What do we need for life?

One question that intrigues man people is, is there life in the Universe besides what we see? Logic would say, almost certainly yes. The reason is we know there is a non-zero probability that it can form elswhere because it did here. That probability may be small but there is an enormous number of stars in the Universe (something in excess of 10^22 that we can see) that the conditions that led to life here must be reproduced a very large number of times. Of course, while there are such a large number of stars, by far the most are at such an extraordinarily large distance from us that they are essentially irrelevant. For the bulk of them, it took the light more than ten billion years to get here. But if we were to look for life nearby, where would we look? To answer that, we need to ask ourselves, what conditions are needed to get life started? The issue is NOT where can life exist, but rather where can it form. We know life can be found now on Earth in a wide range of environments, but that does not mean it can form there. It can migrate from somewhere else, gradually evolving systems needed to stabilize it to the new environment. The most obvious example is life emerging from the water to live on land. Nobody suggests life did not start in water because you need a solution to move nutrients around.

The first question to ask is, what are the most difficult things to achieve for life to get started? I think the four hardest things to get started are reproduction, energy transport, solubilization, and catalysis. Catalysis is required to make the chemical reactions that are desirable to go faster, and thus get more of the available resources going in the desired direction. (In this, when I use the word “desired” I mean to get on a right track to where life can get going and then support that choice during subsequent evolution. I do not mean to imply some sort of planning or directing.) Solubilization is required because many of the chemicals with functions that will be needed are not soluble in water, and hence they would simply settle out as a layer of brown gunk, which, as an aside, is what happens in many experiments designed to simulate the origin of life. What needs to happen is that something joins on at a place that does not spoil the function and then conveys solubility. Energy transport is a critical problem: if you do not have something that stores energy, functionality is restricted to microdistances from energy inputs.

Each of these critical functions, as well as reproduction, as I shall show below, depend on forming phosphate esters. Thus energy transport is mediated by adenosine tripolyphosphate (ATP), solubilisation of many of the most primitive cofactors that do not contain a lot of nitrogen or hydroxyl groups is aided by an attached adenosine monophosphate (AMP), initial catalysts came from ribozymes, RNA would be the initial source of reproduction, and both ribozymes and RNA (the latter is effectively just far longer strands of the former) are both constructed of AMP or the equivalent with different nucleobases. The commonality is the ribose and phosphate ester.

Catalysis is an interesting problem. Currently, enzymes are used, but life could not have started that way. The reason lies in the complexity of enzymes. The enzyme that will digest other protein, and hence make chemicals available from failed attempts at guessing the structure of a useful enzyme, has a precise sequence of three hundred and fifteen amino acids. There are twenty different common amino acids used (and in abiogenic situations, a lot more available) and these occur in D- and L- configurations, except for glycine, which means the probability of getting this enzyme is two in 39^315. That number is incredibly improbable. It makes selecting a specific proton in the entire Universe trivial in comparison. Worse, that catalyses ONE reaction only. That is not how initial catalysis happened.

Now, look at the problem of reproduction. Once a polymer is formed that can generate some of whatever requirements life needs, if it cannot copy itself, then it is a one-off wonder, and eventually it will degrade and be lost without a trace. Reproduction involves the need to transfer information, which in this case is some sort of a pattern. The problem here is the transfer must be accurate, but not too accurate initially, and we need different entities. By that I mean, if you just reproduced the same entity, such as in polyethene, you have two units of information: what it is and how long it is, but that second one is rather useless because life has no way of measuring the length without having a very large set of reference molecules. What life here chose appears to have been RNA, at least to start with. RNA has two purines and two pyrimidines, and it pairs them in a double helix. When reproduction occurs, one strand is the negative of the other, but if the negative pairs, we now have two strands that are equivalent to each original strand. (you retain the original.) There are four variations possible from the canonical units at any given position, and once you have many millions of units, a lot of information can be coded.

Why ribonucleic acid? The requirement is to be able to transfer information reliably, but not too accurately (I shall explain why not in a later post.) To do that, the polymer strands have to bind, and this occurs through what we call hydrogen bonds, which each give a binding energy of about 13 kJ/mol. These are chosen because they are weak enough to be ruptured, but strong enough you can get preferences. Thus adenine binds with uracil through two hydrogen bonds, which generates a little over 26 kJ/mol. (For comparison, a carbon-carbon bond is about 360 kJ/mol.) To get the 26 kJ/mol. the two hydrogen bonds have to be formed, and that can only happen of the entities have the right groups in the correct rigid configuration. When guanine bonds with cytosine, three such hydrogen bonds are formed, and the attraction is just under 40 kJ/mol. Guanine can also bind with uracil generating 26 kJ/mol., so information transfer is not necessarily totally accurate.

This binding through hydrogen bonds is critical. The bonding is strong enough to give a significant preference for each mer, but once the polymer gets long enough, the total energy (the sum of the energy of the individual pairs) holding the strands together gets to be those energies above multiplied by the number of pairs. If you have a million pairs, the strength of diamond becomes trivial, yet to reproduce, the strands must be separated. Hydrogen bonds can be separated because as the strands start to separate, water also hydrogen bonds and thus makes up for the linking energy. However, that alone is insufficient because the strand itself would be insoluble in water, and if so, the two strands linked together would remain insoluble (for those who know what this means, entropy strongly favours keeping the strands together). To achieve this, we need something that joins the mers into a chain, adds solubility, forms stable chemical bonds in general but is equally capable of being broken so that if the information creates something that is useless, we can recycle the chemicals. Only phosphate fills these requirements, but phosphate does not bind nucleobases together. Something intermediate is required, and that something is ribose.

In the next posts on this topic, I shall show you where this leads in seeing where life might be.

Advertisements

Asteroid (101955) Bennu

The results of the OSIRIS-REx probe have now started to be made public, and while this probe was launched to answer questions about carbonaceous asteroids, and while some information has been obtained that is most certainly interesting, what it has mainly done, in my opinion, is to raise more questions. As is often the case with scientific experiments and observations.

Bennu is a carbonaceous asteroid with a semimajor axis of about 1.26 AU, where 1 AU is the Earth-Sun distance. Its eccentricity is 0.2, which means it is Earth-crossing and could collide with Earth. According to Wikipedia, it has a 1 in 2700 chance of impacting Earth between 2175 – 2199. I guess I shall never know, but it would be a threat. It has a diameter of approximately 500 meters, and a mass of somewhere in the vicinity of 7 x 10^10 kg, which means an impact would be extremely damaging near where it struck, but it would not be an extinction event. (The Chicxulub impactor would have been between five to seven orders of magnitude bigger.) So, what do we know about it?

It is described as a rubble pile, although what that means varies in terms of who says it. It is generally not considered to be an original accretion, and it is usually assumed to have formed inside a much larger planetoid which provided heat and pressure to form more complex minerals. Exactly why they are so sure of this is a puzzle to me, because we do not know what the minerals are, and how they are bound into the asteroid. Carbonaceous asteroids usually are found in the outer asteroid belt, and the assumption is this was dislodged inwards as a result of the collision that formed it. Standard theory assumes there were such collisions, but it also assumes such collisions led to planetary formation, and the rather awkward fact that there are no planets in the asteroid belt tends to be overlooked. These collisions are doing a lot of work, first making protoplanets then planets, and second, smashing up protoplanets to make asteroids, with no explanation why two different results arise other than “we need two different results”. Note that the collision velocities in the asteroid belt would be much milder than for the rocky planets, so smashing is more likely the closer to the star. Its relevance to planetary formation may be low since it did not form a planet, and there are no planets that have compositions that could realistically be considered to have come from such a chemical composition.

It is often said that Earth was bombarded with carbonaceous chondrites early on, and that is where the reduced carbon and nitrogen came from to sustain life, as well as the amino acids and nucleobases used to create life. Additionally, it is asserted that the iron and a number of other metals that dissolve in iron that we have on the surface must have come from asteroids, the reason being that in the early formation of Earth, the whole was a mass of boiling silicates in which such metals would dissolve in iron and go to the core. That we have them means something else must have brought them later. This shows one of the major faults of science, in my opinion. Rather than take the observation as a reason to go back and question whether the boiling silicates might be wrong, they introduce a further variable. Unfortunately, this “late veneer”  is misleading because the advocates have refused to accept that we have fragments of asteroids as meteorites. Their isotopes show they could only have contributed the right amount of metals, etc, if they were emulsified in all of Earth’s silicates. But wait. Why would these be emulsified and not go to the core while the original metals were not emulsified and did go to the core?

These asteroids are also believed by many to be the origin of life. They have very small amounts of amino acids and nucleobases, but they have a much wider range of amino acids than are used by our life. If they were the source, why did we not use them? Even more convincing, the nitrogen in the meteorite fragments has more 15N than Earth’s nitrogen. Ours is of solar composition; the asteroids apparently processed it. There is no way to reduce the level of heavy isotopes so these asteroids cannot be the source.

Now, what does a rubble pile conjure up in your mind? I originally considered it to be, well, a pile of rubble, loosely adhering, but Bennu cannot be that. First, consider the escape velocity, which is more than 20 cm/sec in the polar regions but reduces down to 10 cm/sec at the equator, due to the centrifugal force of its rotation. That is not much, and anything loose would be lost in any impact. Yet the surface is littered with boulders, three more than 40 m long. Any significant shock would seemingly dislodge such boulders, especially smaller ones, but there they are, some half buried. There are also impact craters, some up to 150 meters in diameter. Whatever hit it to create that and excavate a hole 150 m in diameter must have delivered a shock wave that should impart more than 10 cm s−1 to a loosely lying boulder, although there is one possible exception, which is when the whole structure was sufficiently flexible to give without fragmenting and absorb the energy by converting it to heat while adding to the kinetic energy of the whole.

Which brings us back to the rubble pile. Bennu’s relative density is 1.19, so if placed in water it would not float, but it would not sink very quickly either. For comparison, it is less than half that of granite and about a third of many basalts. CI asteroidal material has a bulk density of 1.57, while CM asteroidal material has a bulk density of 2.2.  Accordingly, it is concluded that Bennu has a lot of voids in it, which is where the concept of the rubble pile comes to bear. On the other hand, there is considerable stiffness, so something is restricting movement.

So what do we not know about this asteroid? First, we have only a modest idea of what it is made of, although a sample return might be possible. It may well be made entirely of large boulders plus the obvious voids put together with something sticking the boulders together, but what is the something? If made of boulders, what are the boulders made of? It never got hot enough out there to melt silicates, so whatever they are must b held together by some agent, but what? How resilient is that something, and how many times can it be used before it fails? This is important in case we decide it would be desirable to alter its orbit to avoid a collision with Earth. What holds the boulders together? This is important if we want to know how planets form, and whether such an asteroid will be useful in any way. (If, for example, we were to build a giant space station, the nitrogen, organic material and water in such an asteroid would be invaluable.) More to do to unravel this mystery.

Some Shortcomings of Science

In a previous post, in reference to the blog repost, I stated I would show some of the short-comings of science, so here goes.

One of the obvious failings is that people seem happy to ignore what should convince them. The first sign I saw of this type of problem was in my very early years as a scientist. Sir Richard Doll produced a report that convincingly (at least to me) linked smoking to cancer. Out came a number of papers rubbishing this, largely from people employed by the tobacco industry. Here we have a clear conflict, and while it is ethically correct to show that some hypothesis is wrong, it should be based on sound logic. Now I believe that there are usually a very few results, and maybe as few as one specific result, that makes the conclusion unassailable. In this case, chemists isolated the constituents of cigarette smoke and found over 200 suspected carcinogens, and trials with some of these on lab rats were conclusive: as an example one dab of pure 3,4-benzopyrene gave an almost 100% probability of inducing a tumour. Now that is a far greater concentration than any person will get smoking, and people are not rats, nevertheless this showed me that on any reasonable assessment, smoking is a bad idea. (It was also a bad idea for a young organic chemist: who needs an ignition source a few centimeters in front of the face when handling volatile solvents?) Yet fifty years or so later, people continue to smoke. It seems to be a Faustian attitude: the cancer will come decades later, or for some lucky ones, not at all, so ignore the warning.

A similar situation is occurring now with climate change. The critical piece of information for me is that during the 1990s and early 2000s (the period of the study) it was shown there is a net power input to the oceans of 0.64 W/m2. If there is a continuing net energy input to the oceans, they must be warming. Actually, the Tasman has been clearly warming, and the evidence from other oceans supports that. So the planet is heating. Yet there are a small number of “deniers” who put their head in the sand and refuse to acknowledge this, as if by doing so, the problem goes away. Scientists seem unable to make people fact up to the fact that the problem must be dealt with now but the price is not paid until much later. As an example, in 2014 US Senate majority leader Mitch McConnell said: “I am not a scientist. I’m interested in protecting Kentucky’s economy.” He forgot to add, now.

The problem of ignoring what you do not like is general and pervasive, as I quickly learned while doing my PhD. My PhD was somewhat unusual in that I chose the topic and designed the project. No need for details here, but I knew the department, and my supervisor, had spent a lot of effort establishing constants for something called the Hammett equation. There was a great debate going on whether the cyclopropane ring could delocalise electronic charge in the same way as a double bond, only mre weakly. This equation would actually address that question. The very limited use of it by others at the start of my project was inconclusive, for reasons we need not go into here. Anyway, by the time I finished, my results showed quite conclusively that it did not, but the general consensus, based essentially on the observation that positive electric charge was strongly stabilised by it, and on molecular orbital theory (which assumes it initially, so was hardly conclusive on this question) was that it did. My supervisor made one really good suggestion as to what to do when I ran into trouble, and this was the part that showed the effect the most. But when it became clear that everyone else was agreeing the opposite and he had moved to a new position, he refused to publish that part.

This was an example of what I believe is the biggest failing. The observation everyone clung to was unexpected and needed a new explanation, and what they came up with most certainly gave the right answer for that specific case. However, many times there is more than one possible explanation, and I came up with an alternative based on classical electric field theory, that also predicted positive charge would be stabilized, and by how much, but it also predicted negative charge would be destabilized. The delocalization concept required bothto be stabilised. So there was a means of distinguishing them, and there was a very small amount of clear evidence that negative charge was destabilised. Why a small amount of evidence. Well, most attempts at making such compounds failed outright, which is in accord with the compounds being unstable but it is not definitive.

So what happened? A review came out that “convincingly showed” the answer was yes. The convincing part was that it cited a deluge of “me too” work on the stabilization of positive charge. It ignored my work, and as I later found out when I wrote a review, it ignored over 60 different types of evidence that showed results that contradicted the “yes” answer. My review was not published because it appears chemistry journals do not publish logic analyses. I could not be bothered rewriting, although the draft document is on the web if anyone is interested.

The point this shows is that once a paradigm is embedded, even if on shaky grounds, it is very hard to dislodge, in accord with what Thomas Kuhn noted in “The structure of scientific revolutions”. One of the points Kuhn noted was if the paradigm had evidence, scientists would rush to write papers confirming the paradigm by doing minor variations on what worked. That happened above: they were not interested in testing the hypothesis; they were interested in getting easy papers published to advance their careers. Kuhn also noted that observations that contradict the paradigm are ignored as long as they can be. Maybe over 60 different types of observations that contradict, or falsify, the paradigm is a record? I don’t know, but I suspect the chemical community will not be interested in finding out.

Processing Minerals in Space

I have seen some recent items on the web that state that asteroids are full of minerals and fortunes await. My warning is, look deeper. The reason is, most asteroids have impact craters, and from basic physics but some rather difficult calculations you can show these were formed from very energetic collisions. That the asteroid did not fly to bits indicates it is a solid with considerable mechanical strength. That implies the original dust either melted to form a solid, or a significant chemical reaction took place. For those who have read my “Planetary Formation and Biogenesis” you will know why they melted, assuming I am right. So what has that got to do with things? Quite simply, leaving aside metals like gold, the metal oxides in molten silica form the olivine or pyroxene families, or aluminosilicates. That is they form rocks. To give an example of the issue, I recently read a paper where various chondrites were analysed, and the method of analysis recorded the elements separately. The authors were making much of the fact that the chondrites contained 19% iron. Yikes! But wait. Fayalite contains almost 55% iron by weight, but it is useless as an ore. The olivine and pyroxene structures have tetrahedral silicon oxides (the pyroxene as a strand polymer) where the other valence of the oxygen is bound to a divalent cation, mostly magnesium because magnesium is the most common divalent element in the supernova dust. What these authors had done was to analyse rock.

If you read my previous post you will see that I have uncovered yet another problem with science: the authors were very specialized but they went outside their sphere of competency, quite accidentally. They cited numbers because so much in science depends on numbers. But it is also imperative to know what the numbers mean.

On Earth, most of the metals we obtain come from ores, which have formed through various forms of geochemical processing. Thus to get iron, we usually process haematite, which is an iron oxide, but the iron almost certainly started as an average piece of basalt that got weathered. It is most unlikely that good deposits of haematite will be found on asteroids, although it is possible on Mars where small amounts have been found. If Mars is to be settled, processing rocks will be mandatory for survival but the problems are different from those of asteroids. For this post, I wish to restrict myself to discussing asteroids as a source of metals. Let us suppose an asteroid is collected and brought to a processing site, the question is, what next?

The first problem is size-reduction, i.e.breaking it down to more manageable pieces. How do you do that? If you hit it with something, you immediately separate, following Newton’s third law. If you want to see the difficulties, stand on a small raft and try to keep on hitting something. Ah, you say, anchor yourself. How? You have to put something like a piton into solid rock, and how do you do that without some sort of impact? Of course it can be done, but it is not easy. Now you start smashing it. What happens next is bits of asteroid fly off into space. Can you collect all of the pieces? If not, you are a menace because the asteroid’s velocity v, which will be in the vicinity of 30 km/s if near Earth, has to be added to whatever is given to the fragments. Worse, they take on the asteroid’s eccentricity ε(how much difference there is between closest and farthest distance from the sun) and whatever eccentricity has been added by the fragmentation. This is important because the relative velocity of impact assuming the target is on a circular orbit is proportional to εv. Getting hit by a rock at these sort of velocities is no joke.

However, suppose you collect all the rock, you have two choices: you can process the rock as is, or you can try to refine it. If you adopt the latter idea, how do you do it? On Earth, such processing arises through millions of years of action with fluids, or through superheated fluids passing through high temperature rock. That does not sound attractive. Now some asteroids are argued to have iron cores so the geochemical processing has been done for you. Of course you still have to work your way through the rock, and then you have to size reduce the iron, which again raises the question, how? There is also a little less good news awaiting you: iron cores are almost certainly not pure iron. The most likely composition is iron with iron silicide, iron phosphide, iron carbide and a lot of iron sulphide. There will also be some nickel, together with corresponding compounds, and (at last joy?) certain high value metals that dissolve in iron. So what do you do with this mess?

Then, supposing you separate out a pure chemical compound, how do you get the metal out? The energy input required can be very large. Currently, there is a lot of effort being put into removing CO2from the atmosphere. The reason we do not pull it apart and dump the carbon is that all the energy liberated from burning it has to be replaced, i.e.a little under 400 kJ/mol. and that is such a lot of energy. Consider that as a reference unit. It takes roughly two such units to get iron from iron oxide, although you do get two iron atoms. It takes about five units to break forsterite into two magnesium atoms and one silicon. It takes ten such units to break down kaolinite to get two aluminium atoms and two silicon atoms. Breaking down rock is very energy intensive.

People say, electrolysis. The problem with electrolysis is the material has to dissolve in some sort of solvent and then be separated into ions. Thus when making aluminium, bauxite, an aluminium oxide is used. Clays, which are aluminosilicates such as kaolinite or montmorillinite, are not used, despite being much cheaper and more easily obtained. In asteroids any aluminium will almost certainly be in far more complicated aluminosilicates. Then there is the problem of finding a solvent for electrolysis. For the least active metals, such as copper, water is fine, but that will not work for the more active ones, such as aluminium. Titanium would be even more difficult to make, as it is made from the reduction of titanium tetrachloride with magnesium. You have to make all the starting materials!

On Earth, many oxides are reduced to metal by heating with carbon (usually very pure coal) and allow the carbon to take the oxygen and disappear as a gas. The problem with that, in space, is there is no readily available source of suitable carbon. Carbonaceous chondrites have quite complicated molecules. The ancients used charcoal, and while this is NOT pure carbon, it is satisfactory because the only other element there in volume tends to be oxygen. (Most charcoal is about 35% oxygen.) The iron in meteors could certainly be useful, but for some other valuable elements, such as platinum, while it may be there as the element, it will probably be scattered through the matrix and be very dilute.

Undoubtedly there will be ways to isolate such elements, but such methods will probably be somewhat different from what we use. In some of my novels I have had fusion power tear the molecules to atoms, ionise them, and separate out the elements in a similar way to how a mass spectrometer works, that is they are accelerated and then bent with powerful electromagnetic fields. The “bend” in the subsequent trajectory depends on the mass of the ions, so each isotope is separated. Yes, that is fiction, but whatever is used would probably seem like fiction now. Care should be taken with any investment!

How do Rocky Planets Form?

A question in my last post raised the question of how do rocky planets form, and why is Venus so different from Earth? This will take two posts; the first covers how the planets form and why, and the second how they evolve immediately after formation and get their atmospheres.

First, a quick picture of accretion. At first, the gas cloud collapses and falls into the star, and in this stage the star the size of the sun accretes something like 2.5 x 10^20 kg per second. Call that stage 1. When the star has gobbled up most of the material, such accretion slows down, and in what I shall call stage 2 it accretes gas at least four orders of magnitude slower. The gas heats due to loss of potential energy as it falls into the star, although it also radiates heat from the dust that gets hot. (Hydrogen and helium do not radiate in the infrared easily.) In stage 1, the gas reached something like 1600 degrees C at 1 A.U. (the distance from Earth to the sun). In stage 2, because far less gas was falling in, the disk had temperatures roughly what bodies have now. Even in stage 2, standard theory has it that boulder-sized objects will fall into the star within about a hundred years due to friction with the gas.

So how did planets form? The standard explanation is that after the star had finished accreting, the dust very rapidly accreted to planetesimals (bodies about 500 km across) and these collided to form oligarchs, and in turn these collided to form planets. I have many objections to this. The reasons include the fact there is no mechanism to form the planetesimals that we assume to begin with. The calculations originally required one hundred million years (100 My) to form Earth, but we know that it had to be essentially formed well before that because the collision that formed the Moon occurred at about 50 My after formation started. Calculations solved the Moon-forming problem by saying it only took 30 My, but without clues why this time changed. Worse, there are reasons to believe Earth had to form within about 1 My of stage 2 because it has xenon and krypton that had to come from the accretion disk. Finally, in the asteroid belt there is evidence of some previous collisions between asteroids. What happens is they make families of much smaller objects. In short, the asteroids shatter into many pieces upon such collisions. There is no reason to believe that similar collisions much earlier would be any different.

The oldest objects in the solar system are either calcium aluminium inclusions or iron meteorites. Their ages can be determined by various isotope decays and both had to be formed in very hot regions. The CAIs are found in chondrites originating from the asteroid belt, but they needed much greater heat to form than was there in stage 2. Similarly, iron meteorites had to form at a temperature sufficient to melt iron. So, how did they get that hot and not fall into the sun? The only time the accretion disk got sufficiently hot at a reasonable distance from the sun was when the star was accreting in stage 1. In my opinion, this shows the calculations were wrong, presumably because they missed something. Worse, to have enough material to make the giants, about a third of the stellar mass has to be in the disk, but observation of other disks in stage 2 shows there is simply not enough mass to make the giants.

The basic argument I make is that whatever was formed in the late stages of stellar accretion stayed more or less where it was. One of the puzzles of the solar system is that most of the mass is in the star, but most of the angular momentum resides in the planets, and since angular momentum has to be conserved and since most of that was with the gas initially, my argument is any growing solids took angular momentum from the gas, which sends then mass further from the star, and it had to be taken before the star stopped accreting. (I suggest a mechanism in my ebook.)

Now to how the rocky planets formed. During primary stellar accretion, temperatures reached about 1300 degrees C where Mars would form and 1550 degrees C a little beyond where Earth would grow. This gives a possible mechanism for accretion of dust. At about 800 degrees C silicates start to get sticky, so dust can accrete into small stones there, and larger ones closer to the star. There are a number of different silicates, all of which have long polymers, but some, especially aluminosilicates are a little more mobile than others. At about 1300 degrees C, calcium silicate starts to phase separate out, and about 1500 degrees C various aluminosilicates phase separate. This happens because the longer the polymer, the more immiscible it is in another polymer melt (a consequence of the first two laws of thermodynamics, and which makes plastics recycling so difficult.) If this were the only mechanism for forming rocky planets, the size of the finished planet would diminish significantly with distance from the star. Earth, Venus and Mercury are in the wrong order. Mercury may have accreted this way, but further out, stones or boulders would be the biggest objects.

Once primary stellar accretion ends, temperatures were similar to what they are now. Stones collide, but with temperatures like now, they initially only make dust. There is no means of binding silicates through heat. However, if stones can come together, dust can fill the spaces. The key to rocky planet formation is that calcium silicate and calcium aluminosilicates could absorb water vapour from the disk gases, and when they do that, they act as cements that bind the stones together to form a concrete. The zone where the aluminosilicates start to get formed is particularly promising for absorbing water and setting cement, and because iron starts to form bodies here, lumps of iron are also accreted. This is why Earth has an iron core and plenty of water. Mars has less water because calcium silicate absorbs much less water, and its iron is mainly accreted as fine dust.

Finally, Mars is smaller because the solids density is less, and the disk is cleared before it has time to fully grow. The evidence for the short-lived disk is from the relatively small size of Jupiter compared with corresponding planets around similar sized stars that our sun cleared out the accretion disk sooner than most. This is why we have rocky planets, and not planets like the Neptune-sized planets in the so-called habitable zone around a number of stars. Venus is smaller than Earth because it was harder to get going, through the difficulty of water setting the cement, which is partly why it has very little water on its surface. However, once started it grows faster since the density of basaltic rocks is greater. Mercury is probably smaller still because it formed a slightly different way, through excessively mobile silicates in the first stage of the accretion disk, and by later being bombed by very large rocky bodies that were more likely to erode it. That is somewhat similar to the standard explanation of why Mercury is small but has a large iron core. The planets grow very quickly, and soon gravity binds all dust and small stones, then as it grows, gravity attracts objects that have grown further away, which perforce are large, but still significantly smaller than the main body in the zone.

Next post: how these rocky planets started to evolve to where they are now.

Science in Action – or Not

For my first post in 2019, I wish everyone a happy and prosperous New Year. 2018 was a slightly different year than most for me, in that I finally completed and published my chemical bond theory as an ebook; that is something I had been putting off for a long time, largely because I had no clear idea what to do with the theory. There is something of a story behind this, so why not tell at least part of it in my first blog post for the year? The background to this illustrates why I think science has gone slightly off the rails over the last fifty years.

The usual way to get a scientific thought over is to write a scientific paper and publish it in a scientific journal. These tend to be fairly concise, and primarily present a set of data or make one point. One interesting point about science is that if it is not in accord with what people expect, the odds on are it will be ignored, or the journals will not even accept it. You have to add to what people believe to be accepted. As the great physicist Enrico Fermi once said, “Never underestimate the joy people derive from hearing something they already know.” Or at least think they know. The corollary is that you should never underestimate the urge people have to ignore anything that seems to contradict what they think they know.

My problem was I believed the general approach to chemical bond theory was wrong in the sense it was not useful. The basic equations could not be solved, and progress could only be made through computer modelling, together with as John Pople stated in his Nobel lecture, validation, which involved “the optimization of four parameters from 299 experimentally derived energies”. These validated parameters only worked for a very narrow range of molecules; if they were too different the validation process had to be repeated with a different set of reference molecules. My view of this followed another quote from Enrico Fermi: I remember my friend Johnny von Neumann used to say, “with four parameters I can fit an elephant and with five I can make him wiggle his trunk.” (I read that with the more modern density functional theory, there could be up to fifty adjustable parameters. If after using that many you cannot get agreement with observation, you should most certainly give up.)

Of course, when I started my career, the problem was just plain insoluble. If you remember the old computer print-out, there were sheets of paper about the size of US letter paper, and these would be folded in a heap. I had a friend doing such computations, and I saw him once with such a pile of computer paper many inches thick. This was the code, and he was frantic. He kept making alterations, but nothing worked – he always got one of two answers: zero and infinity. As I remarked, at least the truth was somewhere in between.

The first problem I attacked was the energy of electrons in the free atoms. In standard theory, the Schrödinger equation, when you assume that an electron in a neutral atom sees a charge of one, the binding energy is far too weak. This is “corrected”througha “screening constant”, and each situation had its own “constant”. That means that each value was obtained by multiplying what you expect by something to give the right answer. Physically, this is explained by the electron penetrating the inner electron shells and experiencing greater electric field.

What I came up with is too complicated to go into here, but basically the concept was that since the Schrödinger equation (the basis of quantum mechanics) is a wave equation, assume there was a wave. That is at odds with standard quantum mechanics, but there were two men, Louis de Broglie and David Bohm, who had argued there was a wave that they called the pilot wave. (In a recent poll of physicists regarding which interpretation was most likely to be correct, the pilot wave got zero votes.) I adopted the concept (well before that poll) but I had two additional features, so I called mine the guidance wave.

For me, the atomic orbital was a linear sum of component waves, one of which was the usual hydrogen-like wave, plus a wave with zero nodes, and two additional waves to account for the Uncertainty Principle. It worked to a first order using only quantum numbers. I published it, and the scientific community ignored it.

When I used it for chemical bond calculations, the results are accurate generally to within a few kJ/mol, which is a fraction of 1% frequently. Boron, sodium and bismuth give worse results.  A second order term is necessary for atomic orbital energies, but it cancels in the chemical bond calculations. Its magnitude increases as the distance from a full shell increases, and it oscillates in sign depending on whether the principal quantum number is odd or even, which results when going down a group of elements, that the lines joining them zig zag.

Does it matter? Well, in my opinion, yes. The reason is that first it gives the main characteristics of the wave function in terms only of quantum numbers, free f arbitrary parameters. More importantly, the main term differs depending on whether the electron is paired or not, and since chemical bonding requiresthe pairing of unpaired electrons, the function changes on forming bonds. That means there is a quantum effect that is overlooked in the standard calculations. But you say, surely they would notice that? Recall what I said about assignable parameters? With four of them, von Neumann could use the data to calculate an elephant! Think of what you could do with fifty!

As a postscript, I recently saw a claim on a web discussion that some of the unusual properties of gold, such as its colour, arise through a relativistic effect. I entered the discussion and said that if my paper was correct, gold is reasonably well-behaved, and its energy levels were quite adequately calculated without needing relativity, as might be expected from the energies involved. This drew almost derision – the paper was dated, an authority has spoken since then. A simple extrapolation from copper to silver to gold shows gold is anomalous – I should go read a tutorial. I offered the fact that all energy levels require enhanced screening constants, therefore Maxwell’s equations are not followed. These are the basic laws of electromagnetism. Derision again – someone must have worked that out. If so, what is the answer? As for the colour, copper is also coloured. As for the extrapolation, you should not simply keep drawing a zig to work out where the zag ends. The interesting point here was that this person was embedded in “standard theory”. Of course standard theory might be right, but whether it is depends on whether it explains nature properly, and not on who the authority spouting it is.

Finally, a quote to end this post, again from Enrico Fermi. When asked what characteristics Nobel prize winners had in common: “I cannot think of a single one, not even intelligence.”

Phlogiston – Early Science at Work

One of the earlier scientific concepts was phlogiston, and it is of interest to follow why this concept went wrong, if it did. One of the major problems for early theory was that nobody knew very much. Materials had properties, and these were referred to as principles, which tended to be viewed either as abstractions, or as physical but weightless entities. We would not have such difficulties, would we? Um, spacetime?? Anyway, they then observed that metals did something when heated in air:

M   + air +  heat        ÞM(calx) ±  ???  (A calx was what we call an oxide.)

They deduced there had to be a metallic principle that gives the metallic properties, such as ductility, lustre, malleability, etc., but they then noticed that gold refuses to make a calx, which suggested there was something else besides the metallic principle in metals. They also found that the calx was not a mixture, thus rust did not lead to iron being attached to a lodestone. This may seem obvious to us now, but conceptually this was significant. For example, if you mix blue and yellow paint, you get green and they cannot readily be unmixed, nevertheless it is a mixture. Chemical compounds are not mixtures, even though you might make them by mixing two materials. Even more important was the work by Paracelsus, the significance of which is generally overlooked. He noted there were a variety of metals, calces and salts, and he generalized that acid plus metal or acid plus metal calx gave salts, and each salt was specifically different, and depended only on the acid and metal used. He also recognized that what we call chemical compounds were individual entities, that could be, and should be, purified.

It was then that Georg Ernst Stahl introduced into chemistry the concept of phlogiston. It was well established that certain calces reacted with charcoal to produce metals (but some did not) and the calx was usually heavier than the metal. The theory was, the metal took something from the air, which made the calx heavier. This is where things became slightly misleading because burning zinc gave a calx that was lighter than the metal. For consistency, they asserted it should have gained but as evidence poured in that it had not, they put that evidence in a drawer and did not refer to it. Their belief that it should have was correct, and indeed it did, but this avoiding the “data you don’t like” leads to many problems, not the least of which include “inventing” reasons why observations do not fit the theory without taking the trouble to abandon the theory. This time they were right, but that only encourages the act. As to why there was the problem, zinc oxide is relatively volatile and would fume off, so they lost some of the material. Problems with experimental technique and equipment really led to a lot of difficulties, but who amongst us would do better, given what they had?

Stahl knew that various things combusted, so he proposed that flammable substances must contain a common principle, which he called phlogiston. Stahl then argued that metals forming calces was in principle the same as materials like carbon burning, which is correct. He then proposed that phlogiston was usually bound or trapped within solids such as metals and carbon, but in certain cases, could be removed. If so, it was taken up by a suitable air, but because the phlogiston wanted to get back to where it came from, it got as close as it could and took the air with it. It was the phlogiston trying to get back from where it came that held the new compound together. This offered a logical explanation for why the compound actually existed, and was a genuine strength of this theory. He then went wrong by arguing the more phlogiston, the more flammable the body, which is odd, because if he said some but not all such materials could release phlogiston, he might have thought that some might release it more easily than others. He also argued that carbon was particularly rich in phlogiston, which was why carbon turned calces into metals with heat. He also realized that respiration was essentially the same process, and fire or breathing releases phlogiston, to make phlogisticated air, and he also realized that plants absorbed such phlogiston, to make dephlogisticated air.

For those that know, this is all reasonable, but happens to be a strange mix of good and bad conclusions. The big problem for Stahl was he did not know that “air” was a mixture of gases. A lesson here is that very seldom does anyone single-handedly get everything right, and when they do, it is usually because everything covered can be reduced to a very few relationships for which numerical values can be attached, and at least some of these are known in advance. Stahl’s theory was interesting because it got chemistry going in a systemic way, but because we don’t believe in phlogiston, Stahl is essentially forgotten.

People have blind spots. Priestley also carried out Lavoisier’s experiment:  2HgO  + heat   ⇌   2Hg  + O2and found that mercury was lighter than the calx, so argued phlogiston was lighter than air. He knew there was a gas there, but the fact it must also have weight eluded him. Lavoisier’s explanation was that hot mercuric oxide decomposed to form metal and oxygen. This is clearly a simpler explanation. One of the most important points made by Lavoisier was that in combustion, the weight increase of the products exactly matched the loss of weight by the air, although there is some cause to wonder about the accuracy of his equipment to get “exactly”. Measuring the weight of a gas with a balance is not that easy. However, Lavoisier established the fact that matter is conserved, and that in chemical reactions, various species react according to equivalent weights. Actually, the conservation of mass was discovered much earlier by Mikhail Lomonosov, but because he was in Russia, nobody took any notice. The second assertion caused a lot of trouble because it is not true without a major correction to allow for valence. Lavoisier also disposed of the weightless substance phlogiston simply by ignoring the problem of what held compounds together. In some ways, particularly in the use of the analytical balance, Lavoisier advanced chemistry, but in disposing of phlogiston he significantly retarded chemistry.

So, looking back, did phlogiston have merit as a concept? Most certainly! The metal gives off a weightless substance that sticks to a particular gas can be replaced with the metal gives off an electron to form a cation, and the oxygen accepts the electron to form an anion. Opposite charges attract and try to bind together. This is, for the time, a fair description of the ionic bond. As for weightless, nobody at the time could determine the weight difference between a metal and a metal less one electron, if they could work out how to make it. Of course the next step is to say that the phlogiston is a discrete particle, and now valence falls into place and modern chemistry is around the corner. Part of the problem there was that nobody believed in atoms. Again, Lomonosov apparently did, but as I noted above, nobody took any notice of him. Of course, is it is far easier to see these things in retrospect. My guess is very few modern scientists, if stripped of their modern knowledge and put back in time would do any better. If you think you could, recall that Isaac Newton spent a lot of time trying to unravel chemistry and got nowhere. There are very few ever that are comparable to Newton.