Interstellar Travel Opportunities.

As you may have heard, stars move. The only reason we cannot see this is because they are so far away, and it takes so long to make a difference. Currently, the closest star to us is Proxima Centauri, which is part of the Alpha Centauri grouping. It is 4.2 light years away, and if you think that is attractive for an interstellar voyage, just wait a bit. In 28,700 years it will be a whole light year closer. That is a clear saving in travelling time, especially if you do not travel close to light speed.

However, there have been closer encounters. Sholz’s star, which is a binary; a squib of a red dwarf plus a brown dwarf, came within 0.82 light years 78,000 years ago. Our stone age ancestors would probably have been unaware of it, because it is so dim that even when that close it was still a hundred times too dim to be seen by the naked eye. There is one possible exception to that: occasionally red dwarfs periodically emit extremely bright flares, so maybe they would see a star appear from nowhere, then gradually disappear. Such an event might go down in their stories, particularly if something dramatic happened. There is one further possible downside for our ancestors: although it is unclear whether such a squib of a star was big enough, it might have exerted a gravitational effect on the Oort cloud, thus generating a flux of comets coming inwards. That might have been the dramatic event.

That star was too small to do anything to disrupt our solar system, but it is possible that much closer encounters in other solar systems could cause all sorts of chaos, including stealing a planet, or having one stolen. They could certainly disrupt a solar system, and it is possible that some of the so-called star-burning giants were formed in the expected places and were dislodged inwards by such a star. That happens when the dislodged entity has a very elliptical orbit that takes it closer to the star where tidal effects with the star circularise it. That did not happen in our solar system. Of course, it does not take a passing star to do that; if the planets get too big and too close their gravity can do it.

It is possible that a modestly close encounter with a star did have an effect on the outer Kuiper Belt, where objects like Eris seem to be obvious Kuiper Belt Objects, but they are rather far out and have very elliptical orbits. It would be expected that would arise from one or more significant gravitational interactions.

The question then is, if a star passed closely should people take advantage and colonise the new system? Alternatively, would life forms there have the same idea if they were technically advanced? Since if you had the technology to do this, presumably you would also have the technology to know what was there. It is not as if you do not get warning. For example, if you are around in 1.4 million years, Gliese 710 will pass within 10,000 AU of the sun, well within the so-called Oort Cloud. Gliese 710 is about 60% the mass of the sun, which means its gravity could really stir up the comets in the Oort cloud, and our star will do exactly the same for the corresponding cloud of comets in their system. In a really close encounter it is not within the bounds of possibility that planetary bodies could be exchanged. If they were, the exchange would almost certainly lead to a very elliptical orbit, and probably at a great distance. You may have heard of the possibility of a “Planet 9” that is at a considerable distance but with an elliptical orbit has caused highly elliptical orbits in some trans Neptunian objects. Either the planet, if it exists at all, or the elliptical nature of the orbits of bodies like Sedna, could well have arisen from a previous close stellar encounter.

As far as I know, we have not detected planets around this star. That does not mean there are not any because if we do not lie on the equatorial plane of that star we would not see much from eclipsing observations (and remember Kepler only looks at a very small section of the sky, and Gliese 710 is not in the original area examined) and at that distance, any astronomer with our technology there would not see us. Which raises the question, if there were planets there, would we want to swap systems? If you accept the mechanism of how planets form in my ebook “Planetary Formation and Biogenesis”, and if the rates of accretion, after adjusting for stellar mass for both were the same, then any rocky planet in the habitable zone is likely to be the Mars equivalent. It would be much warmer and it may well be much bigger than our Mars, but it would not have plate tectonics because its composition would not permit eclogite to form, which is necessary for pull subduction. With that knowledge, would you go?

Food on Mars

Settlers on Mars will have needs, but the most obvious ones are breathing and eating, and both of these are likely to involve plants. Anyone thinking of going to Mars should think about these, and if you look at science fiction the answers vary. Most simply assume everything is taken care of, which is fair enough for a story. Then there is the occasional story with slightly more detail. Andy Weir’s “The Martian” is simple. He grows potatoes. Living on such a diet would be a little spartan, but his hero had no option, being essentially a Robinson Crusoe without a Man Friday. The oxygen seemed to be a given. The potatoes were grown in what seemed to be a pressurised plastic tent and to get water, he catalytically decomposed hydrazine to make hydrogen and then he burnt that. A plastic tent would not work. The UV radiation would first make the tent opaque so the necessary light would not get in very well, then the plastic would degrade. As for making water, burning hydrazine as it was is sufficient, but better still, would they not put their base where there was ice?

I also have a novel (“Red Gold”) where a settlement tries to get started. Its premise is there is a main settlement with fusion reactors and hence have the energy to make anything, but the main hero is “off on his own” and has to make do with less, but can bring things from the main settlement. He builds giant “glass houses” made with layers of zinc-rich glass that shield the inside from UV radiation. Stellar plasma ejections are diverted by a superconducting magnet at the L1 position between Mars and the sun (proposed years before NASA suggested it) and the hero lives in a cave. That would work well for everything except cosmic radiation, but is that going to be that bad? Initially everyone lives on hydroponically grown microalgae, but the domes permit ordinary crops. The plants grow in treated soil, but as another option a roof is put over a minor crater and water provided (with solar heating from space) in which macroalgae grow and marine microalgae, as well as fish and other species, like prawns. The atmosphere is nitrogen, separated from the Martian atmosphere, and some carbon dioxide, and the plants make oxygen. (There would have to be some oxygen to get started, but plants on Earth grew without oxygen initially.)

Since then there have been other quite dramatic proposals from more official sources that assume a lot of automation to begin with. One of the proposals involves constructing huge greenhouses by covering a crater or valley. (Hey, I suggested that!) but the roof is flat and made of plastic, the plastic being made from polyethylene 2,5-furandicarboxylate, a polyester made from carbohydrates grown by the plants. This is used as a bonding agent to make a concrete from Martian rock. (In my novel, I explained why a cement is very necessary, but there are limited uses.) The big greenhouse model has some limitations. In this, the roof is flat, and in essentially two layers, and in between are vertical stacks of algae growing in water. The extra value here is that water filters out the effect of cosmic rays, although you need several meters of it. Now we have a problem. The idea is that underneath this there is a huge habitat, and for every cubic meter of water, we have one tonne mass, and on Mars, about 0.4 tonne of force on the lower flat deck. If this bottom deck is the opaque concrete, then something bound by plastic adhesion will slip. (Our concrete on bridges is only inorganic, and the binding is chemical, not physical, and further there is steel reinforcing.) Below this there would need to be many weight-bearing pillars. And there would need to be light generation between the decks (to get the algae to grow) and down below. Nuclear power would make this easy. Food can be grown as algae in between decks, or in the ground down below.

As I see it, construction of this would take quite an effort and a huge amount of materials. The concept is the plants could be grown to make the cement to make the habitat, but hold on, where are the initial plants going to grow, and who/what does all the chemical processing? The plan is to have that in place from robots before anyone gets there but I think that is greatly overambitious. In “Red Gold” I had the glass made from regolith processed with the fusion energy. The advantage of glass over this new suggestion is weight; even on Mars with its lower gravity millions of tonnes remains a serious weight. The first people there will have to live somewhat more simply.

Another plan that I have seen involves finding a frozen lake in a crater, and excavating an “under-ice” habitat. No shortage of water, or screening from cosmic rays, but a problem as I see it is said ice will melt from the heat, erode the bottom of the sheet, and eventually it will collapse. Undesirable, that is.

All of these “official” options use artificial lighting. Assuming a nuclear reactor, that is not a problem in itself, although it would be for the settlement under the ice because heat control would be a problem. However, there is more to getting light than generating energy. What gives off the light, and what happens when its lifetime expires? Do you have to have a huge number of spares? Can they be made on Mars?

There is also the problem with heat. In my novel I solved this with mirrors in space focussing more sunlight on selected spots, and of course this provides light to help plants grow, but if you are going to heat from fission power a whole lot more electrical equipment is needed. Many more things to go wrong, and when it could take two years to get a replacement delivered, complicated is what you do not want. It is not going to be that easy.

A Discovery on Mars

Our space programs now seem to be focusing in the increasingly low concentrations or more obscure events, as if this will tell us something special. Recall earlier there was the supposed finding of phosphine in the Venusian atmosphere. Nothing like stirring up controversy because this was taken as a sign of life. As an aside, I wonder how many people actually have ever noticed phosphine anywhere? I have made it in the lab, but that hardly counts. It is not a very common material, and the signal in the Venusian atmosphere was almost certainly due to sulphur dioxide. That in itself is interesting when you ask how would that get there? The answer is surprisingly simple: sulphuric acid is known to be there, and it is denser, and might form a fog or even rain, but as it falls it hits the hotter regions near the surface and pyrolysis to form sulphur dioxide, oxygen and water. These rise, the oxygen reacts with sulphur dioxide to make sulphur trioxide (probably helped by solar radiation), which in turn reacts with water to form sulphuric acid, which in turn is why the acid stays in the atmosphere. Things that have a stable level on a planet often have a cycle.

In February this year, as reported in Physics World, a Russian space probe detected hydrogen chloride in the atmosphere of Mars after a dust storm occurred. This was done with a spectrometer that looked at sunlight as it passed through the atmosphere, and materials such as hydrogen chloride would be picked up as a darkened line at the frequency for the bond vibration in the infrared part of the spectrum. The single line, while broadened due to rotational options, would be fairly conclusive. I found the article to be interesting for all sorts of reasons, one of which was for stating the obvious. Thus it stated that dust density was amplified in the atmosphere during a global dust storm. Who would have guessed that? 

Then with no further explanation, the hydrogen chloride could be generated by water vapour interacting with the dust grains. Really? As a chemist my guess would be that the dust had wet salt on it. UV radiation and atmospheric water vapour would oxidise that, to make at first sodium hypochlorite, like domestic bleach and then hydrogen.  From the general acidity we would then get hydrogen chloride and probably sodium carbonate dust. They were then puzzled as to how the hydrogen chloride disappeared. The obvious answer is that hydrogen chloride would strongly attract water, which would form hydrochloric acid, and that would react with any oxide or carbonate in the dust to make chloride salts. If that sounds circular, yes it is, but there is a net degradation of water; oxygen or oxides would be formed, and hydrogen would be lost to space. The loss would not be very great, of course, because we are talking about parts per billion in a highly rarefied upper atmosphere and only during a dust storm.

Hydrogen chloride would also be emitted during volcanic eruptions, but that is probably able to be eliminated here because Mars no longer has volcanic eruptions. Fumarole emissions would be too wet to get to the upper atmosphere, and if they occurred, and there is no evidence they still do, any hydrochloric acid would be expected to react with oxides, such as the iron oxide that makes Mars look red, rather quickly.  So the unfortunate effect is that the space program is running up against the law of diminishing returns. We are getting more and more information that involves ever-decreasing levels of importance. Rutherford once claimed that physics was the only science – the rest was stamp collecting.  Well, he can turn in his grave because to me this is rather expensive stamp collecting.

Living Near Ceres

Some will have heard of Gerard O’Neill’s book, “The High Frontier”. If not, see https://en.wikipedia.org/wiki/The_High_Frontier:_Human_Colonies_in_Space. The idea was to throw material up from the surface of the Moon to make giant cylinders that would get artificial gravity from rotation, and people could live their lives in the interior with energy being obtained in part by solar energy. The concept was partly employed in the TV series “Babylon 5”, but the original concept was to have open farmland as well. Looks like science fiction, you say, and in fairness I have included such a proposition in a science fiction novel I am currently writing, However, I have also read a scientific paper on this topic (arXiv:2011.07487v3) which appears to have been posted on the 14th January, 2021. The concept is to put such a space settlement using material obtained from the asteroid Ceres, and orbiting near Ceres.

The proposal is ambitious, if nothing else. The idea is to build a number of habitats, and to ensure such habitats are not too big but they stay together they are tethered to a megasatellite, which in turn will grow and new settlements are built. The habitats spin in such a way to attain a “gravity” of 1 g, and are attached to their tethers by magnetic bearings that have no physical contact between faces, and hence never wear. A system of travel between habitats proceeds along the tethers. Rockets would be unsustainable because the molecules they throw out to space would be lost forever.

The habitats would have a radius of 1 km, a length of 10 km, and have a population of 56,700, with 2,000 square meters per person, just under 45% of which would be urban. Slightly more scary would be the fact it has to rotate every 1.06 minutes. The total mass per person would be just under 10,000 t, requiring an energy to produce it of 1 MJ/kg, or about 10 GJ.

The design aims to produce an environment for the settlers that has Earth-like radiation shielding, gravity, and atmosphere. It will have day/night on a 24 hr cycle with 130 W/m^2 insolation, similar to southern Germany, and a population density of 500/km^2, similar to the Netherlands. There would be fields, parks, and forests, no adverse weather, no natural disasters and ultimately it could have a greater living area than Earth. It will be long-term sustainable. To achieve that, animals, birds and insects will be present, i.e.  a proper ecosystem. Ultimately it could provide more living area than Earth. As can be seen, that is ambitious. The radiation shielding involves 7600 kg/m^2, of which 20% is water and the rest silicate regolith. The rural spaces have a 1.5 m depth of soil, which is illuminated by the sunlight. The sunlight is collected and delivered from mirrors into light guides. Ceres is 2.77 times as far as Earth from the sun, which means the sunlight is only about 13% as strong as at Earth, so over eight times the mirror collecting are is required for every unit area to be illuminated to get equivalent energy. 

The reason cited for proposing this to be at Ceres is that Ceres has nitrogen. Actually, there are other carbonaceous asteroids, and one that is at least 100 km in size could be suitable. Because Ceres’ gravity is 0.029 times that of Earth, a space elevator could be feasible to bring material cheaply from the dwarf planet, while a settlement 100,000 km from the surface would be expected to have a stable orbit.

In principle, there could be any number of these habitats, all linked together. You could have more people living there than on Earth. Of course there are some issues with the calculation. The tethering of habitats, and of giving the habitats sufficient strength requires about 5% of the total mass in the form of steel. Where does the iron come from? The asteroids have plenty of iron, but the form is important. How will it be refined? If it is on the form of olivine or pyroxene, then with difficulty. Vesta apparently has an iron core, but Vesta is not close, and most of the time, because it has a different orbital period, it is very far away.But the real question is, would you want to live in such a place? How much would you pay for the privilege? The cost of all this was not estimated, but it would be enormous so most people could not afford it. In my opinion, cost alone is sufficient that this idea will not see the light of day.

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.

The Fermi Paradox: Where are the Aliens?

This question, as much as anything, illustrates why people have trouble thinking through problems when they cannot put their own self-importance to one side. Let us look at this problem not from our point of view.

The Fermi paradox is a statement that since there are so many stars, most of which probably have planets, and a reasonable number of them have life, more than half of those are likely to have been around longer than us and so should be more technically advanced, but we have seen no clue as to their presence. Why not? That question begs the obvious counter: why should we? First, while the number of planets is huge, most of them are in other galaxies, and of those in the Milky Way, stars are very well-separated. The nearest, Alpha Centauri, is a three star system: two rather close stars (A G-type star like our sun and a K1 star) and a more distant red dwarf, and these are 4.37 light years away. The two have distances that vary between 35.6 AU to 11.2 AU, i.e. on closest approach they come a little further apart than Saturn and the sun.  That close approach means that planets corresponding to our giants could not exist in stable orbits, and astronomers are fairly confident there are no giants closer to the star. Proxima Centauri has one planet in the habitable zone, but for those familiar with my ebook “Planetary Formation and Biogenesis” will know that in my opinion, the prospect for life originating there, or around most Red Dwarfs, is extremely low. So, could there be Earth-like planets around the two larger stars? Maybe, but our technology cannot find them. As it happens, if there were aliens there, they could not detect Earth with technology at our level either.  Since most stars are immensely further away, rocky planets are difficult to discover. We have found exoplanets, but they are generally giants, planets around M stars, or planets that inadvertently have their orbital planes aligned so we can see eclipses.

This is relevant, because if we are seeking a signal from another civilization, as Seti seeks, then either the signal is deliberate or accidental. An example of accidental is the electromagnetic radiation we send into space through radio and TV signals. According to tvtechnology.com “An average large transmitter transmits about 8kW per multiplex.” That will give “acceptable signal strength” over, say, 50 km. The signal strength attenuates according to the square of the distance, so while the signals will get to Alpha Centauri, they will be extremely weak, and because of bandwidth issues, broadcasts from well separated transmitters will interfere with each other. Weak signals can be amplified, but aliens at Alpha Centauri would get extremely faint noise that might be assignable to technology. 

Suppose you want to send a deliberate signal? Now, you want to boost the power, and the easiest way to get over the inverse square attenuation is to focus the signal. Now, however, you need to know exactly where the intended recipient will be. You might do this for one of your space ships, in which case you would send a slightly broader signal on a very high power level at an agreed frequency but as a short burst. To accidentally detect this, because you have a huge range of frequencies to monitor, you have to accidentally be on that frequency at the time of the burst. There is some chance of Seti detecting such a signal if the space ship was heading to Earth, but then why listen for such a signal, as opposed to waiting for the ship.

The next possible deliberate signal would be aimed at us. To do that, they would need to know we had potential, but let us suppose they did. Suppose it takes something like 4.5 billion years to get technological life, and at that nice round number, they peppered Earth with signals. Oops! We are still in the Cretaceous. Such a move would require a huge power output so as to flood whatever we were using, a guess as to what frequencies we would find of interest, and big costs. Why would they do that, when it may take hundreds or thousands of years for a response? It makes little sense for any “person” to go to all that trouble and know they could never know whether it worked or not. We take the cheap option of listening with telescopes, but if everyone is listening, nobody is sending.

How do they choose a planet? My “Planetary Formation and Biogenesis” concludes you need a rocky planet with major felsic deposits, which is most probable around the G type star (but still much less than 50% of them). So you would need some composition data, and in principle you can get that from spectroscopy (but with much better technology than we have). What could you possibly see? Oxygen is obvious, except it gives poor signals. In the infrared spectra, you might detect ozone, and that would be definitive. You often see statements that methane should be detectable. Yes, but Titan has methane and no life. Very low levels of carbon dioxide is a strong indication, as it suggests large amounts of water to fix it, and plate tectonics to renew it. Obviously, signals from chlorophyll would be proof, but they are not exactly strong. So if they are at anything but the very closest stars they would not know whether we are here, so why waste that expense. The Government accountants would never fund such a project with such a low probability of getting a return on investment. Finally, suppose you decided a planet might have technology, why would you send a signal? As Hawking remarked, an alien species might decide this would be a good planet to eradicate all life and transform it suitable for the aliens to settle. You say that is unlikely, but with all those planets, it only needs one such race. So simple game theory suggests “Don’t do it!” If we assume they are more intelligent than us, they won’t transmit because there is no benefit for those transmitting.

The Apollo Program – More Memories from Fifty Years Ago.

As most will know, it is fifty years ago since the first Moon landing. I was doing a post-doc in Australia at the time, and instead of doing any work that morning, when the word got around on that fateful day we all downed tools and headed to anyone with a TV set. The Parkes radio telescope had allowed what they received to be live-streamed to Australian TV stations. This was genuine reality TV. Leaving aside the set picture resolution, we were seeing what Houston was seeing, at exactly the same time. There was the Moon, in brilliant grey, and we could watch the terrain get better defined as the lander approached, then at some point it seemed as if the on-board computer crashed. (As computers go, it was primitive. A few years later I purchased a handheld calculator that would leave that computer for dead in processing power.) Anyway, Armstrong took control, and there was real tension amongst the viewers in that room because we all knew if anything else went wrong, those guys would be dead. There was no possible rescue. The ground got closer, Armstrong could not fix on a landing site, the fuel supply was getting lower, then, with little choice because of the fuel, the ground got closer faster, the velocity dropped, and to everyone’s relief the Eagle landed and stayed upright. Armstrong was clearly an excellent pilot with excellent nerves. Fortunately, the lander’s legs did not drop into a hole, and as far as we could tell, Armstrong chose a good site. Light relief somewhat later in the day to watch them bounce around on the lunar surface. (I think they were ordered to take a 4-hour rest. Why they hadn’t rested before trying to land I don’t know. I don’t know about you, but if I had just successfully landed on the Moon, and would be there for not very long, a four-hour rest would not seem desirable.)

In some ways that was one of America’s finest moments. The average person probably has no idea how much difficult engineering went into that, and how everything had to go right. This was followed up by six further successful landings, and the ill-fated Apollo 13, which nevertheless was a triumph in a different way in that despite a near-catastrophic situation, the astronauts returned to Earth.

According to the NASA website, the objectives of the Apollo program were:

  • Establishing the technology to meet other national interests in space.
  • Achieving preeminence in space for the United States.
  • Carrying out a program of scientific exploration of the Moon.
  • Developing human capability to work in the lunar environment.

The first two appear to have been met, but obviously there is an element of opinion there. It is debatable that the last one achieved much because there has been no effort to return to the Moon or to use it in any way, although that may well change now. Charles Duke turns 84 this year and he still claims the title of “youngest person to walk on the Moon”.

So how successful was the scientific program? In some ways, remarkably, yet in others there is a surprising reluctance to notice the significance of what was found. The astronauts brought back a large amount of lunar rocks, but there were some difficulties here in that until Apollo 17, the samples were collected by astronauts with no particular geological training. Apollo 17 changed that, but it was still one site, albeit with a remarkably varied geological variety. Of course, they did their best and selected for variety, but we do not know what was overlooked.

Perhaps the most fundamental discovery was that the isotopes from lunar rocks are essentially equivalent to earth rocks, and that means they came from the same place. To put this in context, the ratio of isotopes of oxygen, 16O/17O/18O varies in bodies seemingly according to distance from the star, although this cannot easily be represented as a function. The usual interpretation is that the Moon was formed when a small planet, maybe up to the size of Mars, called Theia crashed into Earth and sent a deluge of matter into space at a temperature well over ten thousand degrees Centigrade, and some of this eventually aggregated into the Moon. Mathematical modelling has some success at showing how this happened, but I for one am far from convinced. One of the big advantages of this scenario is that it shows why the Moon has no significant water, no atmosphere, and never had any, apart from some water and other volatiles frozen in deep craters at the South Pole that almost certainly arrived from comets and condensed there thanks to the cold. As an aside, you will often read that the lunar gravity is too weak to hold air. That is not exactly true; it cannot hold it indefinitely, but if it started with carbon dioxide proportional in mass, or even better in cross-sectional area, to what Earth has, it would still have an atmosphere.

One of the biggest disadvantages of this scenario is where did Theia come from? The models show that if the collision, which happened about 60 million years after the Earth formed, occurred from Theia having a velocity much above the escape velocity from Earth, the Moon cannot form. It gets the escape velocity from falling down the Earth’s gravitational field, but if it started far enough further out that would have permitted Theia to have lasted 60 million years, then its velocity would be increased by falling down the solar gravitational field, and that would be enhanced by the eccentricity of its trajectory (needed to collide). Then there is the question of why are the isotopes the same as on Earth when the models show that most of the Moon came from Theia. There has been one neat alternative: Theia accreted at the Earth-Sun fourth or fifth Lagrange point, which gives it indefinite stability as long as it is small. That Theia might have grown just too big to stay there explains why it took so long and starting at the same radial distance as Earth explains why the isotope ratios are the same.

So why did the missions stop? In part, the cost, but that is not a primary reason because most of the costs were already paid: the rockets had already been manufactured, the infrastructure was there and the astronauts had been trained. In my opinion, it was two-fold. First, the public no longer cared, and second, as far as science was concerned, all the easy stuff had been done. They had brought back rocks, and they had done some other experiments. There was nothing further to do that was original. This program had been a politically inspired race, the race was run, let’s find something more exciting. That eventually led to the shuttle program, which was supposed to be cheap but ended up being hideously expensive. There were also the deep space probes, and they were remarkably successful.

So overall? In my opinion, the Apollo program was an incredible technological program, bearing in mind from where it started. It established the US as firmly the leading scientific and engineering centre on Earth, at least at the time. Also, it got where it did because of a huge budget dedicated to one task. As for the science, more on that later.

Earth’s Twin: Venus

Leaving aside the Moon and the Sun, Venus is the brightest object in the sky, and at times the closest. Further, Venus is the only planet that is comparable to Earth; its mass is about 81.5%, its size is about 95%, and its gravity is about 90.5% that of Earth. The orbit of Venus has only 1/3 of Earth’s eccentricity, and while Earth has an axial tilt of 23.5 degrees (which results in right now I am embedded in winter and many of the readers will be enjoying a pleasant summer, or maybe a heat wave) Venus has a tilt of only 2.6 degrees. That means that Venus has a more or less uniform temperature and no seasons. At first sight, that would make it an attractive target for space probes, but while NASA has sent eleven orbiters and eight landers to Mars, it has only sent two orbiters to Venus. Why the lack? Not for lack of interest since from 1990 NASA has considered nearly thirty proposals, but it approved none. The dead hand of the committee strikes again. The reason is that Venus, up close, is strangely unattractive.

The first problem is atmospheric pressure, which is about 90 bar over most of the planet, and it has an average surface temperature of about 460 degrees C but this can vary by +160 degrees C. The second problem is the nature of the atmosphere. Most of it is carbon dioxide. Venus also has about four times the amount of nitrogen than Earth has, and all of that is relatively harmless. What is less harmless is the atmosphere has clouds of sulphuric acid, together with hydrogen chloride and hydrogen fluoride. Hydrogen fluoride is particularly nasty, because it reacts with glass, and while the sulphuric acid will attack all the basic electronics, etc, the hydrogen fluoride will attack lenses. Very shortly, photography, or seeing where a rover is going, will no longer be possible. And, of course, if it can survive, the heat soon kills it. The first lander to return data was Venera 7, a 1970 Soviet lander that survived for 23 minutes. In 1975, Venera 9 sent back the first pictures from the surface, but it too did not last very long. Funding committees do not encourage very expensive rovers with a very short life.

This may change. NASA is designing a “station” that should last at least sixty days, and operate at the ambient temperature. The electronics would be made of silicon carbide, a substance that conducts electricity and melts somewhere above 2,800 degrees C. No danger of that melting, although all the metals in the craft would have to be resistant to the ambient heat and the corrosion. Titanium would probably manage reasonably well. So maybe we shall get to know more about the planet.

There have apparently been proposals to “colonise” Venus through “settlements” floating above the cloud levels, i.e.presumably some ship-like structure supported by gigantic balloons. Personally, I feel this is unreal. The total weight must displace an equal weight of gas, and the idea is to get above the clouds. Up there, the gas is nowhere near as dense (the pressure is only about half that 90 bar at the top of the highest mountain) and to go higher the pressure really drops away. So to support sufficient mass you would need very large balloons, made of what? Any fabric or rubber would be broken down by the solar UV at that height. Metals would corrode. And what would the gas be? The obvious ones would be hydrogen and helium (no danger of fire because there is no air) but these gases leak like crazy. You may think you can hold it, but for centuries? Then there is another minor problem: at the top of the atmosphere winds can reach several hundred kilometres per hour.

So what is “wrong” with Venus, from our point of view? There are two things. The first is the very slow rotation, which happens to be retrograde. The direction is not so much a problem, but the slowness is. However, the main one is, no significant water. If Venus had the amount of water Earth has, it would have fixed all that carbon dioxide as limestone or dolomite, in which case the atmospheric pressure would be about 3 times our atmosphere (because it has four times the amount of nitrogen). If we wanted to have breathable air, we would have to add another atmosphere of oxygen.

So in theory we could terraform Venus. At the expense of much energy what we would have to do is bring in a number of Kuiper Belt objects, or maybe cometary material from around Jupiter would be better because they contain much less additional nitrogen and carbon monoxide, and make them hit Venus, preferably on the side in a way that the angular momentum of the incoming object was added to the current Venusian rotation, in other words, spin it up. Give it water, and chemistry would do the rest, although it would probably also be preferable to cool it by shading it from the sun at least to some extent. Yes, the temperatures would still be high, but as long as it can cool to 300 degrees C, the pressure will ensure there is some liquid, and the fixing of the gas will start, and initiate positive feedback

Suppose we could give Venus as much water as Earth, then the planet would be more like a water world. It is an interesting question whether Venus has any felsic/granitic material. This is the stuff that makes continents. The great bulk of the material on any rocky planet is basaltic, which in turn is because the oxides of silicon, magnesium and iron are the most commonly available rock-forming materials. Aluminium, as an element, is over an order of magnitude less common than silicon, which it replaces in aluminosilicates. Being less dense than basalt, granite floats on the basalt, provided it can separate itself from the basalt. In my ebook “Planetary Formation and Biogenesis”, I propose that the separation essentially has to take place prior to and during planetary formation. Venus does have two minicontinents: Ishtar and Aphrodite Terrae.

The actual differentiation of the planet, when the granite moves from the deep and comes out on the surface occurs slowly (the small amounts of plagioclase on Mars apparently took about two billion years.) and the rate probably depends on the amount actually accreted. The evidence is that on Earth very large amounts erupted in massive pulses. In the absence of such granite, a large planet will be rather flat, apart from some volcanic peaks.

There would still be a problem in that Venus has no plate tectonics. They are needed to provide the recycling of carbon dioxide, as eventually if the lot were fixed, any life would presumably die. We don’t know what starts plate tectonics. One possibility is the presence of granitic continents, another is the forces arising from rotational motion.  It is just possible they could start if there were more rotational motion, but we don’t know. All in all, not an attractive planet in detail, so maybe we should look after our own better.

The Ice Giants’ Magnetism

One interesting measurement made from NASA’S sole flyby of Uranus and Neptune is that they have complicated magnetic fields, and seemingly not the simple dipolar field as found on Earth. The puzzle then is, what causes this? One possible answer is ice.

You will probably consider ice as not particularly magnetic nor particularly good at conducting electric current, and you would be right with the ice you usually see. However, there is more than one form of ice. As far back as 1912, the American physicist Percy Bridgman discovered five solid phases of water, which were obtained by applying pressure to the ice. One of the unusual properties of ice is that as you add pressure, the ice melts because the triple point (the temperature where solid, liquid and gas are in equilibrium) is at a lower temperature than the melting point of ice at room pressure (which is 0.1 MPa. A pascal is a rather small unit of pressure; the M mean million, G would mean billion). So add pressure and it melts, which is why ice skates work. Ices II, III and V need 200 to 600 MPa of pressure to form. Interestingly, as you increase the pressure, Ice III forms at about 200 Mpa, and at about -22 degrees C, but then the melting point rises with extra pressure, and at 350 MPa, it switches to Ice V, which melts at – 18 degrees C, and if the pressure is increased to 632.4 MPa, the melting point is 0.16 degrees C. At 2,100 MPa, ice VI melts at just under 82 degrees C. Skates don’t work on these higher ices. As an aside, Ice II does not exist in the presence of liquid, and I have no idea what happened to Ice IV, but my guess is it was a mistake.

As you increase the pressure on ice VI the melting point increases, and sooner or later you expect perhaps another phase, or even more. Well, there are more, so let me jump to the latest: ice XVIII. The Lawrence Livermore National Laboratory has produced this by compressing water to 100 to 400 GPa (1 to 4 million times atmospheric pressure) at temperatures of 2,000 to 3,000 degrees K (0 degrees centigrade is about 273 degrees K, and the scale is the same) to produce what they call superionic ice. What happens is the protons from the hydroxyl groups of water become free and they can diffuse through the empty sites of the oxygen lattice, with the result that the ice starts to conduct electricity almost as well as a metal, but instead of moving electrons around, as happens in metals, it is assumed that it is the protons that move.

These temperatures and pressures were reached by placing a very thin layer of water between two diamond disks, following which six very high power lasers generated a sequence of shock waves that heated and pressurised the water. They deduced what they got by firing 16 additional high powered lasers that delivered 8 kJ of energy in a  one-nanosecond burst on a tiny spot on a small piece of iron foil two centimeters away from the water a few billionths of a second after the shock waves. This generated Xrays, and from the way they diffracted off the water sample they could work out what they generated. This in itself is difficult enough because they would also get a pattern from the diamond, which they would have to subtract.

The important point is that this ice conducts electricity, and is a possible source of the magnetic fields of Uranus and Neptune, which are rather odd. For Earth, Jupiter and Saturn, the magnetic poles are reasonably close to the rotational poles, and we think the magnetism arises from electrically conducting liquids rotating with the planet’s rotation. But Uranus and Neptune have quite odd magnetic fields. The field for Uranus is aligned at 60 degrees to the rotational axis, while that for Neptune is aligned at 46 degrees to the rotational axis. But even odder, the axes of the magnetic fields of each do not go through the centre of the planet, and are displaced quite significantly from it.

The structure of these planets is believed to be, from outside inwards, first an atmosphere of hydrogen and helium, then a mantle of water, ammonia and methane ices, then interior to that a core of rock. My personal view is that there will also be carbon monoxide and nitrogen ices in the mantle, at least of Neptune. The usual explanation for the magnetism has been that magnetic fields are generated by local events in the icy mantles, and you see comments that the fields may be due to high concentrations of ammonia, which readily forms charged species. Such charges would produce magnetic fields due to the rapid rotation of the planets. This new ice is an additional possibility, and it is not beyond the realms of possibility that it might contribute to the other giants.

Jupiter is found from our spectroscopic analyses to be rather deficient in oxygen, and this is explained as being due to the water condensing out as ice. The fact that these ices form at such high temperatures is a good reason to believe there may be such layers of ice. This superionic ice is stable as a solid at 3000 degrees K, and that upper figure simply represents the highest temperature the equipment could stand. (Since water reacts with carbon, I am surprised it got that high.) So if there were a layer of such ice around Jupiter’s core, it too might contribute to the magnetism. Whatever else Jupiter lacks down there, pressure is not one of them.

Asteroid (101955) Bennu

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

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

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

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

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

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

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

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