical model? Here is a cartoon, and it's not up to scale as you can see. Here we have the Sun, here we have the solar wind which I will call the proton flux, because that is most of its composition even though we have some electrons in there. And here we have a nucleus, a dust tail, an ion plasma tail, and a coma.

This is what we see; this is the typical observation for comets. So what I'm proposing here is, this paradigm or this model can be true if we show that we have a potential difference. In this particular case, I'm making the sun the positive region because of the protons of the solar wind, and the nucleus will be the negative region. Now if you are able to show this, then you can apply without fear an electrochemical model. So this is the key part, and I think this is why it's going to take us a lot of time in the future, trying to show that there's a potential difference here. You can do it indirectly.

Now, in detail, how is this model going to work? Well, it will work in the following way? Here is an electrode, a negative region, which can be the nucleus, because it's rich in minerals, with silicates and transition metals. And here would be the solar wind which surrounds the nucleus as the comet approaches the Sun. Ok, so what we need to do here, like I said before, is to have a potential difference. If this is the case, this will drive any reaction. The key part here is, is that potential difference big enough to drive any potential that you want? We do this in the lab all the time. Now, this potential difference is going to create a current flow from the nucleus toward the positive region, which is the solar wind. While doing so, you're going to see the coma. Why? Because, what happens is you have this flow of electrons, electrons are going to collide with some of the electrons in these molecules, say for instance, carbon monoxide. So electrons that are being driven from the nucleus toward the positive region will go to the coma, collide with some of the gases, it's going to excite electrons from the C0 (carbon monoxide) to a higher energy state. When it decays down, it is going to give off energy. This energy is what see in terms of the visible range. So the intensity of the coma, and the color of the coma will depend on what kind of gas is being excited. So it depends on the abundance.

So what kind of reactions can we have on the nucleus, and it might be complex to some of you because this is chemistry. But I will keep it simple here. We know that Iron two plus, for instance, exists on these minerals. It's already an ion, but say you have a potential difference, (inaudible), this is possible, you can give off another electron, this electron means current. The same for manganese, and so on and so forth. You can even have manganese reaction with some of the water vapor, or gases that can be in a coma. You can have more complex structures, you can have solids, manganese oxide, for instance, and again you get current. Some of the silicate material that I showed you that are part of the mineral, can react with protons from the solar wind, and you can get some hydroxyls. The possibilities are endless. We don't really know exactly what's happening there. The point here is that you can get current and you can get material.

What happens on the positive side? On the positive side, I can envision only one type of reaction. And it is the formation of hydrogen gas. That's it. All right? So, in more detail, if we have a comet here (this is a cartoon), this model can actually explain the plasma formation of the coma, depending again on the abundance of all these gases, and maybe all the gases that I left out. So, for instance, if you have eighty percent cyanide abundance, you get one particular color and a particular intensity. If you have oxygen at a higher abundance of eighty percent, the color of the coma and the intensity of the coma is going to be different. Let me see if I can finish this up soon.

The plasma tail can be explained by the formation of irons. The plasma tail is mostly composed of irons, it can be explained here. In addition to that, the dust tail can be explained by the formation of these solids: oxides, hydroxides, in addition to that also some chunks of minerals. And most importantly here, when I started thinking about this particular model, I predicted the formation of hydrogen gas even before I read the literature, because I have no background on comets. And what we are able to see here which is very exciting is that with the Hale Bopp comet, for instance, a hydrogen cloud was actually observed, a very large hydrogen cloud. So this model explains that.

So how can we know there is an electrochemical process going on in comets? There was this particular observation a few years ago, cyanide formation and no dust formation. So what happened here is this: in the standard model, whenever you have sublimation of a gas, dust will always form, because the idea is that you have a dirty ball — a dirty "ice ball" - so sublimation of water will actually bring out the formation of the gas — or excuse me, of particles. In this case, we don't see that. So how can we explain this electrochemically? Two different ways. One way is the standard electrochemistry, where the reaction actually occurs on the nucleus. And I was able to see, for instance, and I'm rushing here because of time, I was able to see here that amines are actually the precursor for cyanide formation, provided you have acetic conditions. In the presence of protons in the solar wind, it makes it amenable, or viable. Here we have a methylamine, we have a glycine, a more complex amines - but as long as you have these structures there, in the coma or in the nucleus you can get cyanide. I'm going to keep this slide here, I'm going to mention really quick: this is a way that you can actually do experiments on the lab. You can actually have those gases in this container; here you have two electrodes, tungsten and stainless steel.

You apply a potential and you carry the reaction. When you have the reaction you apply electric field; you push it into mass spectrometer, and you can detect the product. And this work has been done already by Navarro-Gonzalez of National University of Mexico — he was trying to simulate reactions in the ionosphere of Titan - and that's what he did. And this is the 1997 work by C.N. Matthews, I think it was mentioned yesterday, this particular experiment will actually give you amino acids. But this particular experiment will also give you, if you have a combination of methane and ammonia, will also give you cyanide radicals. If you have a coronal discharge, and this has been done, this is experimental data, you will also get hydrocarbons and cyanide. Importantly, if you simulate lightning, nitrogen and methane, you also get hydrocarbons and cyanide. So there's two possibilities here. And I've got a few more slides, I think, to go. Here what I'm going to show you briefly is, you can have reversibility, between c0 and alcohols. C0 and alcohols and methane. So there's no direct connection between c0 and cyanide, which I was looking for. It's a two-step proces. You can have the reduction of c0 into methane, and this can be...maybe electrical discharge will form cyanide. It's two-step process. I didn't find one that works directly.

And so this is the last slide here. Bare with me, I've got seventeen minutes and I think I've got one minute left. This is a graph of voltage in this direction, and this is current here in this direction. If you start with voltage A — and I give you direction over here - if you have two electrodes and a solution, for instance, or you have gases, if you go from voltage A to voltage B, and you have chemicals in the system, you will be able to see some sort of reduction process here. So whatever chemical it is you will gain an electron or several of electrons. And you move it all the way to voltage B, and then if you reverse it, whatever compound you form here by the reduction process will be oxidized. And eventually you get to this point. And so here you have reduction oxidation, this is a typical [inaudible] process. Now how can this apply to comets? Well, this is the sun and here is the orbit of the comet. And this is direction of the comet. If you go in this direction, for instance, as the comet approaches the Sun, you should be able to see a reaction, whatever that reaction would be — it depends on the composition. As the comet departs the Sun, you should be able to see another type of reaction. If it is reversible, you should be able to see the reversibility here. But, OK, maybe it's not reversible. But you should be able to see a reaction here, and a reaction here. So this is the prediction that I make. And a good example here is: going between amino and cyanide. I don't know if NASA has made these observations, but this should be something that should occur.

All right, so this is the last slide here. Thank you for your time. What I'm saying here is, this is an illustration, this is still not a theory, this is just an illustration because I only had four weeks to work on this. But it seems to me that this electrochemical mode, provided that you have a voltage difference, can account for the hydrogen gas formation, the plasma in the coma, dust tail formation, and the ionized plasma that you see. And also any other reaction that doesn't involved dust formation. And this model can actually allow us to predict based on the reversibility of electrochemical systems, what will happen. Thank you for your time.