Cosmic Catastrophes

Astronomers have found a record explosion (Monthly Notices of the Royal Astronomical Society, Volume 522, Issue 3, July 2023, Pages 3992-4002, https://doi.org/10.1093/mnras/stad1000) . The total energy output was stated to be 1.5 x 10^53 ergs. (People still use ergs??) An erg is 10^-7 of a Joule, so the explosion generated 1.5 x 10^46 Joules. These numbers are sort of mind-boggling. Try thinking of tonnes of TNT. The equivalent would be about 3.4 x 10^36 tonnes, or well over 10^28 of the largest hydrogen bombs ever exploded. That is 10 with 28 zeros after it. Of course we can hardly see it. It is about eight billion light years away, which is probably just as well. It is more than ten time brighter than any supernova ever recorded and so far has been going for three years. The “fireball” is about 100 times the size of the solar system and that mass is two trillion times brighter than the sun. If you want to impress your friends, the explosion is known as AT2021lwx. Astronomers have charming names for things.

So what could have caused it? One option would be a tidal disruption event. This is essentially when a star is tidally disrupted by the black hole and the black hole disrupts the star, leading to star matter pouring into the black hole. Oddly enough, this depends on a tidal radius, which in turn depends on the density of the star, so that for a given stellar mass and radius there is a corresponding upper black hole mass for which this cannot occur. Larger is not better for this. For this to be the cause of this event, the star would have to be almost fifteen times the mass of the sun, which is somewhat unlikely because such a massive star only lives for about 15 million years. It is hard to see how such a massive star could be born there, because the black hole would consume the gas first, and it  is hard to see how it could move there, so that is probably not the cause.

A better alternative is thought to be a vast cloud of gas, probably thousands of times more massive than the sun, falling into a black hole. The energy is simply gravitational potential energy being converted to heat as the gas falls towards the black hole and it estimated the temperature reached about 13,000 degrees C. The gas and dust was believed to be in a disk circulating the black hole, and something must have dislodged it and made it start to fall into the black hole. However, so far nothing has been modelled.

So, at the end of the day, we don’t know what it is.

On a much much smaller scale astronomers have noticed a optical outburst named ZTF SLRN-2020 (Nature, 617: 38 – 39) that lasted roughly ten days, and then slowly decayed over six months. The start of the burst coincided with infrared emission that lasted long after the optical emission had decayed. The optical radiation was featureless continuous emission at the red end, as well as lines corresponding to molecular absorption.

The first thought was this was a classical nova. This appears to happen when a white dwarf accretes hydrogen from a close companion star. A white dwarf is effectively a dead star, and is what is left over after nuclear fusion has stopped. They have the mass of the sun and the size of Earth, so they are dense. Hydrogen landing on it will trigger nuclear fusion. However, if this were the cause we would expect to see spectral lined from elements entrained in the gas and we don’t.

Another possibility was a so-called red nova, which is caused by two stars merging. The nature of the light is quite similar, except the power output was far too small. Further, the star’s radius did not change appreciably. After some very detailed observing, they found the source was a sun-like star and the power output was consistent with the other object that did the merging being a giant planet. So it appears the star has swallowed a planet.

How would it do that? If planets get too large for the distance between them, gravity drives them into elliptical orbits with exchanged energy, i.e. one goes closer to the star and one goes further. If the exchange of angular momentum leads to the inner one having a very high eccentricity, its perigee can have a close enough approach to the star that frictional interactions cause the orbit to decay. Once that starts there is no escape for the planet.

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Lunar Water

Currently, if people go to the Moon, they will have to take everything they need with them. Shelter might be able to use some local materials, but almost everything else will have to come from Earth. Tools and manufactured items obviously have to be taken, but so must food, air and water. But what happens in the longer run? The expenses that will be run up like that will mean that the Moon will remain a useless lump of rock unless some alternatives are found.

A recent paper (He et al. Nature geoscience https://doi.org/10.1038/s41561-023-01159-6 ) claimed that the Changé-5 rover found water of about 1mg/g in glass beads formed by impacts. They then estimated that there were enough such glass beads across the lunar surface to get 2.7 x 10^14 kg of water. An interesting point was that the water had the D/H ratio approximately equal to solar hydrogen, and the authors proposed the water was imprinted into the beads by the solar wind. Looks like the problem is solved: the surface area of the Moon is 38 million square km, so one square kilometre will give you 7,000 t of water. If there is that much water in glass beads, and we would have at least 7 million t of such glass beads per square km, why did none of the Apollo samples bring back any of these glass beads? My guess is this is something of a gross overestimate. I have no doubt there are glass beads and they truly found water in them, but sorry, the estimate of how many there are must be wrong. The rover may have accidentally found a good deposit.

So that raises the question, is there water on the Moon? First, the information here is mixed. There is a dreadful bias to find what you expect. The original samples brought back from the Apollo missions had a water content, but the people who found it assumed it came from absorption when the samples were on Earth so they disregarded the water. Interestingly, the samples had a D/H ratio that was effectively solar, so the water could not have come from Earth. So the preconceived notion that the moon was anhydrous meant that the possibility of humans staying there for any length of time was not considered to be serious. Had it been found that there was water, maybe the Apollo program would not have been terminated and maybe the space station would not have been built as more effort would focus on the Moon. The history of space travel changed by “I know best”.

“Water” formed by solar winds is well established,  but it is formed as hydroxyl groups. With silicates, the outer surface does not properly complete its bonding, so hydrogen atoms can convert lone oxygen radicals to hydroxyls. The other half of the bond would be a radical that could react with water in the solar wind. That this probably happens is found by the “water” giving a reasonable spectroscopic signal in the evening, but is much weaker during the lunar morning. There are other samples that have  been shown to contain low levels of water. Apatites returned by Apollo had water up to 200 ppm, and some unusual volcanic glasses had water up to 46 ppm. Even more surprising is a claim that one sample of lunar soil contained nitrogen in low levels, and that nitrogen was not solar as it had enhanced levels of 15N.

So, there is water on the Moon. The TV program, “For All Humanity” had a lunar research settlement beside a crater where, deeper down the sun never penetrated. There was ice. Ridiculous? Not at all because NASA crashed a vehicle into such a region and found water of very approximately 5.6% by mass. Associated with the water was (as a % of the water) H₂S 16.5%, NH₃ 6%, SO₂ 3.2%, ethylene 3.1%, CO₂ 2.2%, methanol 1.6%, methane 0.7% (Colaprete et al. 2010 Science 330: 463-468). The water would be trapped as ice in regions where the sun does not strike, as these get extremely cold, rock being a very poor conductor of heat. It has been estimated that at latitudes greater than 80 degrees, water could be trapped in parts of craters that get no sunlight. Where did those minor materials come from? The assumption is that in this case the Moon was struck by some cometary material, and the temporary atmosphere was cold-trapped.

Water is indeed critical, but in some ways nitrogen is even more critical. Going in and out of a habitat is bound to lose air, and nitrogen is critical to dilute oxygen. It is also critical if you want to grow plants. Whether we would want to stay on the Moon for long is a matter of opinion, but at least now it may be more a possibility.

The Biggest Problem of Them All

From Physics World, something unexpected. The “problem” is, er, the Universe. Problems don’t come much bigger! To put this in perspective, the major theory used to describe it is Einstein’s General Relativity. There is only one problem with that theory: everything should collapse into a singular “point” and it doesn’t. To get around that problem, Einstein introduced something he called “the Cosmological Constant”, which effectively was something pulled out of thin air in an ad hoc way to at least admit the obvious problem that the Universe remained large. Worse, this steady universe could not be extrapolated to the infinite past. Somewhere along the line it had to be different from now. It was then that Georges Lemaȋtre proposed a theory that space was expanding, to which Einstein replied that his maths were correct, but his physics abominable. However, Einstein had to backtrack because Hubble showed it was expanding. (Actually, Lemaȋtre had provided evidence, but Hubble’s was better.) The idea was that all matter started from a point, and space expanded to let the energy collapse into matter. Fred Hoyle jokingly referred to this as “The Big Bang”.

All was well. Space was expanding uniformly, so the galaxies were moving away from each other uniformly, on a very large scale, but with localized variation in between. Why space was expanding was left unanswered. Thus on a very large scale, the gravitational interactions between distant galaxies was diminishing, which violates the concept of the law of conservation of energy. (Energy does not have to be conserved, though. Energy is a tricky topic in general relativity.) Hoyle was keen on a steady state universe, and while he accepted the Universe was expanding, he took the idea that if everything was moving apart, that loss of gravitational energy was made up for by the creation of new matter. This was not generally accepted, and the question of this energy imbalance remained.

There is worse. To maintain a constant expansion rate, general relativity requires a constant energy density, and how can that arise when space is expanding? The only way would seem to be that this energy density is a property of vacuum. Vacuum is, therefore, not nothing. There is nothing like an opportunity in physics to get speculation going, and “not nothing” is such an opportunity. Quantum field theory announced the vacuum is full of extraordinarily tiny harmonic oscillators, which convey a zero point energy to space. We have our energy accounted for. All was good, until it wasn’t. It was obvious to take the quantum field theory and see if it fitted with observation on galaxies. It did not. In fact the error was a factor of ten multiplied by itself 120 times (Adler, R. J., Casey, B., Jacob, O. C. 1995. Vacuum catastrophe: an elementary exposition of the cosmological constant problem. Am J. Phys 63: 620 – 626.) This was the most horrendous disagreement between calculation and observation ever.

Then came a shock: not only were the galaxies moving apart, but such motion was accelerating. This was caused, in terms of labelling, by something called dark energy. It should be noted that at this point, dark energy is merely a term that essentially is a holding term to recognize that something must be causing the acceleration. So, what is it? The good news is that whatever it is can also account for the general expansion. All we need is something that is getting bigger as the universe expands.

Now, we have a proposition, which is called “cosmological coupling”. The concept starts with the observation that the  mass of black holes at the heart of distant galaxies have been growing about ten times faster than simply accreting mass or merging with other black holes would allow. The coupling means that the growth of the black holes matched the accelerating expansion of the universe. The concept seems to be that the singularity of black holes is replaced by additional “vacuum energy”. Their coupling means that if the volume of the universe doubles, so does the mass of black holes, but the number of black holes remains constant. The logic is that “something” must give rise to the expansion of the universe, and since no other object exhibits similar behaviour, black holes must be the “something”. Is that valid? There is a problem for me with that explanation, apart from the fact that correlation does not mean causation. The evidence is the Universe took on massive expansion initially, then calmed down, and then the expansion accelerated again. During the initial expansion there would be few if any black holes. Then, suddenly, there was a massive growth of them, but that happened at a time when the universe expansion was at its slowest, then when the final acceleration started, the black holes had settled down to minimal growth. The required correlation for the hypothesis seems to be, if anything, an anti correlation.

Solar Cycles

As you may know, our sun has a solar cycle of about 11 years, and during that time the sun’s magnetic field changes, oscillating between very strong then there is a minimum, then back to the next cycle. During the minimum, there are far fewer sunspots, and the power output is also at a minimum. The last minimum started about 2017, so now we can expect increased activity. It may come as something of a disappointment that some of the peak temperatures here happened during solar minima as we can expect that the next few years will be even hotter and the effects of climate change more dramatic, but that is not what this post is about. The question is, is out sun a typical star, or is it unusual?

That raises the question, if it were unusual, how can we tell?

The power output may vary, but not extremely. The output generally is reasonably constant. We can attribute the variation in the solar output we receive over different years of about 0.1% of a degree Kelvin (or Centigrade) to that. There may appear to be more greater changes as the frequency and strength of aurorae are more significant. So how do we tell whether other stars have similar cycles? As you might guess, the power input from other stars is trivial compared even with that small variation. Any variation in total power output would be extremely difficult to detect, especially over time since instrument calibration could easily vary by more. A non-scientist may have trouble with this statement, but it would be extremely difficult to make a sensitive instrument that would record a dead flat line for a tiny constant power source over an eleven-year period. Over shorter time periods the power input from a star does vary in a clearly detectable way, and has been the basis of the Kepler telescope detecting planets.

However, as outlined in Physics World (April 5) there is a way to detect changes in magnetic fields. Stars are so hot they ionize elements, and some absorption lines in the spectrum due to ionized calcium happen to be sensitive to the stellar magnetic field. One survey showed that about half the stars surveyed appeared to have such starspot cycles, and the periodic time could be measured for half of those with the cycles. It should be noted that the inability to detect the lines does not mean the star does not have such a cycle; it may mean that, working at the limits of detection anyway, the signals were too weak to be certain of their presence.

The average length of the length of such solar cycles was about ten years, which is similar to our sun’s eleven-year cycle, although one star had a cycle lasting four years. One star, HD 166620 had a cycle seventeen years long, although “had” is the operative tense. From somewhere between 1995 and 2004, HD 166620’s starspot cycle simply turned off. (The uncertainty in the timing was because the study was discontinued due to a change of observatories, and it changed to one receiving an upgrade that was not completed until 2004.) We now await it starting up again.

Maybe that could be a long wait. In 1645 the Sun entered what we call the Maunder minimum. During the bottom of a solar cycle we would expect at least a dozen or so sunspots per year, and at the maximum, over 100. Between 1672 and 1699 fewer than 50 sunspots were observed. It appeared that for about 70 years the sun’s magnetic field was mostly turned off. So maybe HD 166620 is sustaining a similar minimum. Maybe there is a planet with citizens complaining about the cold.

What causes that? Interestingly, (Metcalfe et al. Astrophys. J. Lett. 826 L2 2016) showed that by correlating stellar rotation with age for stars older than the sun, while stars start out spinning rapidly, magnetic braking gradually slows them down, and as they slow it is argued that Maunder Minimum events may become more regular, and eventually the star slows sufficiently that the dynamo effect is insufficient and they enter a grand minimum. So eventually the Sun’s magnetic dynamo may shut down completely. Apparently, some stars display somewhat chaotic activity, some have spells of lethargy, thus HD 101501 shut down between 1980 – 1990, before reactivating, a rather short Maunder Minimum.

So when you hear people say the sun is just an average sort of star, they are fairly close to the truth. But when you hear them say the power output will steadily increase, that may not be exactly correct.

Success! Defence Against Asteroids

Most people will know that about 64 million years ago an asteroid with a diameter of about 10 km struck the Yucatán peninsula and exterminated the dinosaurs, or at least did great damage to them from which they never recovered. The shock-wave probably also initiated the formation of the Deccan Traps, and the unpleasant emission of poisonous gases which would finish off any remaining dinosaurs. The crater is 180 km wide and 20 km deep. That was a very sizeable excavation. Rather wisely, we would like to avoid a similar fate, and the question is, can we do anything about it? NASA thinks so, and they carried out an experiment.

I would be extremely surprised if, five years ago, anyone reading this had heard of Dimorphos. Dimorphos is a small asteroid with dimensions about those of the original Colosseum, i.e.  before vandals, like the Catholic Church took stones away to make their own buildings. By now you will be aware that Dimorphos orbits another larger asteroid called Didymos. What NASA has done was to send a metallic object of dimensions 1.8 x 1.9 x 2.6 meters, of mass 570 kg, and velocity 22,530 km/hr to crash into Dimorphos to slightly slow its orbital speed, which would change its orbital parameters. It would also change then orbital characteristics of the two around the sun. Dimorphos has a “diameter” of about 160 m., Didymos about 780 m. Neither are spherical hence the quotation marks.

This explains why NASA selected Dimorphos for the collision. First, it is not that far from Earth, while the two on their current orbits will not collide with Earth on their current orbits. Being close to Earth, at least when their orbits bring them close, lowers the energy requirement to send an object there. It is also easier to observe what happens hence more accurately determine the consequences. The second reason is that Dimorphos is reasonably small and so if a collision changes its dynamics, we shall be able to see by how much. At first sight you might say that conservation of momentum makes that obvious, but it is actually more difficult to know because it depends on what takes the momentum away after the collision. If it is perfectly inelastic, the object gets “absorbed” by the target which stays intact, then we simply add its relative momentum to that of the target. However, real collisions are seldom inelastic, and it would have been considered important to determine how inelastic. A further possibility is that the asteroid could fragment, and send bits in different directions. Think of Newton’s cradle. You hit one end and the ball stops but another flies off from the other end, and the total stationary mass is the same. NASA would wish to know how well the asteroid held together. A final reason for selecting Dimorphos would be that by being tethered gravitationally to Didymos, it could not go flying off is some unfortunate direction, and eventually collide with Earth. It is interesting that the change of momentum is shared between the two bodies through their gravitational interaction.

So, what happened, apart from the collision. There was another space craft trailing behind: the Italian LICIACube (don’t you like these names? It is an acronym for “Light Italian Cubesat for Imaging Asteroids”, and I guess they were so proud of the shape they had to have “cube” twice!). Anyway, this took a photograph before and after impact, and after impact Dimorphos was surrounded by a shower of material flung up from the asteroid. You could no longer see the asteroid for the cloud of debris. Of course Dimorphos survived, and the good news is we now know that the periodic time of Dimorphos around Didymos has been shortened by 32 minutes. That is a genuine success. (Apparently, initially a change  by as little as 73 seconds would have been considered a success!) Also, very importantly, Dimorphos held together. It is not a loosely bound rubble pile, which would be no surprise to anyone who has read my ebook “Planetary Formation and Biogenesis”.

This raises another interesting fact. The impact slowed Dimorphos down relative to Didymos, so Dimorphos fell closer to Didymos, and sped up. That is why the periodic time was shortened. The speeding up is because when you lower the potential energy, you bring the objects closer together and thus lower the total energy, but this equals the kinetic energy except the kinetic energy has the opposite sign, so it increases. (It also shortens the path length, which also lowers the periodic time..)

The reason for all this is to develop a planetary protection system. If you know that an asteroid is going to strike Earth, what do you do? The obvious answer is to divert it, but how? The answer NASA has tested is to strike it with a fast-moving small object. But, you might protest, an object like that would not make much of a change in the orbit of a dinosaur killer. The point is, it doesn’t have to. Take a laser light and point it at a screen. Now, give it a gentle nudge so it changes where it impacts. If the screen as a few centimeters away the lateral shift is trivial, but if the screen is a kilometer away, the lateral shift is now significant, and in fact the lateral shift is proportional to the distance. The idea is that if you can catch the asteroid far enough away, the asteroid won’t strike Earth because the lateral shift will be sufficient.

You might protest that asteroids do not travel in a straight line. No, they don’t, and in fact have trajectories that are part of an ellipse. However, this is still a line, and will still shift laterally. The mathematics are a bit more complicated because the asteroid will return to somewhere fairly close to where it was impacted, but if you can nudge it sufficiently far away from Earth it will miss. How big a nudge? That is the question about which this collision was designed to provide us with clues.

If something like Dimorphos struck Earth it would produce a crater about 1.6 km wide and 370 m deep, while the pressure wave would knock buildings over tens of km away. If it struck the centre of London, windows would break all over South-East England. There would be no survivors in central London, but maybe some on the outskirts. This small asteroid would be the equivalent a good-sized hydrogen bomb, and, as you should realize, a much larger asteroid would do far more damage. If you are interested in further information, I have some data and a discussion of such collisions in my ebook noted above.

Rotation, Rotation

You have probably heard of dark matter. It is the stuff that is supposed to be the predominant matter of the Universe, but nobody has ever managed to find any, which is a little embarrassing when there is supposed to be something like about 6 times more dark matter in the Universe than ordinary matter. Even more embarrassing is the fact that nobody has any real idea what it could be. Every time someone postulates what it is, and work out a way to detect it, they find absolutely nothing. On the other hand there may be a simpler reason for this. Just maybe they postulated what they thought they could find, as opposed to what it is, in other words it was a proposal to get more funds with the uncovering the nature of the Universe as a hoped-for by-product.

The first reason why there might be dark matter came from the rotation of galaxies. Newtonian mechanics makes some specific predictions. Very specifically, the periodic time for an object orbiting the centre of mass at a distance r varies as r^1.5. That means that say there are two orbiting objects, say Earth and Mars, where Mars is about 1.52 times more distant, the Martian year is about 1.88 Earth years. The relationship works very well in our solar system, and it was from the unexpected effects on Uranus that Neptune was predicted, and found to be in the expected place. However, when we take this up to galactic level, things come unstuck. As we move out from the centre, stars move faster than predicted from the speed of those in the centre. This is quite unambiguous, and has been found in many galaxies. The conventional explanation is that enormous quantities of cold dark matter provide the additional gravitational binding.

However, that explanation also has problems. A study of 175 galaxies showed that the radial acceleration at different distances correlated with the amount of visible matter attracting it, but the relationship does not match Newtonian dynamics. If the discrepancies are due to dark matter, one might expect the dark matter to be present in different amounts in different galaxies, and different parts of the same galaxy. Any such relationship should have a lot of scatter, but it hasn’t. Of course, that might be a result of dark matter being attracted to ordinary matter.

There is an alternative explanation called MOND, which stands for modified Newtonian gravity, which proposes that at large distances and small accelerations, gravity decays more slowly than the inverse square law. The correlation of the radial acceleration with the amount of visible matter would be required by something like MOND, so that is a big plus for it, although the only reason it was postulated in this form was to account for what we see. However, a further study has shown there is no simple scale factor. What this means is that if MOBD is correct the effects on different galaxies should be essentially dependent on the mass of visible matter but it isn’t. MOND can explain any galaxy, but the results don’t translate to other galaxies in any simple way. This should rule out MOND without amending the underlying dynamics, in other words, altering Newtonian laws of motion as well as gravity. This may be no problem for dark matter, as different distributions would give different effects. But wait: in the previous paragraph it was claimed there was no scatter.

The net result: there are two sides to this: one says MOND is ruled out and the other says no it isn’t, and the problem is that it is observational uncertainties that suggest it might be. The two sides of the argument seem to be either using different data or are interpreting the same data differently. I am no wiser.

Astronomers have also observed one of the most distant galaxies ever, MACS1149-JD1, which is over ten billion light years away, and it too is rotating, although the rotational velocity is much slower than galaxies that we see that are much closer and nowhere near as old. So why is it slower? Possible reasons include it has much less mass, hence the gravity is weaker.

However, this galaxy is of significant interest because its age makes it one of the earliest galaxies to form. It also has stars in it estimated to be 300 million years old, which puts the star formation at just 270 million years after the Big Bang. The problem with that is it is in the dark period, when matter as we know it had presumably not formed, so how did a collection of stars start? For gravity to cause a star to accrete, it has to give off radiation but supposedly no radiation was given off then. Again, something seems to be wrong. That most of the stars are just this age makes it appear that the galaxy formed about the same time as the stars, or put it another way, something made a whole lot of stars form at the same time in places where the net result was a galaxy. How did that happen? And where did the angular momentum come from? Then again, did it happen? This is at the limit of observational techniques, so have we drawn a non-valid conclusion from difficult to interpret data. Again, I have no idea, but I mention this to show there is a still a lot to learn about how things started.

Radiation Protection on Mars

The settlement of Mars is a popular science fiction staple. I have written some “Mars novels” myself. One criticism of settling Mars is that the planet does not have magnetic field to deflect radiation, so what is the situation? In my ebook “Red Gold” I suggested a magnetic field be generated by a superconductor placed between Mars and the sun, specifically at the first Lagrange point so it would be there continuously. That would divert charged particles in the solar wind. However, suppose you do not do that, what are the options. An account has been written on May 27, 2022 and is at arXiv:2205.13786.

There are two sources of radiation. The first is from the sun and consist mainly of protons, helium nuclei (5 – 8%) and heavier nuclei (~1%). These arrive with energies ranging from some keV to hundreds of MeV. Very occasionally they go to even higher energies, and their intensity varies with the solar cycle. The other source are the cosmic rays. These are accelerated by supernova shocks and interstellar magnetic fields, and appear to come evenly from all directions. They have similar composition to the solar radiation, but they arrive with far higher energies, their average being in the GeV range, and of particular hazard are the high-charge ions, thus there may be particles up to iron that are stripped of their electrons and are travelling through space near the speed of light. It is this high energy and high charge that makes them so dangerous.

The first defence Mars offers is bulk. A person standing on the Martian surface, particularly in a crater, receives less than half what they would receive in space, and that applies to cosmic rays. None of these have energy anywhere nearly enough to go through a planet. The atmosphere, while thin, offers some protection, and will remove protons with less than 150 MeV energy, and possibly more if in a deep enough crater (which is partly why in “Red Gold” I had my settlement near the bottom of Hellas Planitia, the deepest part of Mars.) Accordingly, the major chronic hazard is cosmic radiation, but a sudden strike by a major solar event is also lethal.

There are two types of shielding. The first is active, the use of magnetic or plasma shields, but currently these are theoretical, such as my suggested L1 superconducting magnetic field generator. The second is passive, which is to place matter between the person and the source. At present we are reliant on passive measures. The better materials for stopping such charged particles are those with a high number density of atoms with many electrons per unit mass, which ends up meaning elements of low atomic number. Materials rich in hydrogen such as water or polyethylene perform well, although nothing practical can totally eliminate cosmic radiation.

For settlers on Mars, interactions with the atmosphere lead to neutrons and gamma rays being dominant. Terrain offers protection, thus being adjacent to a cliff will halve the exposure compared with open terrain. The water in regolith will greatly attenuate neutrons with less kinetic energy than 10 MeV. Liquid hydrogen is probably the best, but its extremely low temperature probably makes it impractical. Organic plastics work well; aluminium, which is used in spacecraft, is somewhat less satisfactory, but οn Μars the regolith is probably optimal, because it is already there and hence is cheap. On the other hand, it has to be bound by something, otherwise the wind will blow it away. The article suggests making bricks from regolith. The simplest protection is to live in caves. However, there may be a shortage of caves. People talk about lava tubes, but much of the volcanism on Mars has been around very large volcanoes, or older ones that erupted more in a pyroclastic fashion. They will be short on caves, while settlers are more likely to head for craters, which are not the obvious place to find caves, although rapidly exiting steam might leave one. One place where there might be caves is the Margaritifer Chaos, where there  are signs of massive water outflows from a very small source.

However, living underground does not help plant growth, and the idea of having huge caverns with lights would require a huge investment in lights. It should be easy to make glass that will be opaque to UV radiation and will offer tolerable radiation protection. Silicate uses light atoms and should compare favourably with aluminium. Further, the danger of cosmic rays is largely long-term health; plants for food are not long-lived. One of the main problems for people settling on Mars is the cost and mass of what they have to take with them. Making bricks from regolith is great because regolith is there. The cost of lifting stuff up from Earth and taking it to Mars is huge, so as much as possible has to be made there. That is why lights for the underground growing of food would be very expensive. But the making of any habitat or plant growing area on the surface requires sealing to prevent gas pressure escaping. In my “Red Gold” I suggest one of the very first things that has to be learned is how to make a cement from Martian materials. The ability to make concrete is the first requirement to make the footers of “glass-houses” to grow plants, and cement is necessary to put bricks together. There is an awful lot of detail that has to be addressed because once settlers get there, if they haven’t got something, they cannot go to the corner store and get it.

Betelgeuse Dimmed

First, I apologize for the initial bizarre appearance of my last post. For some reason, some computer decided to slice and dice. I have no idea why, or for that matter, how. Hopefully, this post will have better luck.

Some will recall that around October 2019 the red supergiant Betelgeuse dimmed, specifically from magnitude +0.5 down to +1.64. As a variable star, its brightness oscillates, but it had never dimmed like this before, at least within our records. This generated a certain degree of nervousness or excitement because a significant dimming is probably what happens initially before a supernova. There has been no nearby supernova since that of the crab nebula in 1054 AD.

To put a cool spot into perspective, if Betelgeuse replaced the sun, its size is such it would swallow Mars, and its photosphere might almost reach Saturn. Its mass is estimated at least ten times, or possibly up to twenty times, the mass of the sun. Such a variation sparks my interest because when I pointed out that my proposed dependence of characteristic planetary orbital semimajor axes on the cube of the mass of the star ran into trouble because the stellar masses were not known that well I got criticised by an astronomer: they knew the masses to within a few percent. The difference between ten times the sun’s mass and twenty times is more than a few percent. This is a characteristic of science. They can measure stellar masses fairly accurately in double star systems, then they “carry over” the results,

But back to Betelgeuse. Our best guess as to distance is between 500 – 600 light years. Interestingly, we have observed its photosphere, the outer “shell” of the star that is transparent to photons, at least to a degree, and this is non-spherical, presumably due to stellar pulsations that send matter out from the star. The star may seem “stable” but actually its surface (whatever that means) is extremely turbulent. It is also surrounded by something we could call an atmosphere, an envelope of matter about 250 times the size of the star. We don’t really know its size because these asymmetric pulsations can add several astronomical units (the Earth-sun distance) in selected directions.

Anyway, back to the dimming. Two rival theories were produced: one involved the development of a large cooler cell that came to the surface and was dimmer than the rest of Betelgeuse’s surface. The other was the partial obscuring of the star by a dust cloud. Neither proposition really explained the dimming, nor did they explain why Betelgeuse was back to normal by the end of February, 2020. Rather unsurprisingly, the next proposition was that the dimming was caused by both of those effects.

Perhaps the biggest problem because telescopes could only look at the star sone of them however a Japanese weather satellite ended up providing just the data they needed. This was somewhat inadvertent. The weather satellite was in geostationary orbit 35,786 km above the Western Pacific. It was always looking at half of Earth, and always the same half, but the background was also always constant, and in the background was Betelgeuse. The satellite revealed that the star overall cooled by 140 degrees C. This was sufficient to reduce the heating of a nearby gas cloud, and when it cooled, dust condensed and formed obscuring dust. So both theories were right, and even more strangely, both contributed roughly equally to what was called “the Great Dimming”.

It also suggested more was happening to the atmospheric structure of the star before this happened. By looking at the infrared lines, it became apparent that water molecules in the upper atmosphere that would normally create absorption lines in the star’s spectrum suddenly changed to form emission lines. Something had made them become unexpectedly hotter. The current thinking is that a shock-wave from the interior propelled a lot of gas outwards from the star, leading to a cooler surface, while heating the outer atmosphere. That is regarded as the best current explanation. It is possible that there was a similar dimming event in the 1940s, but otherwise we have not noticed much, but possibly it could have occurred but our detection methods may not have been accurate enough. People may not want to get carried away with, “I think it might be dimmer.” Anyway, for the present, no supernova. But one will occur, probably within the next 100,000 years. Keep looking upwards!

The First Atmosphere

Ι have now published the second edition of my ebook “Planetary Formation and Biogenesis”. It has just under 1290 references, each about a different aspect of the issue, although there is almost certainly a little double counting because references follow chapters, and there will be some scientific papers that are of sufficient importance to be mentioned in two chapters. Nevertheless, there is plenty of material there. The reason for a second edition is that there has been quite a lot of additional; information from the past decade. And, of course, no sooner did I publish than something else came out, so I am going to mention that in this post. In part this is because it exemplifies some of what I think is wrong with modern science. The paper, for those interested, is from Wilcoski et al. Planet Sci J. 3: 99. It is open access so you can read it.

First, the problem it attempts to address: the standard paradigm is that Earth’s atmosphere was initially oxidised, and comprised carbon dioxide and nitrogen. The question then is, when did this eventuate? What we know is the Earth was big enough that if still in the accretion disk it would have had an atmosphere of hydrogen and helium. If it did not accrete until after the disk was expelled, it would have no atmosphere initially, and an atmosphere had to come from some other process. The ebook shows the evidence and in my opinion it probably had the atmosphere of hydrogen. Either way, the accretion disk gets expelled, and assuming our star was the same as others, for the first few hundred million years the star gave off a lot of extremely energetic UV radiation, and that would be sufficient to effectively blow any atmosphere away. So under that scenario, for some number of hundred million years there would be no atmosphere.

There is an opposing option. Shortly after the Moon-forming event, there would be a “Great Bombardment” of massive impactors. There are various theories this would form a magma ocean and there is a huge steam atmosphere, but there is surprisingly little evidence for this, which many hold onto no matter what. The one piece of definite evidence are some zircons from the Jack Hills in Australia, and these are about 4.2 – 4.3 billion years old – the oldest of any rock we have. Some of these zircons show clear evidence that they formed under temperatures not that different from today. In particular, there was water that had oxygen isotope ratios expected of water that had come from rain.

So, let me revisit this paper. The basic concept is that the Earth was bombarded with massive asteroids and the iron core hit the magma ocean, about half of it was sent into the atmosphere (iron boils at 2861 degrees C) where it reacted with water to form hydrogen and ferrous oxide. The hydrogen reacted with nitrogen to form ammonia.

So, what is wrong with that? First, others argue that iron in the magma ocean settles to the core. That, according to them, is why we have a core. Alternatively, others argue if it comes from an asteroid, it emulsifies in the magma. Now we have the iron doing three different kind of things depending on what answer you want. It can do one of them, but not all of them. Should iron vapour get into the atmosphere, it would certainly reduce steam and make hydrogen, but then the hydrogen would not do very much, but rather would be lost to space because of the sun’s UV. The reaction of hydrogen with nitrogen only proceeds to make much ammonia when there is intense pressure. That could happen deep underground. However, in atmospheric pressure at temperatures above the boiling point of iron, ammonia would immediately dissociate and form nitrogen and hydrogen. The next thing that is wrong is that very few asteroids have an iron core. If one did, what would happen to the asteroid when it hit magma? As an experiment, throw ice into water and watch what happens before it tries to reverse its momentum and float (which an asteroid would not do). Basically, the liquid is what gets splashed away. Rock is a very poor conductor of heat, so the asteroid will sink quite deeply into the liquid and will have to melt off the silicates before the iron starts to melt, and then, being denser, it will sink to the core. On top of that it was assumed the atmosphere contained 100 bars of carbon dioxide, and two bars of nitrogen, in other words an atmosphere somewhat similar to that of Venus today. Assuming what was there to get the answer you want is, I suppose, one way of going about things, in a circular sort of way. However, with tidal heating from a very close Moon, such an atmosphere with that much water would never rain, which contradicts the zircon data. What we have is a story that contradicts the very limited physical evidence we have, which has no evidence in favour of it, and was made up to get the answer wanted so they could explain where the chemicals that formed life might have come from. Needless to say, my ebook has a much better account, and has the advantage that no observations contradict it.

Molecular Oxygen in a Comet

There is a pressure, these days, on scientists to be productive. That is fair enough – you don’t want them slacking off in a corner, but a problem arises when this leads to the publication of papers: there are so many of them that nobody can keep up with even a small fraction of them. Worse, many of them do not seem to say much. Up to a point, this has an odd benefit: if you leave a lot unclear, all your associates can publish away and cite you, which has this effect of making you seem more important because funders like to count citations. In short, with obvious exceptions, the less you advance the science, the more important you seem at second level funding. I am going to pick, maybe unfairly, on one paper from Nature Astronomy (https://www.nature.com/articles/s41550-022-01614-1) as an illustration.

One of the most unexpected findings in the coma of comet 67P/Churyumov-Gerasimenko was “a large amount” of molecular oxygen. Something to breathe! Potential space pilots should not get excited; “a large amount” is only large with respect to what they expected, which was none. At the time, this was a surprise to astronomers because molecular oxygen is rather reactive and it is difficult to see why it would be present. Now there is a “breakthrough”: it has been concluded there is not that much oxygen in the comet at all, but this oxygen came from a separate small reservoir. The “clue” came from the molecular oxygen being associated with molecular water when emitted from a warm site. As it got cooler, any oxygen was associated with carbon dioxide or carbon monoxide. Now, you may well wonder what sort of clue that is? My question is, given there is oxygen there, what would you expect? The comet is half water, so when the surface gets warm, it sublimes. When cooler, only gases at that lower temperature get emitted. What is the puzzle?

However, the authors of the paper came to a different conclusion. They decided that there had to be a deep reservoir of oxygen within the comet, and a second reservoir close to the surface that is made of porous frozen water. According to them, oxygen in the core works its way to the surface and gets trapped in the second reservoir. Note that this is an additional proposition to the obvious one that oxygen was trapped in ice near the surface. We knew there was gas trapped in ice that was released with heat, so why postulate multiple reservoirs, other than to get a paper published?

So, where did this oxygen come from? There are two possibilities. The first is it was accreted with the gas from the disk when the comet formed. This is somewhat difficult to accept. Ordinary chemistry suggests that if oxygen molecules were present in the interstellar dust cloud it should react with hydrogen and form water. Maybe that conclusion is somehow wrong, but we can find out. We can estimate the probability by observing the numerous dust clouds from which stars accrete. As far as I am aware, nobody has ever found rich amounts of molecular oxygen in them. The usual practice when you are proposing something unusual is you find some sort of supporting evidence. Seemingly, not this time.

The second possibility is that we know how molecular oxygen could be formed at the surface. High energy photons and solar wind smash water molecules in ice to form hydrogen and hydroxyl radicals. The hydrogen escapes to space but the hydroxyl radicals unite to form hydrogen peroxide or other peroxides or superoxides, which can work their way into the ice. There are a number of other solids that catalyse the degradation of peroxides and superoxides back to oxygen, which would be trapped in the ice, but released when the ice sublimed. So, from the chemist’s point of view there is a fairly ordinary explanation why oxygen might be formed and gather near the surface. From my point of view, Occam’s Razor should apply: you use the simplest explanation unless there is good evidence. I do not see any evidence about the interior of the comet.

Does it matter? From my point of view when someone with some sort of authority/standing says something like this, there is the danger that the next paper will say “X established that . . “  and it becomes almost a gospel. This is especially so when the assertion cannot be easily challenged with evidence as you cannot get inside that comet. Which gives the perverse realization that you need strong evidence to challenge an assertion, but maybe no evidence at all to assert it in the first place. Weird?