Dark Energy

Many people will have heard of dark energy, yet nobody knows what it is, apart from being something connected with the rate of expansion of the Universe. This is an interesting part of science. When Einstein formulated General Relativity, he found that if his equations were correct, the Universe should collapse due to gravity. It hasn’t so far, so to avoid that he introduced a term Λ, the so-called cosmological constant, which was a straight-out fudge with no basis other than that of avoiding the obvious mistake that the universe had not collapsed and did not look like doing so. Then, when he found from observations that the Universe was actually expanding, he tore that up. In General Relativity, Λ represents the energy density of empty space.

We think the Universe expansion is accelerating because when we look back in time by looking at ancient galaxies, we can measure the velocity of their motion relative to us through the so-called red shift of light, and all the distant galaxies are going away from us, and seemingly faster the further away they are. We can also work out how far away they are by taking light sources and measuring how bright they are, and provided we know how bright they were when they started, the dimming gives us a measure of how far away they are. What two research groups found in 1998 is that the expansion of the Universe was accelerating, which won them the 2011 Nobel prize for physics. 

The next question is, how accurate are these measurements and what assumptions are inherent? The red shift can be measured accurately because the light contains spectral lines, and as long as the physical constants have remained constant, we know exactly their original frequencies, and consequently the shift when we measure the current frequencies. The brightness relies on what are called standard candles. We know of a class of supernovae called type 1a, and these are caused by one star gobbling the mass of another until it reaches the threshold to blow up. This mass is known to be fairly constant, so the energy output should be constant.  Unfortunately, as often happens, the 1a supernovae are not quite as standard as you might think. They have been separated into three classes: standard 1a, dimmer 1a , and brighter 1a. We don’t know why, and there is an inherent problem that the stars of a very long time ago would have had a lower fraction of elements from previous supernovae. They get very bright, then dim with time, and we cannot be certain they always dim at the same rate. Some have different colour distributions, which makes specific luminosity difficult to measure. Accordingly, some consider the evidence is inadequate and it is possible there is no acceleration at all. There is no way for anyone outside the specialist field to resolve this. Such measurements are made at the limits of our ability, and a number of assumptions tend to be involved.

The net result of this is that if the universe is really expanding, we need a value for Λ because that will describe what is pushing everything apart. That energy of the vacuum is called dark energy, and if we consider the expansion and use relativity to compare this energy with the mass of the Universe we can see, dark energy makes up 70% of the total Universe. That is, assuming the expansion is real. If not, 70% of the Universe just disappears! So what is it, if real?

The only real theory that can explain why the vacuum has energy at all and has any independent value is quantum field theory. By independent value, I mean it explains something else. If you have one observation and you require one assumption, you effectively assume the answer. However, quantum field theory is not much help here because if you calculate Λ using it, the calculation differs from observation by a factor of 120 orders of magnitude, which means ten multiplied by itself 120 times. To put that in perspective, if you were to count all the protons, neutrons and electrons in the entire universe that we can see, you would multiply ten by itself about 83 times to express the answer. This is the most dramatic failed prediction in all theoretical physics and is so bad it tends to be put in the desk drawer and ignored/forgotten about.So the short answer is, we haven’t got a clue what dark energy is, and to make matters worse, it is possible there is no need for it at all. But it most certainly is a great excuse for scientific speculation.

Is There a Planet 9?

Before I start, I should remind everyone of the solar system yardstick: the unit of measurement called the Astronomical Unit, or AU, which is the distance from Earth to the Sun. I am also going to define a mass unit, the emu, which is the mass of the Earth, or Earth mass unit.

As you know, there are eight planets, with the furthest out being Neptune, which is 30 AU from the Sun. Now the odd thing is, Neptune is a giant of 17 emu, Uranus is only about 14.5 emu, so there is more to Neptune than Uranus, even though it is about 12 AU further out. So, the obvious question is, why do the planets stop at Neptune, and that question can be coupled with, “Do they?” The first person to be convinced there had to be at least one more was Percival Lowell, he of Martian canal fame, and he built himself a telescope and searched but failed to find it. The justification was that Neptune’s orbit appeared to be perturbed by something. That was quite reasonable as Neptune had been found by perturbations in Uranus’ orbit that were explained by Neptune. So the search was on. Lowell calculated the approximate position of the ninth planet, and using Lowell’s telescope, Clyde Tombaugh discovered what he thought was planet 9.  Oddly, this was announced on the anniversary of Lowell’s birthday, Lowell now being dead. As it happened, this was an accidental coincidence. Pluto is far too small to affect Neptune, and it turns out Neptune’s orbit did not have the errors everyone thought it did – another mistake. Further, Neptune, as with the other planets has an almost circular obit but Pluto’s is highly elliptical, spending some time inside Neptune’s orbit and sometimes as far away as 49 AU from the Sun. Pluto is not the only modest object out there: besides a lot of smaller objects there is Quaoar (about half Pluto’s size) and Eris (about Pluto’s size). There is also Sedna, (about 40% Pluto’s size) that has an elliptical orbit that varies the distance to the sun from 76 AU to 900 AU.

This raises a number of questions. Why did planets stop at 30 AU here? Why is there no planet between Uranus and Neptune? We know HR 8977 has four giants like ours, and the Neptune equivalent is about 68 AU from the star, and that Neptune-equivalent is about 6 times the mass of Jupiter. The “Grand Tack” mechanism explains our system by arguing that cores can only grow by major bodies accreting what are called planetesimals, which are bodies about the size of asteroids, and cores cannot grow further out than Saturn. In this mechanism, Neptune and Uranus formed near Saturn and were thrown outwards and lifted by throwing a mass of planetesimals inwards, the “throwing”: being due to gravitational interactions. To do this there had to be a sufficient mass of planetesimals, which gets back to the question, why did they stop at 30 AU?

One of the advocates for Planet 9 argued that Planet 9, which was supposed to have a highly elliptical orbit itself, caused the elliptical orbits of Sedna and some other objects. However, this has also been argued to be due to an accidental selection of a small number of objects, and there are others that don’t fit. One possible cause of an elliptical orbit could be a close encounter with another star. This does happen. In 1.4 million years Gliese 710, which is about half the mass of the Sun, will be about 10,000 AU from the Sun, and being that close, it could well perturb orbits of bodies like Sedna.

Is there any reason to believe a planet 9 could be there? As it happens, the exoplanets encylopaedia lists several at distances greater that 100 AU, and in some case several thousand AU. That we see them is because they are much larger than Jupiter, and they have either been in a good configuration for gravitational lensing or they are very young. If they are very young, the release of gravitational energy raises them to temperatures where they emit yellow-white light. When they get older, they will fade away and if there were such a planet in our system, by now it would have to be seen by reflected light. Since objects at such great distances move relatively slowly they might be seen but not recognized as planets, and, of course, studies that are looking for something else usually encompass a wide sky, which is not suitable for planet searching.For me, there is another reason why there might be such a planet. In my ebook, “Planetary Formation and Biogenesis” I outline a mechanism by which the giants form, which is similar to that of forming a snowball: if you press ices/snow together and it is suitably close to its melting point, it melt-fuses, so I predict the cores will form from ices known to be in space: Jupiter – water; Saturn – methanol/ammonia/water; Uranus – methane/argon; Neptune – carbon monoxide/nitrogen. If you assume Jupiter formed at the water ice temperature, the other giants are in the correct place to within an AU or so. However, there is one further ice not mentioned: neon. If it accreted a core then it would be somewhere greater than 100 AU.  I cannot be specific because the melting point of neon is so low that a number of other minor and ignorable effects are now significant, and cannot be ignored. So I am hoping there is such a planet there.

Exoplanets: Do They Have Life?

One question that NASA seeks to answer is, is there life somewhere else? That raises the question, how can you tell? The simplest answer is, find something that only life can make. The problem with that is that life uses chemistry, and chemistry occurs anyway, so it is sometimes possible that what you find might be due to life, or it might be due to geophysical or geochemical action. Another problem is, some of the molecules that life makes more readily than simple geology does, say, may be difficult to find. When looking for minor traces, it is possible to find “signals” but misinterpret them. In an earlier post, I suggested the so-called signals for phosphine on Venus fell into that class, and what I have seen since reinforces that view. Many now think it was one of the signals from sulphur dioxide, which is known to be there.

One of the strongest indications we could find would be to find a number of homochiral chemicals. Thus when sugars are made chemically, say by condensing formaldehyde, they are either in the D or L configuration. Chirality can be thought of as “handedness”; your left hand is different from your right hand, and the same thing happens for chemicals used by life – life only makes one sort, the reason being that reproduction from nucleic acids only work if they can make a double helix, and that only works if there is a constant pitch, which in turn requires the linking group, the ribose, to be in one form – left or right handed. Amino acids are similar because enzymes only work in specific configurations, as do many of the other properties of proteins. The problem with chirality as evidence of life is that it is hard to measure. The usual method is to isolate the compound in a pure form in solution, pass polarised light through it, and measure the rotation of the polarization. But that really needs a chemist on the spot. Remote sensing is not really suitable. Forget that for exoplanets.

One approach has been to find a gas in the atmosphere typical of life. If you found an atmosphere with as much oxygen as Earth’s, it would almost certainly have life because oxygen cannot be accreted directly by a planet in the habitable zone. The bulk of Earth’s oxygen has probably come from photosynthesis, or the photolysis of water. The latter occurs in the absence of life, but when it does in the atmosphere, it forms ozone, which stops the reaction because water will be below the ozone. On Mars, some water has been photolysed on the surface, but  it formed peroxides or superoxides with iron oxide, or perchlorates with chlorides. So a lot of oxygen is indicative. Another gas is methane. Methane is given of by anaerobic bacteria, but it is also made geologically by reacting carbon compounds, such as the dioxide, with water and ferrous ions, which are common in the olivine-type minerals, which in turn are very common. Almost any basalt will react, in time. So methane is ambiguous.

Perhaps, we should look for more complicated molecules. There are still traps.  Recent work has shown that the chemicals that are part of the Krebs cycle, which is rather fundamental to life, actually can be made from carbon dioxide, iron, and some metal ions such as zinc. Even these are not characteristic of life, although the work may give further clues as to how life got underway, and why the chemicals used in the Krebs cycle “got involved”.

When NASA sent its Viking rovers to Mars, their approach was to treat soil samples with water and nutrients that microbes could metabolise, and then they looked to see if there were any products. One experiment detected radio-labelled gases from samples treated with carbon-14-labelled nutrients, and the idea was if the 14C got into the gas phase, where its radioactivity could be detected, it would mean life. Maybe not. If the nutrients landed on a superoxide, they would have been converted to gas. It is not easy doing this remotely.The one difference that characterises Earth when seen from space is its colour. However, the blue merely means oceans. It is possible that planets with oceans will also have what is required for life, but we could not guarantee that. If we recognised spectral signals from chlorophyll, that would be a strong indication, but whether such signals can be observed, even if there are plants there, is unclear. Again, this is not easy.

An Example of How Science Works: Where Does Gold Come From?

Most people seem to think that science marches on inexorably, gradually uncovering more and more knowledge, going in a straight line towards “the final truth”. Actually, it is far from that, and it is really a lurch from one point to another. It is true science continues to make a lot of measurements, and these fill our banks of data. Thus in organic chemistry, over the odd century or so we have collected an enormous number of melting points. These were obtained so someone else could check whether something else he had could be the same material, so it was not pointless. However, our attempts to understand what is going on have been littered with arguments, false leads, wrong turns, debates, etc. Up until the mid twentieth century, such debates were common, but now much less so. The system has coalesced in acceptance of the major paradigms, until awkward information comes to light that is sufficiently important that it cannot be ignored.

As an example, currently, there is a debate going on relating to how elements like gold were formed. All elements heavier than helium, apart from traces of lithium, were formed in stars. The standard theory says we start with hydrogen, and in the centre of a star, where the temperatures and pressures are sufficient two hydrogen atoms combine to form, for a very brief instant, helium 2 (two protons). An electron is absorbed, and we get deuterium, which is a proton and a neutron combined. The formation of a neutron from a proton and an electron is difficult because it needs about 1.3 MeV of energy to force it in, which is about a third of a million times bigger than the energy of any chemical bond. The diproton is a bit easier because the doubling of the positive field provides some supplementary energy. Once we get deuterium, we can do more and eventually get to helium 4 (two protons, two neutrons) and then it stops because the energy produced prevents the pressure from rising. The inside of the sun is an equilibrium, and in any given volume, a surprisingly few fusion reactions take place. The huge amount of energy is simply because of size. However, when the centre starts to run out of hydrogen, the star collapses further, and if it is big enough, it can start burning helium to make carbon and oxygen. Once the supply of helium becomes insufficient, if the star is large enough, a greater collapse happens, but this refuses to form an equilibrium. Atoms fuse at a great rate and produce the enormous amount of energy in a supernova.

What has happened in the scientific community is that once the initial theory was made, it was noticed that iron is at an energy minimum, and making elements heavier than iron absorb energy, nevertheless we know there are elements like uranium, gold, etc, because we use them. So how did they form? The real short answer is, we don’t know, but scientists with computers like to form models and publish lots of papers. The obvious way was that in stars, we could add a sequence of helium nuclei, or protons, or even, maybe, neutrons, but these would be rare events. However, in the aftermath of a supernova, huge amounts of energy are released, and, it is calculated, a huge flux of neutrons. That 1.3 MeV is a bit of a squib to what is available in a supernova, and so the flux of neutrons could gradually add to nuclei, and when it contained too many neutrons it would decay by turning a neutron into a proton, and the next element up, and hence this would be available form further neutrons. The problem though, is there are only so many steps that can be carried out before the rapidly expanding neutron flux itself decays. At first sight, this does not produce enough elements like gold or uranium, but since we see them, it must have.

Or must it? In 2017, we detected gravitational wave from an event that we could observe and had to be attributed to the collision of two neutron stars. The problem for heavy elements from supernovae is, how do you get enough time to add all the protons and neutrons, more or less one at a time. That problem does not arise for a neutron star. Once it starts ejecting stuff into space, there is no shortage of neutrons, and these are in huge assemblies that simply decay and explode into fragments, which could be a shower of heavy elements. While fusion reactions favour forming lighter elements, this source will favour heavier ones. According to the scientific community, problem solved.

There is a problem: where did all the neutron stars come from? If the elements come from supernovae, all we need is big enough stars. However, neutron stars are a slightly different matter because to get the elements, the stars have to collide. Space is a rather big place. Let over all time the space density of supernovae be x, the density of neutron stars y, and the density of stars as z. All these are very small, but z is very much bigger than x and x is almost certainly bigger than y. The probability of two neutron stars colliding is proportional to y squared, while the probability of a collision of a neutron stars another star would be correspondingly proportional to yz. Given that y is extremely small, and z much bigger, but still small, most neutron stars will not collide with anything in a billion years, some will collide with a different star, while very few will collide with another neutron star. There have been not enough neutron stars to make our gold, or so the claims go.So what is it? I don’t know, but my feeling is that the most likely outcome is that both mechanisms will have occurred, together with possible mechanisms we have yet to consider. In this last respect, we have made elements by smashing nuclei together. These take a lot of energy and momentum, but anything we can make on Earth is fairly trivial compared with the heart of a supernova. Some supernovae are calculated to produce enormous pressure waves, and these could fuse any nuclei together, to subsequently decay, because the heavy ones would be too proton rich.  This is a story that is unfolding. In twenty years, it may be quite different again.

Water on the Moon

The Moon is generally considered to be dry. There are two reasons for that. The first is the generally accepted model for the formation of our moon is that something about the size of Mars collided with Earth and sent a huge amount of silica vapours into space at temperatures of about 10,000 degrees Centigrade (which is about twice as hot as the average surface of the sun) and much of that (some say about half) condensed and accreted into the Moon. Because the material was so hot and in a vacuum, all water should have been in the gas phase, and very little would condense so the Moon should be anhydrous deep in the interior. The fact its volcanic emissions have been considered to be dry is taken to support that conclusion. And thus with circular logic, it supports the concept that Earth formed by objects as large as Mars colliding and forming the planet.

The second is the rocks brought back by Apollo were considered to be anhydrous. That was because the accepted paradigm for the Moon formation required it to be dry. The actual rocks, on heating to 700 degrees Centigrade, were found to have about 160 ppm of water. On the basis that the accepted paradigm required them to be anhydrous it was assumed the rocks were contaminated with water from Earth. The fact that the deuterium levels of the hydrogen atoms in this water corresponded to solar hydrogen and not Earth’s water was ignored. That could not be contamination. Did that cause us to revise the paradigm? Heavens no. Uncomfortable facts that falsify the accepted theory have to be buried and ignored.

Recently, two scientific papers have concluded that the surface of the Moon contains water. Yay! If we go there, there is water to drink. Well, maybe. First, let’s look at how we know. The support is from infrared spectra, where a signal corresponding to the O-H bond stretching mode is seen. It has been known for some time that such signals have been detected on the Moon, but this does not mean there is water, since it could also arise from entities with, say, a Si-O-H group. Accordingly, it could come from space weathered rock, and in this context, signal strength increases towards the evening, which would happen if the rocks reacted with solar wind. The heating of rocks with these groups would give off water, so the Moon might still be technically dry but capable of providing water. Further examination of apatites brought back from Apollo suggested the interior could have water up to about 400 ppm.

How could the interior be wetter? That depends on how it formed. In my ebook, “Planetary Formation and Biogenesis” I surveyed the possibilities, and I favour the proposal outlined by Belbruno, E., Gott, J.R. 2005. Astron. J. 129: 1724–1745. Quite simply, Theia, the body that collided with Earth, formed at one of the Lagrange points. I favour L4. Such a body there would accrete by the same mechanism as Earth, which explains why it has the same isotopes, and while its orbit there is stable while it is small, as soon as it becomes big it gets dislodged. It would still collide with Earth, it would still get hot but need not vaporize. Being smaller, the interior may trap its water. There is evidence from element abundance that anything that would remain solid on the surface at about 1100 degrees Centigrade was not depleted, which means that is roughly the maximum temperature reached, and that would not vaporize silicates.

In one of the new papers, the signals from the surface have included the H-O-H bending frequency, which means water. Since it has not evaporated off into space it is probably embedded in rocks and may have originated from meteorites that crashed into the Moon, where they melted on impact and embedded the water they brought. There is also ice in certain polar craters that never see the sunlight, and above latitude 80 degrees, there are a number of such small craters.So, what does this mean for settlement? If the concentration is 5 ppm, to get 5 kg of water you would have to process a thousand tonne of rock, which would involve heating it to about seven hundred degrees Centigrade, holding it there, and not letting any water escape. The polar craters have ice up to a few per cent, but that ice also contains ammonia, hydrogen sulphide, and some other nasties, and since the craters never see sunlight the outside temperature is approximately two hundred degrees Centigrade below zero. You will see proposals that future space ships will use hydrogen and oxygen made from lunar water. That would require several thousand tonne of water, which would involve processing a very large amount of rock. It will always be easier to get water from the Sahara desert than the lunar surface, but it is there and could help maintain a settlement with careful water management.

Support for a Predicted Mechanism!

What is the point of a scientific theory? The obvious one is that if you understand you can predict what will happen if you have reason to have that proposition present.  Unfortunately, you can lay down the principles and not make the specific prediction because you cannot foresee all the possible times it might be relevant. What sparked this thought is that about a decade ago I published an ebook called “Planetary Formation and Biogenesis”. The purpose of this was in part because the standard theory starts off by assuming that somehow things called planetesimals form. These were large asteroids, a few hundred km in size, and then these formed planets through their mutual gravity. However, nobody had any idea at all how these planetesimals formed; they were simply assumed as necessary on the assumption that gravity was the agent that formed the planets. On a personal level, I found this to be unsatisfactory.

I am restricting the following to what happens with icy bodies; the rocky ones are a completely different story. We start with highly dispersed dust because the heavy elements are formed in a supernova, in which these gases fly out at a very high speed. In one supernova, one hour after initiation, matter was flying out at 115,000 km/second, and it takes a long time to slow down. However, eventually it cools, gets embedded in a gas cloud and some chemical reactions take place. Most of the oxygen eventually reacts with something. All the more reactive elements like silicon or aluminium react, and the default for oxygen is to form water with hydrogen. The silicon, magnesium, calcium and aluminium oxides form solids, but they form one link at a time and cannot rearrange. This leaves a dispersion of particles that make smoke particles look large. If two such “particles” get close enough, because the chemical bonds are quite polar in these particular oxides, they attract each other and because they are reactive, they can join. This leads to a microscopic mass of tangled threads since each junction is formed on the exterior. So we end up with a very porous solid with numerous channels. These channels incorporate gases that are held to the channel surfaces. In the extreme cold of space, when these gases are brought close together on these surfaces they solidify to form ices. These solids filled with ices have been formed in the laboratory.

My concept of how icy bodies accrete goes like this. As the dust comes into an accretion disk where a star is forming, as it approaches the star it starts to warm. If particles collide at a temperature a little below the melting point of an ice they contain, the heat of collision melts the ice, the melt flows between the bodies then refreezes, gluing the bodies together. The good news is this has been demonstrated very recently in the laboratory for nanometer-sized grains of silicates coated with water ice (Nietadi et al., Icarus, (2020) 113996) so it works. As the dust gets warmer than said melting point, that ice sublimes out, which means there are four obvious different agents for forming planets through ices. In increasing temperatures these are nitrogen/carbon monoxide (Neptune and the Kuiper Belt); argon/methane (Uranus); methanol/ammonia/water (Saturn); and water (Jupiter). The good news is these planets are spread relatively to where expected, assuming the sun’s accretion disk was similar to others. So, in one sense I had a success: my theoretical mechanism gave planetary spacings consistent with observation, and now the initial mechanism of joining for very small-scale particles has been shown to work.

But there was another interesting point. Initially, when these fluffy pieces meet, they will join to give a bigger fluffy piece. This helps accretion because if larger bodies collide, the fluff can collapse, making the impact more inelastic and thus dispersing collisional energy. Given a reasonable number of significant collisions, the body will compact. If, however, there are some late gentle acquisitions of largish fluffy masses, that fluff will remain.Unfortunately, I did not issue a general warning on this, largely because nobody can think of everything, and also I did not expect that to be relevant to any practical situation now.  Rather unexpectedly, it was. You may recall that the European Space Agency landed the probe Philae on comet 67P/Churyumov–Gerasimenko, which made a couple of bounces and fell down a “canyon”, where it lay on its side. The interesting thing is the second “bounce” was not really a bounce. The space agency has been able to use the imprint of the impact to measure the strength of the ice, and  found it to be “softer than the lightest snow, the froth on your cappuccino or even the bubbles in your bubble bath.” This particular “boulder” on the outside of the comet is comprised of my predicted fluff. It feels good when something comes right. And had ESA read my ebook, maybe they would have designed Philae slightly differently.

Asteroid Mining

One thing you see often in the media is the concept that perhaps in the future we can solve our resources problem by mining asteroids. Hopefully, that is fine for science fiction, and I use that word “hopefully” because my next piece of science fiction, currently in the editing mode, includes collecting asteroids for minerals extraction. However, what is the reality?

We know we have a resource problem. An unfortunately large and growing number of elements are becoming scarcer and harder to obtain. As a consequence, ores are getting less concentrated, and so much material has to be thrown away. As an example, the earliest use of copper at around 7,000 BC used native copper. All the people had to do was take a piece and hammer it into some desirable shape. Some time later someone found that if something like malachite was accidentally in a fireplace, it got reduced to copper, and metallurgy was founded. Malachite is 57.7% copper, while if you were lucky enough to find cuprite you got a yield of almost 89% copper. Now the average yield of copper from a copper ore is 0.6% and falling. The rest is usually useless silicates. So, you may think, if we have worked through all the easily available stuff here, nobody has worked through the asteroids. There we could get “the good stuff”.

At this point it is worth contemplating what an ore is and where it came from? All the elements heavier than lithium were made in supernovae or through collisions of neutron stars. Either way, if we think of the supernova, the elements are made at an extremely high temperature, and they are flying away from the stellar core at a very high velocity. The net result is they end up as particles that make the particles in smoke look big. This “smoke” gets mixed in with gas clouds that end up making stars and planets. To get some perspective on concentrations, for every million silicon atoms you will get, on average, about 900,000 iron atoms, almost 24,000,000 oxygen atoms, 5420 chlorine atoms, 52,700 sodium atoms, 522 copper atoms, almost half a silver atom, 0.187 gold atoms, 1.34 platinum atoms and about 0.009 uranium atoms.

So what happens depends on whether the elements react in the accretion disk, so that molecules form. For example, all the sodium atoms will either form a chloride or a hydroxide, but the gold atoms will by and large not react. About half the iron atoms form an oxide or stay as the element, and the oxides will end up as silicates (basalt). What happens next depends on how the objects accrete. That is not agreed. Most scientists say they simply don’t know. I believe the bodies are accreted through chemistry. If the former, we have to assume the elements end up as a mix that have those elements in proportion, except for those that make gases. If the latter, then some will be more concentrated than others.

On earth, elements are concentrated into ores by geochemistry. The heat and water processes some elements, and heat and volcanism concentrates others. Thus gold is concentrated by it dissolving in supercritical water, together with silica, which is why you often find gold in quartz veins. The relevance to asteroids is that processing does not happen in most because they are not big enough to generate the required heat. The relevance now is that the elements you want will either be bound up with silicates, or be scattered randomly through the bulk. To get the metals out, you have to get rid of the silicates, and if you look at the figures, the copper content is actually less than in our ores on earth. Now look at the mining wastes on Earth, and ask yourself what would you do with that in space? (There is an answer – build space stations with rocky shells.)

So why do we think of mining asteroids. One reason comes from asteroid Psyche. One scientific paper once claimed asteroid had a density as high as 7.6 g/cm cubed. That would clearly be worth mining, because the iron would also dissolve nickel, cobalt, platinum, gold, etc. You will various news items that wax on about how this asteroid alone would solve our problems and make everyon extremely rich. However, other papers have published values as low as 1.4 g/cm cubed, and the average value is about 3.5 g/cm cubed (which is what it would be if it were solid basalt). 

Why the differences? Basically because density depends on the mass (determined by gravitational interactions) and volume.  The uncertainty in the volume, thanks to observational uncertainty due to the asteroid being so far away and the fact it is not round, can give an error of up to 50%. The mass requires very accurate measurements when near something else and again huge errors are possible.

So the question then is, if someone wants to get metals out of asteroids, how will they do it? If the elements are there as oxides or sulphides, what do you do about that? On Earth you heat with coal and air, followed by coal. You cannot do that in space. On Earth, minerals can be concentrated by various means that use liquids, such as froth flotation, but you cannot do that easily in space because first liquids like water are scarce, and second, if you have them, unless they are totally enclosed they boil off into space. Flotation requires “gravity”, which requires a centrifuge. Possible, but very expensive,If you were building a giant space station, yes, asteroids would be valuable because the cost of getting components from Earth is huge, but we still need technology to refine them. Otherwise the cost of getting the materials to Earth would be horrifying. Be careful if you see an investment offering.

No Phosphine on Venus

Some time previouslyI wrote a blog post suggesting the excitement over the announcement that phosphine had been discovered in the atmosphere of Venus (https://ianmillerblog.wordpress.com/2020/09/23/phosphine-on-venus/) I outlined a number of reasons why I found it difficult to believe it. Well, now we find in a paper submitted to Astronomy and Astrophysics (https://arxiv.org/pdf/2010.09761.pdf) we find the conclusion that the 12th-order polynomial fit to the spectral passband utilised in the published study leads to spurious results. The authors concluded the published 267-GHz ALMA data provide no statistical evidence for phosphine in the atmosphere of Venus.

It will be interesting to see if this denial gets the same press coverage as “There’s maybe life on Venus” did. Anyway, you heard it here, and more to the point, I hope I have showed why it is important when very unexpected results come out that they are carefully examined.

Planets Being Formed Now

An intriguing observation, recorded in Nature Astronomy3, 749 (2019) is that two planets are being formed around the star PDS 70, a star about 370 light years from Earth in the constellation of Centaurus. The star is roughly 76% the mass of the sun. Its temperature is 3972 degrees K, so it is a bit cooler than our sun, and is about 1.26 time bigger. What that means is it has yet to collapse properly. Because at least some of the accretion disk is still there, gas is still falling towards the star, and towards any planets that are still forming. Because giants have to form quickly, the huge amount of gas falling into them gets very hot, the planets glow, and if they are far enough away from the star, we can see them through very large telescopes. The first such planet to be observed in this system (Labelled PDS 70 b) is about 7 times as big as Jupiter, and is about 23 AU away from the star, i.e. it is a little further away from its star as Uranus is from our star. (1 AU is the Earth-sun distance.)

We can detect the gas flowing into the planet by the spectral signal Hα at 656.28 nm, and by selecting such a signal much of the general light is filtered out and gas can be seen streaming into planetary objects. The planet PDS 70 b was confirmed in the cited reference, but there is an addition: PDS 70 c, which is about 38 AU from its star, also with about 4 AU uncertainty. This is a bit further away from its star as Neptune is from ours, which suggests an overall system that is a bit more expanded than ours.

These planets are interesting in terms of generating a theory on how planets form. The standard theory is that dust from the accretion disk somehow accretes to form bodies about the size of asteroids called planetesimals, and through gravity these collide to form larger bodies, which in turn through their stronger gravity collide to form what are called embryos or oligarchs, and these are about the size of Mars. These then collide to form Earth-sized planets, and in the outer regions collisions keep going until the cores get to about ten times the size of Earth, then these start accreting gas, until eventually they become giants. Getting rid of heat is a problem, and consequently newly formed giants are very hot and seem like mini-stars.

The problem with that theory is timing. The further away from the star, the dust density is much lower simply because there is more space for it and even if you can form planetesimals, and nobody has any idea how they formed, the space between them gets so big their weak gravity does not lead to useful collisions. There is a way out of this in what is called the Grand Tack model. What this postulates is that Uranus and Neptune both grew a little further out than Saturn, and as they grew to be giants their gravity attracted planetesimals from further out. However, now the model argues they did not accrete them, but instead effectively pulled them in and let them go further in towards the star. By giving them inwards momentum, they got “lift” and moved out. They kept going until Neptune ran out of planetesimals, which occurred at about 32 AU.

Now, momentum is mass times velocity, which means the bigger the planet that is moving, the more planetesimals it needs, although it gets a benefit of being able to throw the planetesimal faster through its stronger gravity. That effect is partly cancelled by the planetesimals being able to pass further away. Anyway, why does a star that is about ¾ the size of our star have more planetesimals that go out almost 20% further. In fairness, you might argue that is a rather weak conclusion because the distances are not that much different and you would not expect exact correspondence. Further, while the masses of the giants are so much bigger than ours, you might argue they travelled then accreted the gas.However, there is worse. Also very recently discovered by the same technique are two planets around the young star TYC 8998-760-1, which is about the same size as the sun. The inner planet has a mass of 14 times that of Jupiter and is 162 AU from the star, and the outer planet has a mass of 6 times that of Jupiter and is 320 AU from the star. It is difficult to believe that one star of the same size as another would inadvertently have a huge distribution of planetesimals scattered out over ten times further. Further, if it did, the star’s metallicity would have to be very much higher. Unfortunately, that has yet to be measured for this star. In my opinion, this strongly suggests that this Grand Tack model is wrong, but that leaves open the question, what is right? My usual answer would be what is outlined in my ebook “Planetary Formation and Biogenesis”, although the outer planet of TYC 8998-760-1 may be a problem. However, that explanation will have to wait for a further post but those interested can make up their minds from the ebook.

Betelguese Fades

Many people will have heard about this: recently Betelgeuse became surprisingly dim. Why would that be? First, we need to understand how a star lives. They start by burning hydrogen and making helium. This is a relatively slow process, the reason being that enormous pressures are required. The reason for this is that hydrogen nuclei repel each other very strongly when they get close, and the first step seems to be to make a helium atom with no neutrons, which is two protons bound. However, they are not bound very tightly, and the electric force between them makes them fly apart in an extremely short time. Somewhere within this time, the pressure/temperature has to force an electron into one of the nuclei to transform it into a neutron, when we have deuterium, which is stable. The deuterium goes on to make the rather stable helium nuclei, and liberate a lot of energy per reaction. However, the probability of such reactions is surprisingly low, mainly because of the difficulty in making 2He. The rate is increased by temperature and pressure, but the energy liberated pushes the rest of the matter away, so an equilibrium is formed. The reason the sun pours out so much energy is because the sun is so big. The bigger the star, the more the central pressure, and the faster it can burn its hydrogen, so paradoxically the bigger the star the sooner it runs out of fuel.

Betelgeuse is the tenth brightest star in the night sky, and after Rigel, the second brightest in the constellation of Orion. It has a mass somewhere between 10 – 20 times that of the sun, so at its centre the pressure due to gravitation will be far greater than our sun, hydrogen would have burned much faster, and accordingly, it has run out of hydrogen fuel so much more quickly. When it does, if it is big enough, its core collapses somewhat due to the loss of repulsive energy until it gets hot enough to burn helium, which releases so much more energy that the outer part of the star bloats. If placed in the centre of the solar system, the surface of Betelgeuse would come close to the orbit of Jupiter. All the rocky bodies would be gone. As it grows to that size, it is not really in equilibrium. If it bloats too far, the pressure drops, the outer surface collapses, the pressure increases, reactions go faster, it expands, and so on. The periods of such pulsations can be up to thousands of days. When they pulsate, we see that as a fluctuation in brightness. It will keep pulsating and behaving errtatically until sometime, most probably within the next 100,000 years, it will collapse and form a supernova. As a star like Betelgeuse pulsates, it brightens and dims. All very expected, but recently it has dimmed to about 40% of what it was before. Was this the prelude to a supernova? The short answer is, we don’t know, but the pulsations got our attention.

Because of the size, the gravity is weaker on the surface, and huge bursts of energy send gas as a burst out into nearby space. While we have our solar winds and coronal mass ejections, those of a red supergiant are somewhat more massive, and they send out massive clouds of gas and dust. One of the first “guesses” as to the cause of the dimming was the blocking of light by dust, but further studies showed that that cannot be the case because the spectral data was more consistent with a significant mean surface cooling. Further, Betelgeuse is close enough that major telescopes can resolve the star as a ball, and it was found that between 50 – 70% of the star’s surface was significantly cooler than the rest. The star appears to have a massive star spot! So, for the time being it seems likely that Betelguese will last a little longer. As an aside, do not feel sorry for life on a planet aorund it. Betelguese is only about 20 million years old. There is no time for life to develop around such massive stars.