Some Unanswered Questions from the Lunar Rocks

In the previous post I hinted that some of what we found from our study of moon rocks raises issues of self-consistency when viewed in terms of the standard paradigm. To summarize the relevant points of that paradigm, the argument goes that the dust in the accretion disk that was left behind after the star formed accreted into Mars-sized bodies that we shall call embryos, and these moved around in highly elliptical orbits and eventually collided to form planets. While these were all mixed up – simulations suggest what made Earth included bodies from outside Mars’ current orbit, and closer to the star than Mercury’s current orbit. These collisions were extraordinarily violent, and the Earth formed from a cloud of silicate vapours that condensed to a ball of boiling silicates at a little under 3000 degrees C. Metallic iron boils at 2862 degrees C, so it was effectively refluxing, and under these conditions it would extract elements such as tungsten and gold that dissolve in iron and take them with it to the core. About sixty million years after Earth formed, one remaining embryo struck Earth, a huge amount of silicates were sent into space, and the Moon condensed from this. The core of this embryo was supposedly iron, and it migrated into the Earth to join our core, leaving the Moon a ball of silicate vapour that had originated from Earth and condensed from something like 10,000 degrees C. You may now see a minor problem for Earth: if this iron took out all the gold, tungsten, etc, how come we can find it? One possibility is the metals formed chemical compounds. That is unlikely because at those temperatures elements that form only moderate-strength chemical bonds would not survive, and since gold is remarkably unreactive, that explanation won’t work. Another problem is that the Moon has very little water and no nitrogen. This easily explained through their being lost to space from the silicate vapours, but where did the Earth get its volatiles? And if the Moon did condense from such high temperatures, the last silicate to condense would be fayalite, but that was not included in the Apollo rocks, or if it were, nothing was made of that. This alone is not necessarily indicative, though, because fayalite is denser than the other olivines, and if there were liquid silicates for long enough it would presumably sink.

The standard paradigm invokes what is called “the late veneer”; after everything was over, Earth got bombarded with carbonaceous asteroids, which contain water, nitrogen, and some of these otherwise awkward metals. It is now that we enter one of the less endearing aspects of modern science: everything tends to be compartmentalised, and the little sub-disciplines all adhere to the paradigm and add small findings that support their view, even if they do not do so particularly well, and there is a reluctance to look at the overall picture. The net result is that while many of the findings can be made to seemingly provide answers to their isolated problems, there is an overall problem with self-consistency. Further, clues that the fundamental proposition might be wrong are carefully shelved.

The first problem was noted at the beginning of the century: the isotope ratios of metals like osmium from such chondrites are different from our osmium. There are various hand-waving argument to the extent that it could just manage if it were mixed with enough of our mantle, but leaving whether the maths are right aside, nobody seems to have noticed the only reason we are postulating this late veneer is that originally the iron stripped all the osmium from the mantle. You cannot dilute A with B if B is not there. There are a number of other reasons, one of which is the nitrogen of such chondrites has more 15N than our nitrogen. Another is to get the amounts of material here we need a huge amount of carbonaceous asteroids, but they have to come through the ordinary asteroids without perturbing them. That takes some believing.

But there is worse. All the rocks found by the Apollo program have none of the required materials and none of the asteroidal isotope signatures. The argument seems to be, they “bounced off” the Moon. But the Moon also has some fairly ferocious craters, so why did the impactors that caused them not bounce off? Let’s suppose they did bounce off, but they did not bounce off the Earth (because the only reason we argue for this is that we need them, so it is said, to account for our supply of certain metals). Now the isotope ratios of the oxygen atoms on the Moon have a value, and that value is constant over rocks that come from deep within the Moon, thanks to volcanism, and for the rocks from the highlands, so that is a lunar value. How can that be the same as Earth’s if Earth subsequently got heavily bombarded with asteroids that we know have different values? My answer, in my ebook “Planetary Formation and Biogenesis” is simple: there were no embryo impacts in forming Earth therefore the iron vapours did not extract out the heavy elements, and there were no significant number asteroid impacts. Almost everything came here when Earth accreted, and while there have been impacts, they made a trivial contribution to Earth’s supply of matter.

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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.

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.

Marsquakes

One of the more interesting aspects of the latest NASA landing on Mars is that the rover has dug into the surface, inserted a seismometer, and is looking for marsquakes. On Earth, earthquakes are fairly common, especially where I live, and they are generated through the fact that our continents are gigantic lumps of rock moving around over the mantle. They can slide past each other or pull themselves down under another plate, to disappear deep into the mantle, while at other places, new rock emerges to take their place, such as at the mid-Atlantic ridge. Apparently the edges of these plates move about 5 – 10 cm each year. You probably do not notice this because the topsoil, by and large, does not move with the underlying crust. However, every now and again these plates lock and stop moving there. The problem is, the rest of the rock is moving, so considerable strain energy is built up, the lock gives way, very large amounts of energy are released, and the rock moves, sometimes be several meters. The energy is given out as waves, similar in many ways as sound waves, through the rock. If you see waves in the sea, you will note that while the water itself stays more or less in the same place on average, in detail something on the surface, like a surfer, goes up and down, and in fact describes what is essentially a circle if far enough out. Earthquake waves do the same thing. The rock moves, and the shaking can be quite violent. Of course, the rock moves where the actual event occurred, and sometimes the waves trigger a further shift somewhere else.

Such waves travel out in all directions through the rock. Now another feature of all waves is that when they strike a medium through which they will travel with a different velocity, they undergo partial reflection and refraction. There is an angle of incidence when only reflection occurs, and of course, on a curved surface, the reflected waves start spreading as the angles of incidence vary. A second point is that the bigger the difference in wave speed between the two media, the more reflection there is. On Earth, this has permitted us to gather information on what is going on inside the Earth. Of course Earth has some big advantages. We can record seismic events from a number of different places, and even then the results are difficult to interpret.

The problem for Mars is there will be one seismometer that will measure wave frequency, amplitude, and the timing. The timing will give a good picture of the route taken by various waves. Thus the wave that is reflected off the core will come back much sooner than the wave that travels light through and is reflected off the other side, but it will have the same frequency pattern on arrival, so from such patterns and timing you can sort out, at least in principle, what route they took and from the reflection/refraction intensities, what different materials they passed through. It is like a CT scan of the planet. There are further complications because wave interference can spoil patterns, but waves are interesting that they only create that effect at the site where they interfere. Otherwise, they pass right through other waves and are unchanged when they emerge, apart from intensity changes if energy was absorbed by the medium. There is an obvious problem in that with only one seismometer it is much harder to work out where the source was but the scientists believe over the lifetime of the rover they will detect at least a couple of dozen quakes.

Which gets to the question, why do we expect quakes? Mars does not have plate tectonics, possibly because its high level of iron oxide means eclogite cannot form, and it is thought that the unusually high density of eclogite leads to pull subduction. Accordingly the absence of plate tectonics means we expect marsquakes to be of rather low amplitude. However, minor amplitude quakes are expected. One reason is that as the planet cools, there is contraction in volume. Accordingly, the crust becomes less well supported and tends to slip. A second cause could be magma moving below the surface. We know that Mars has a hot interior, thanks to nuclear decay going on inside, and while Mars will be cooler than Earth, the centre is thought to be only about 200 Centigrade degrees cooler than Earth’s centre. While Earth generates more heat, it also loses more through geothermal emissions. Finally, when meteors strike, they also generate shockwaves. Of course the amplitude of these waves is tiny compared with that of even modest earthquakes.

It is hard to know what we shall learn. The reliance on only one seismometer means the loss of directional analysis, and the origin of the quake will be unknown, unless it is possible to time reflections from various places. Thus if you get one isolated event, every wave that comes must have originated from that source, so from the various delays, paths can be assigned. The problem with this is that low energy events might not generate enough reflections of sufficient amplitude to be detected. The ideal method, of course, is to set off some very large explosions at known sites, but it is rather difficult to do that from here.

What do we expect? This is a bit of guesswork, but for me we believe the crust is fairly thick, so we would expect about 60 km of solid basalt. If we get significantly different amounts, this would mean we would have to adjust our thoughts on the Martian thermonuclear reactions. I expect a rather tiny (for a planet) iron core, the clue here being the overall density of Mars is 3.8, its surface is made of basalt, and basalt has a density of 3.1 – 3.8. There just is not room for a lot of iron in the form of the metal. It is what is in between that is of interest. Comments from some of the scientists say they think they will get clues on planetary formation, which could come from deep structures. Thus if planets really formed from the combination of planetesimals, which are objects of asteroid, size, then maybe we shall see the remains in the form of large objects of different sonic impedance. On the other hand, the major shocks to the system by events such as the Hellas impactor may mean that asymmetries were introduced by such shock waves melting parts. My guess is the observations will not be unambiguous in terms of their meaning, and it will be interesting to see how many different scenarios are considered.

More on M 87

In my post regarding the M 87 black hole, I stated that you do not necessarily know what the black hole and its environs look like from that image. The popular image that seems to have taken over the web is just plain misleading because it focuses on radio waves very close to the event horizon. Katherine Bouma, who developed the algorithm that made the picture possible, explained that there were “an infinite number of possible images” that could explain the data, in part due to atmospheric disturbances of different kinds at widely dispersed sites, while the difficulty in getting good data intensity meant that there was an inherent uncertainty. On the other hand, the hole and the ring were valid. However, there is more that the black hole effects.

There is another image obtained from the Chandra X-ray telescope of the environs of the M 87 black hole You will see somewhere near the middle a small black dot that on closer investigation appears to be shaped like a cross. X marks the spot! This is exactly the case. The black hole, the radius of which is almost five times the distance from the sun to Pluto, is too small to register on this image. And whereas the first image was based on radio waves, this is recording x-rays.

Chandra2

As you can see, the effect covers a monstrous volume.

Why Xrays? This is because of the huge amount of energy being lost during a radiation event. To illustrate, a red dwarf star largely emits infrared radiation, and only a relatively low fraction is in the visible wavelength electromagnetic spectrum. Thus Proxima Centauri, which has a surface temperature of about 3,000 degrees K, puts out 85% of its emissions in the infrared spectrum (although flares do contribute some xrays) and its visible emissions are only 0.0056% as luminous as the sun (which has a surface temperature of about 5772 degrees K. Now, consider that five times the distance from the sun to Pluto does not really register on that image, this will give some indication of the power of the black hole. Those xrays are generated from the energy  given off by dust heating as they fall into the regions of the black hole and give off the extraordinary energy of an xray in the spectrum.

The dust accelerates, gets hotter than the surface of most stars as a consequance of collisions, and eventually becomes a plasma that is orbiting the black hole at relativistic speeds.  As an aside, this shows that the science fiction plots of a space ship suddenly coming across a lurking black hole is somewhat improbable. Observation should give good clues well in advance as the size of the Xray emissions around this one is comparable to the distance of most of the farthest stars we can see with the naked eye.

One of the most bizarre things about black holes is that sometimes you can see a jet of material travelling at relativistic speeds away from the polar regions of the black hole. The jets show only a few degrees of dispersion and these can travel up to millions of parsecs. One parsec is about 3.26 light years, so the nearest star to us, Proxima Centauri, is about 1.3 parsecs (4.2 light years) from the sun. The jets can leave a galaxy, and there are images from Hubble where the length of the jet dwarfs the galaxy from which it came. On the other hand, the black hole at the centre of our galaxy does not currently generate such a jet. In the Chandra X-ray image you can see the jet coming out of the M 87 system. (There will be another on exactly the other side of the system.)

This is one of the most powerful events that occur in the Universe, and while we have a qualitative idea of some of what might be powering it, the details are still to be worked out. One theory is that as the plasma spirals into the black hole, the magnetic field gets compressed and rotates, and this magnetic field then exerts a force on the plasma, with the net result that matter is ejected in a jet from the inner regions around the black hole. There is at least one alternative theory. Roger Penrose has proposed that the rotating black hole causes “frame dragging”, which can extract relativistic energies and momentum, essentially from the spin of the black hole. Of course the material being ejected did not come from the black hole, but rather some of the material falling into the black hole is caught before it reaches it and from whatever the cause is ejected at these fantastic energies. The net result is that energy and angular momentum are removed, which also aids the black hole to accrete more mass.

Which raises the question, why does the black hole at the centre of our galaxy not do this? The simple answer may well be that there is no matter close enough to fall in, and what is nearby is in stars that are stable and in a stable orbit. There is a lot we do not know about black holes, and we are unlikely to in the near future.

The M 87 Black Hole

By now, unless you have been living under a flat rock somewhere, you have probably seen an image of a black hole. This image seems to be in just about as many media outlets as possible, so you know what the black hole and its environs look like, right? Not necessarily. But, you say, you have seen a photograph. Well, actually, no you haven’t. That system is so far away that to get the necessary resolution you need to gather light over a very wide array, so the image was obtained from a very large number of radio telescopes and the image was reconstructed by a sequence of mathematical processes. Nevertheless, the black sphere and the ring will represent fairly accurately part of what is there.

No radiation can escape from a black hole so the black bit in the middle is fair, however the image as presented gives no idea of its size. Its radius is about 19 billion km, which is a little under five times the distance from the sun to Pluto. This is really a monster. Ever wondered what happens to photons that are emitted at right angles to the gravitational field? Well, at 28 billion km or thereabouts they go into orbit around the black hole and would do that for an infinite time unless they get absorbed by dust falling in. The bright stuff you see is outside the rotating photons, and is travelling clockwise at about half light speed.

The light is obviously not orange and the signals were received as radio waves, but when emitted they would be extremely high energy photons. We see them as radio waves because they have lost that much energy climbing out of the black hole’s gravitational field. One way of looking at this is to think of light as a wave. The more energy the light has, the greater the frequency of wave crests passing by. As the energy lowers due to gravity lowering the energy of the light, the wave gets “stretched” and the number of crests passing by lowers. At the edge of the black hole the wave is so stretched it takes an infinite amount of time for a second crest to appear, which means no light can escape. Just outside the event horizon the gravity is not quite strong enough to stop it, but a gamma ray wave might take 100,000 of our years for the next crest to pass when it gets to us. The wave is moving but it is so red-shifted we could not see it. Further away from the event horizon the light is a little less stretched, so we see it as radio waves, which is what we were looking at in this image, even if it still started as gamma rays or Xrays.

It has amused me to see the hagiolatry bestowed upon Einstein regarding this image. One quote: “Albert Einstein’s towering genius is on display yet again.” As a comment, I am NOT trying to run down Einstein, but let us be consistent here. You may note Newton also predicted a mass at which light could not escape. In Newtonian mechanics the energy of the light would be given by E =mc^2/2, while the gravitational potential energy would be GMm/R. This permits us to calculate a radius where light cannot escape as R = 2GM/c^2, which happens to be exactly the same as the Schwarzchild radius from General Relativity.

Then we see statements such as “General relativity describes gravity as a consequence of the warping of space-time.” Yes, but that implies something that should not be there. General Relativity is a geometric theory, and describes the dynamics of particles in geometric terms. The phrase “as a consequence of” should be replaced with “in terms of”. The use of “consequence” implies cause, and this leads to statements involving cosmic fabric being bent, and you get images of something like a trampoline sheet, which is at best misleading. Here is another quote that annoys me: “Massive objects create a sort of dent or well in the cosmic fabric, which passing bodies fall into because they’re following curved contours (not as a result of some mysterious force at a distance, which had been the prevailing view before Einstein came along)”. No! Both theories are done a great disservice. Einstein gave a geometric description of how bodies move, but there is no physical cause, and it has the same problem, only deeper, than the Newtonian description had, because you must then ask, how does one piece of space-time know exactly how much to distort? Meanwhile, Newton gave a description of the dynamics of particles essentially in terms of calculus. Whereas Einstein describes effects in terms of a number of tensors, which most people do not understand, Newton invented the term “force”.

Now you will often see the argument that light is bent around the sun and that “proves” General Relativity is correct. Actually, Newtonian physics predicted  the same effect, but general Relativity bends it twice as much as predicted by Newtonian physics, so yes, in that sense General relativity is correct if the bend is correctly found to be twice that of Newton. You will then see statements along the lines this proves the bent path is “due to the warping of spacetime”. That is, of course, nonsense. The reason is that in Einstein’s relativity E = mc^2, which is twice that of the Newtonian energy, as you can see from the above. The reason for the difference appears to be the cosmic speed limit of light speed, which Newton may or may not have considered, but had no reason to go further. Why do I say Newton might have considered it? Because as a postulate, the fundamental nature of the speed of light goes all the way back to Empedocles. Of course, he did not make much of it.

Finally, I saw one statement that “the circular nature of the black hole again confirms the correctness of Einstein’s theory of General Relativity. Actually, Aristotle provided one of the first recorded reasons why gravity leads to a sphere. Newton would certainly have predicted a basic sphere, and of course the algorithm used to make the image would not have led to any other result unless there were something really dramatically non spherical. The above is not intended to downplay Einstein, but I am not a fan of the hagiolatry that accompanies him either.

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.