Part of The Electrochemistry of Comets by Dr. Franklin Anariba | Space News, posted on YouTube March 31, 2015
Please note, transcript is rough and may include some misinterpretations of certain words and terms.
What I’m going to do here is start to give you an illustration of what can happen actually in comets. So as you can see the title of my talk here is, Cometary-Electrochemistry. And actually, that’s the only thing that’s new here, the term. When you look at the literature, for instance, you see that astro-electrochemistry, there’s plenty of material there. Astro-electrochemistry means that a lot of the reactions that happen in space are driven by a potential difference. In addition, I came across a series of Russian scientists who actually proposed that electricity in the nucleus of comets can drive the deicing process of, say, water or methane. So those ideas are not new. What is new here is the idea that you have electrochemistry or electricity driving chemical reactions either in the nucleus of the comet or in the coma of the comet. That’s what is new, and that’s what I’m going to talk about.
And I figure that most of you don’t know who I am. So I just want to pinpoint the fact that I live in Singapore, I’ve been living and working there for four years, and I think some of you have been there before. So this is the outline of my talk, I’m going to be brief and simple, because the audience here is very diverse. I’ll tell you a little bit about what electrochemistry is, the composition of comets, and how the combination of these two concepts can actually provide us a framework of reactions happening in comets.
I will also mention the electrochemical model in question; the question about cyanide production and how that model can explain this, and I just make one prediction: if this
model is correct, then there is one observation we should see in the future.
So what is very interesting from a chemistry standpoint is that energy in a way, or electricity is kind of free in nature. This is a very good example here; and you probably know this. This is a zinc material, and here we have a copper. And once we connect these two, what happens is that electrons that are actually in the zinc will go in the direction of the copper. Now electrons flowing in a particular direction is electricity. This happens spontaneously. So nature actually gives us “free energy,” the energy you need depends on how you arrange these materials. So that’s the main concept here.
Now another concept I want to pinpoint here is this: In electrochemistry, if you have this particular cell which is a potential cell as a function of time, what’s going to happen is, the zinc material will actually dissolve. It gives us electrons, and at the same time dialectric coming from the atom, the atom becomes an ion. So on the negative side, in the negative region of the particular cell you get dissolution. And on the positive region here in the copper, you’re going to get an accumulation material. This material comes in because this copper here is a solution, a copper solution. Any other material will be attractive because in these regions you’re going to have extra electrons that will be attracted to it, it will capture those electrons, and the material will accumulate. So the key point here is that you have active electrodes, you’re going to have dissolution on the negative region, and you’re going to have accumulation of material on the positive region. That’s the key part of this slide.
Now energy, as I said before, is not just stored in metals; we can harness it. It’s not difficult to harness it. We actually do it all the time. An example of this is batteries. Batteries are energy. There is a store, and the only difference here is, how is it arranged?
Another concept that I want to introduce here on this slide is the idea of having inert electrodes. Here I show you active electrodes, actually the electrode itself dissolves and accumulates. And in this particular example here I say that you have electrodes which actually provide only the surface where the electrochemical reaction occurs. Good examples of this are carbon, gold, palladium, platinum, for instance, because there are no reactive materials. Now this going to come in handy when you think about the nucleus of a comet. A reaction is actually occurring in that particular case and location.
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.