No Phosphine on Venus

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

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

Planets Being Formed Now

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

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

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

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

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

Betelguese Fades

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

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

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

A Spanner in the Cosmological Works

One of the basic assumptions in Einstein’s relativity is that the laws of physics are constant throughout the Universe. One of those laws is gravity, and an odd thing about gravity is that matter always attracts other matter, so why doesn’t everything simply collapse and fall to one gigantic mass? Einstein “explained” that with a “cosmological constant” which was really an ad hoc term put there to stop that happening. Then in 1927 Georges Lemaȋtre, a Belgian priest proposed that the Universe started off as a tiny incredibly condensed state that expanded, and is still expanding –  the so-called “Big Bang”. Hubble then found that on a sufficiently large scale, everything is moving away from the rest, and it was possible to extrapolate back in time to see when it all started. This was not universally agreed until the cosmic microwave background, which is required by this theory, was detected, and detected more or less in the required form. All was well, until eventually, three “problems” were perceived to arise: the “Horizon problem”, the “Flatness problem”, and the “Magnetic monopole problem”.

The Horizon problem is that on a sufficiently large scale, everything looks the same. The problem is, things are moving away from each other at such great distances, so how did they come into thermal equilibrium when there was no contact between them? I must confess I do not understand this. If the initial mass is a ball of uniform but incredibly dense energy, then if it is uniform, and if the expansion is uniform, everything that happens follows common rate equations, so to get the large-scale uniformity, all you need is the uniform expansion of the energy and a common clock. If particle A wants to decay, surely it does not have to get permission from the other side of the Universe. The flatness problem is that the Universe seems to behave as if it followed Euclidean geometry. In the cosmological models, this requires a certain specific particle density. The problem is, out of all the densities, why is it more or less exactly right? Is this reasoning circular, bearing in mind the models were constructed to give what we see? The cosmic microwave background is a strong indication that Euclidean geometry is correct, but maybe there are other models that might give this result with less difficulties. Finally, the magnetic monopole problem is we cannot find magnetic monopoles. In this context, so far all electromagnetism is in accord with Maxwell’s electromagnetic theory and its equations exclude magnetic monopoles. Maybe we can’t find them because the enthusiasts who argue they should be there are wrong.

Anyway, around 1980, Alan Guth introduced a theory called inflation that would “solve” these problems. In this, within 10^-36 seconds after the big bang (that is 1 second of time divided by10 multiplied by itself 36 times) the Universe made a crazy expansion from almost no volume to something approaching what we see now by 10^-32 seconds after the big bang, then everything slowed down and we get what we have now – a tolerably slowly expanding Universe but with quantum fluctuations that led to the galaxies, etc that we see today. This theory “does away” with these problems. Mind you, not everyone agrees. The mathematician Roger Penrose has pointed out that this inflation requires extremely specific initial conditions, so not only has this moved the problem, but it made it worse. Further, getting a flat universe with these mathematics is extremely improbable. Oops.

So, to the spanner. Scientists from UNSW Sydney reported that measurements on light from a quasar 13 billion light years away found that the fine structure constant was, er, not exactly constant. The fine structure constant α is

α=e2/2εoch

The terms are e the elementary electric charge, εo is the permittivity of free space, c is the sped of light, and h is Planck’s constant, or the quantum of action. If you don’t understand the details, don’t worry. The key point is α is a number (a shade over 137) and is a ratio of the most important constants in electromagnetic theory. If that is not constant, it means all of fundamental physics is not constant.  No only that, but in one direction, the strength of the electric force appeared to increase, but in the opposite direction, decrease. Not only that but a team in the US made observations about Xrays from distant galaxies, and found directionality as well, and even more interesting, their directional axis was essentially the same as the Australian findings. That appears to mean the Universe is dipolar, which means the basic assumption underpinning relativity is not exactly correct, while all those mathematical gymnastics to explain some difficult “problems” such as the horizon problem are irrelevant because they have concluded how something occurred that actually didn’t. Given that enthusiasts do not give up easily I expect soon there will be a deluge of papers explaining why it had tp be dipolar.

Puffy Planets

It is possible now with exoplanets to determine their mass, e.g. by measuring a wobble in the star’s motion due to the pull of the planet, and if the planet transits the star, you can measure its size because the light you see from the star starts to dim when the planet starts to transit, and the last of the dimming is when the other side emerges. You get a secondary measurement when it stops dimming at the bottom of the light graph, and starts brightening. You know the speed at which it crosses because you have measured its “year”, or orbital period. If you know its size and you know its mass, you can work out its density, which gives clues as to what it is made of.

Consider the following densities in g/cm cubed:  Earth 5.51, Mercury 5.43, Venus 5.24, Mars, 3.93, Neptune, 1.64, Uranus, 1.27, Jupiter, 1.33, Saturn, 0.69. What we get from that is that since rocks have densities between 2.5 – 3 for felsic rocks, and 3 – 4 for basalt, and iron has a density of about 7.8, Earth, Mercury and Venus all have significant iron cores, Mars will have only a small one at best, and the other planets have a lot of gas. However, they have to have cores. The usual theory of planetary formation is that the planet starts with a core, it grows, and when it gets big enough it starts to attract gas. The cores in the outer solar system will comprise ices and silicates, while in the rocky planet zone, because the accretion disk is hotter, the ice has vaporized so we are restricted to rocks. If a rocky planet gets big enough that its gravity can hold gas, it too can become a giant. That is the theory, anyway. Our assessment of Neptune is that while the core is icy, it will also have silicates, and it took it until about 10 earth masses before it started accreting gas rapidly. Uranus would be similar, but the reason it is less dense is, at least in my interpretation, because as the disk gets denser the closer to the star, once it started accreting gas it could do so faster than Neptune could. Accordingly, since they are the same size, Neptune had to grow more core, and in my opinion, that was due to the mechanism of core formation. However, that is not relevant here. As you can see, the lowest density is Saturn, because it is full of hydrogen and helium. Jupiter is denser because, in my opinion, it accreted gas faster and the heat boiled off a lot of hydrogen and helium, which is why it has about three times the amount of gases such as nitrogen compared with hydrogen as the sun, and, of course, the stronger gravity compresses gas better. (The sun was also much hotter, but it has far more gravity.)

There is another theory of planetary formation, where the gas disk becomes unstable and collapses. This may well occur, but it usually is considered to work a long way from the star. One reason is, unless the two instabilities occur at the same time, when you get a double star, if the planetary material is orbiting the star, the closer it is to the star the orbital speeds are different at different distances and the instability would shear. Planets have to be reasonably close to the star to get a transit recorded frequently enough.

Anyway, puffy planets. If we look at Kepler 87 c, it is a planet close to a star the size of the sun and towards the end of its life in the main sequence. It is about as far away as Venus and about 6.4 times Earth’s mass, so it is not expected to be able to hold big atmospheres, yet its density is 0.152 g/cm cubed. The planet HIP 41378 f is an even worse problem. It has a mass very similar to Uranus, the star is 1.15 the size of the sun, and the planet is about 1.37 times further from the star than Earth is from the sun. Interestingly, if it had a big enough satellite, that’s satellite would be in the habitable zone.  However, the planet is definitely weird: its density is approximately 0.09 g/cm cubed. That qualifies as a super-puff. There are a number of planets with densities less than 0.3 g/cm cubed, so for whatever reason, they are not freaks.

The question now is, how could a planet have such a low density? I suppose observational error cannot be entirely ruled out, but I think it should be. If there were just one, maybe we could be skeptical, but that many? The next possibility might be they are still accreting, but Kepler 87 c cannot be accommodated by that explanation because the star is so old. Further, if a giant is accreting gas, it gets very hot (we have seen these in newly forming planets) and these super-puffs are cold. Another guess might be that for some reason the atmosphere is extended far beyond what is expected. There are two reasons why this won’t be right. The first is gravity. If the planet is a giant, its gravity is strong enough to suck the gas in close. If there were more gas the planet would grab it. The second is light would get through and we would expect a spectral change during the eclipse, but we don’t see that.

So, what is the explanation? A recent proposal, and one that I think looks good, is that what we are seeing is a planet with rings, like Saturn. The rings have to be dense enough to block off quite a bit of the light passing through them, but what we are seeing is something similar to what Galileo thought Saturn was. If HIP 42378 f  had rings going out to 2.6 times the planetary radius, its density would be 1.23 g/cm cubed, very similar to Uranus. Now, if we go back to the habitable moon, maybe that is not so silly after all. Why do rings form? One possibility is that some gigantic collision caused a lot of fragments, and some of them came in within the Roche limit, and fragmented. The Saturnian system is consistent with this – a lot of small moons, including some at Lagrange points of larger ones, and one anomalously very large moon. And as an aside, an alien using these sort of measurements would conclude Saturn was an exceptional super-puff. 

Can you Think like a Scientist?

Ever wondered how science works? Feel you know? If so, read this slowly. There is a puzzle to solve so don’t cheat and read past the question before trying to answer. 

WASP 76b is a planet circulating the star known as WASP 76. (WASP stands for “wide angle search for planets” and is an international consortium searching for exoplanets by using robotic telescopes in both hemispheres, hence wide angle. It searches by looking for transits, i.e. a planet passing in front of the star and dimming it. The 76 presumably means the 76th star of interest, and the b means the first planet to be discovered around that particular star.) The star is an F7 class, with a mass of about 1.46 that of the sun, and an effective temperature of about 6,000 oC. So it is bigger, brighter and hotter than the sun.

This planet is weird, by any standards. It is about 0.92 times the size of Jupiter, which means it is a gas giant, and it is 0.033 AU from the centre of the star. (The Earth-Sun distance is defined as 1 AU.) That is close, especially since the star is bigger than the sun. The time taken to go around the star is 1.809886 days. That means a birthday every second day our time, not that there will be anyone having birthdays. The news media has got hold of this because being so close it is expected that the planet is tidally locked. That means, like the Moon going around the Earth, one side is always facing the star and the other side is always facing away. This means that if that is correct and it is tidally locked, the side facing the star will have a temperature of about 2,400 oC, but the side facing away would have a temperature about 1,000 degrees cooler.

When a planet transits in front of the star, the material in the atmosphere absorbs starlight, which gives slightly darker spectral lines, and these give clues as to what is in the atmosphere. In this case, lines corresponding to iron were seen in the gas. At first sight, that is not surprising at 2,400 C. The melting point of iron is 1538 oC, while the boiling point, at our atmospheric pressure, is 2862 oC.  It is not hot enough to boil iron, but then again Earth has temperatures that are nowhere near hot enough to boil water, but plenty of water gets into the atmosphere as clouds, and comes down as rain.

This is where the media have sat up and taken notice: it appears it might be raining iron on that planet. That is weird. More evidence was cited for the rain in that the iron signal was unevenly distributed. Recall the light has to go through the atmosphere, so what we see is the signal from the edges. That signal is not evenly distributed, and apparently present on the evening side, but not in the transition edge from night to day. This was interpreted as due to the iron condensing out as it entered the cold side, and there would be liquid iron droplets as rain during the night. Now, here is your test as a potential scientist. Stop reading and think, and answer this question: do you see anything inconsistent in the above description? This is a test for potential theorists. Theories are not developed by brilliant insights, but rather by thinking that something we think is right has an inconsistency.

Anyway, what struck me is the planet allegedly has a morning and an evening. It cannot have that if it is tidally locked, because the same parts always face the star the same way. The planet must be rotating. As an aside, it is hard to see how it could be tidally locked because the gas in the atmosphere will be travelling extremely fast – the winds and storms will be ferocious if there is a thousand degree difference between night and day. But if it is rotating, maybe the difference is not that much. We cannot measure the dayside from transits. Also, if it were tidally locked, we might expect the iron to rain out on the dark side, but then what? How would it get back to the dayside? After a while it would all be on the night side. There has to be some rotation somewhere.Another interesting point is how do you tidally lock gas? And what does rotation of a gas giant mean? In the case of Jupiter we know it rotates because characteristic storms mark the rotation, but Jupiter is far enough from the star that the temperature differences between night and day are trivial. The hot gas around WASP 76b must move. If it is always going the same way, is the planet rotating or merely the gas has a uniform wind?

Galactic Collisions

As some may know, the Milky Way galaxy and the Andromeda galaxy are closing together and will “collide” in something like 4 – 5 billion years. If you are a good distance away, say in a Magellenic Cloud, this would look really spectacular, but what about if you were on a planet like Earth, right in the middle of it, so to speak? Probably not a lot of difference from what we see. There could be a lot more stars in the sky (and there should be if you use a good telescope) and there may be enhanced light from a dust cloud, but basically, a galaxy is a lot of empty space. As an example, light takes 8 minutes and twenty seconds to get from the sun to Earth. Light from the nearest star takes 4.23 years to get here. Stars are well-spaced.

As we understand it, stars orbit the galactic centre. The orbital velocity of our sun is about 828,000 km/hr, a velocity that makes our rockets look like snails, but it takes something like 230,000,000 years to make an orbit, and we are only about half-way out. As I said, galaxies are rather large. So when the galaxies merge, there will be stars going in a lot of different directions until things settle down. There is a NASA simulation in which, over billions of years, the two pass through each other, throwing “stuff” out into interstellar space, then they turn around and repeat the process, except this time the centres merge, and a lot more “stuff” is thrown out into space. The meaning of “stuff” here is clusters of stars. Hundreds of millions of stars get thrown out into space, many of which turn around and come back, eventually to join the new galaxy. 

Because of the distance between stars the chances of stars colliding comes pretty close to zero, however, it is possible that a star might pass by close enough to perturb planetary orbits. It would have to come quite close to affect Earth, as, for example, if it came as close as Saturn, it would only make a minor perturbation to Earth’s orbit. On the other hand, if that close it could easily rain down a storm of comets, etc, from further out, and seriously disrupt the Kuiper Belt, which could lead to extinction-type collisions. As for the giant planets, it would depend on where they were in their orbit. If a star came that close, it could be travelling at such a speed that if Saturn were on the other side of the star it could know little of the passage.

One interesting point is that such a galactic merger has already happened for the Milky Way. In the Milky Way, the sun and the majority of stars are all in orderly near-circular orbits around the centre, but in the outer zones of the galaxy there is what is called a halo, in which many of the stellar orbits are orbiting in the opposite direction. A study was made of the stars in the halo directly out from the sun, where it was found that there are a number of the stars that have strong similarities in composition, suggesting they formed in the same environment, and this was not expected. (Apparently how active star formation is alters their composition slightly. These stars are roughly similar to those in the Large Magellenic Cloud.)  This suggests they formed from different gas clouds, and the ages of these different stars run from 13 to 10 billion years ago. Further, it turned out that the majority of the stars in this part of the halo appeared to have come from a single source, and it was proposed that this part of the halo of our galaxy largely comprises stars from a smaller galaxy, about the size of the Large Magellenic Cloud that collided with the Milky Way about ten billion years ago. There were no comments on other parts of the halo, presumably because parts on the other side of the galactic centre are difficult to see.

It is likely, in my opinion, that such stars are not restricted to the halo. One example might be Kapteyn’s star. This is a red dwarf about eleven light years away and receding. It, too, is going “the wrong way”, and is about eleven billion years old. It is reputed to have two planets in the so-called habitable zone (reputed because they have not been confirmed) and is of interest in that since the star is going the wrong way, presumably as a consequence of a galactic merger, this shows the probability running into another system sufficiently closely to disrupt the planetary system is of reasonably low probability.

A Planet Destroyer

Probably everyone now knows that there are planets around other stars, and planet formation may very well be normal around developing stars. This, at least, takes such alien planets out of science fiction and into reality. In the standard theory of planetary formation, the assumption is that dust from the accretion disk somehow turns into planetesimals, which are objects of about asteroid size and then mutual gravity brings these together to form planets. A small industry has sprung up in the scientific community to do computerised simulations of this sort of thing, with the output of a very large number of scientific papers, which results in a number of grants to keep the industry going, lots of conferences to attend, and a strong “academic reputation”. The mere fact that nobody knows how to get to their initial position appears to be irrelevant and this is one of the things I believe is wrong with modern science. Because those who award prizes, grants, promotions, etc have no idea whether the work is right or wrong, they look for productivity. Lots of garbage usually easily defeats something novel that the establishment does not easily understand, or is prepared to give the time to try.

Initially, these simulations predicted solar systems similar to ours in that there were planets in circular orbits around their stars, although most simulations actually showed a different number of planets, usually more in the rocky planet zone. The outer zone has been strangely ignored, in part because simulations indicate that because of the greater separation of planetesimals, everything is extremely slow. The Grand Tack simulations indicate that planets cannot form further than about 10 A.U. from the star. That is actually demonstrably wrong, because giants larger than Jupiter and very much further out are observed. What some simulations have argued for is that there is planetary formation activity limited to around the ice point, where the disk was cold enough for water to form ice, and this led to Jupiter and Saturn. The idea behind the NICE model, or Grand Tack model (which is very close to being the same thing) is that Uranus and Neptune formed in this zone and moved out by throwing planetesimals inwards through gravity. However, all the models ended up with planets being in near circular motion around the star because whatever happened was more or less happening equally at all angles to some fixed background. The gas was spiralling into the star so there were models where the planets moved slightly inwards, and sometimes outwards, but with one exception there was never a directional preference. That one exception was when a star came by too close – a rather uncommon occurrence. 

Then, we started to see exoplanets, and there were three immediate problems. The first was the presence of “star-burners”; planets incredibly close to their star; so close they could not have formed there. Further, many of them were giants, and bigger than Jupiter. Models soon came out to accommodate this through density waves in the gas. On a personal level, I always found these difficult to swallow because the very earliest such models calculated the effects as minor and there were two such waves that tended to cancel out each other’s effects. That calculation was made to show why Jupiter did not move, which, for me, raises the problem, if it did not, why did others?

The next major problem was that giants started to appear in the middle of where you might expect the rocky planets to be. The obvious answer to that was, they moved in and stopped, but that begs the question, why did they stop? If we go back to the Grand Tack model, Jupiter was argued to migrate in towards Mars, and while doing so, throw a whole lot of planetesimals out, then Saturn did much the same, then for some reason Saturn turned around and began throwing planetesimals inwards, which Jupiter continued the act and moved out. One answer to our question might be that Jupiter ran out of planetesimals to throw out and stopped, although it is hard to see why. The reason Saturn began throwing planetesimals in was that Uranus and Neptune started life just beyond Saturn and moved out to where they are now by throwing planetesimals in, which fed Saturn’s and Jupiter’s outwards movement. Note that this does depend on a particular starting point, and it is not clear to me  that since planetesimals are supposed to collide and form planets, if there was an equivalent to the masses of Jupiter and Saturn, why did they not form a planet?

The final major problem was that we discovered that the great bulk of exoplanets, apart from those very close to the star, had quite significant elliptical orbits. If you draw a line through the major axis, on one side of the star the planet moves faster and closer to it than the other side. There is a directional preference. How did that come about? The answer appears to be simple. The circular orbit arises from a large number of small interactions that have no particular directional preference. Thus the planet might form from collecting a huge number of planetesimals, or a large amount of gas, and these occur more or less continuously as the planet orbits the star. The elliptical orbit occurs if there is on very big impact or interaction. What is believed to happen is when planets grow, if they get big enough their gravity alters their orbits and if they come quite close to another planet, they exchange energy and one goes outwards, usually leaving the system altogether, and the other moves towards the star, or even into the star. If it comes close enough to the star, the star’s tidal forces circularise the orbit and the planet remains close to the star, and if it is moving prograde, like our moon the tidal forces will push the planet out. Equally, if the orbit is highly elliptical, the planet might “flip”, and become circularised with a retrograde orbit. If so, eventually it is doomed because the tidal forces cause it to fall into the star.

All of which may seem somewhat speculative, but the more interesting point is we have now found evidence this happens, namely evidence that the star M67 Y2235 has ingested a “superearth”. The technique goes by the name “differential stellar spectroscopy”, and what happens is that provided you can realistically estimate what the composition should be, which can be done with reasonable confidence if stars have been formed in a cluster and can reasonably be assigned as having started from the same gas. M67 is a cluster with over 1200 known members and it is close enough that reasonable details can be obtained. Further, the stars have a metallicity (the amount of heavy elements) similar to the sun. A careful study has shown that when the stars are separated into subgroups, they all behave according to expectations, except for Y2235, which has far too high a metallicity. This enhancement corresponds to an amount of rocky planet 5.2 times the mass of the earth in the outer convective envelope. If a star swallows a planet, the impact will usually be tangential because the ingestion is a consequence of an elliptical orbit decaying through tidal interactions with the star such that the planet grazes the external region of the star a few times before its orbital energy is reduced enough for ingestion. If so, the planet should dissolve in the stellar medium and increase the metallicity of the outer envelope of the star. So, to the extent that these observations are correctly interpreted, we have the evidence that stars do ingest planets, at least sometimes.

For those who wish to go deeper, being biased I recommend my ebook “Planetary Formation and Biogenesis.” Besides showing what I think happened, it analyses over 600 scientific papers, most of which are about different aspects.

Space News

There were two pieces of news relating to space recently. Thirty years ago we knew there were stars. Now we know there are exoplanets and over 4,000 of them have been found. Many of these are much larger than Jupiter, but that may be because the bigger they are, the easier it is to find them. There are a number of planets very close to small stars for the same reason. Around one giant planet there are claims for an exomoon, that is a satellite of a giant planet, and since the moon is about the size of Neptune, i.e.the Moon is a small giant in its own right, it too might have its satellite: an exomoonmoon. However, one piece of news is going to the other extreme: we are to be visited by an exocomet. Comet Borisov will pass by within 2 A.U. of Earth in December. It is travelling well over the escape velocity of the sun, so if you miss it in December, you miss it. This is of some interest to me because in my ebook “Planetary Formation and Biogenesis” I outlined the major means I believe were involved in the formation of our solar system, but also listed some that did not leave clear evidence in our system. One was exo-seeding, where something come in from space. As this comet will be the second “visitor” we have recorded recently, perhaps they are more common than I suspected.

What will we see? So far it is not clear because it is still too far away but it appears to be developing a coma. 2 A.U. is still not particularly close (twice the distance from the sun), so it may be difficult to see anyway, at least without a telescope. Since it is its first visit, we have no real idea how active it will be. It may be that comets become better for viewing after they have had a couple of closer encounters because from our space probes to comets in recent times it appears that most of the gas and dust that forms the tail comes from below the surface, through the equivalent of fumaroles. This comet may not have had time to form these. On the other hand, there may be a lot of relatively active material quite loosely bound to the surface. We shall have to wait and see.

The second piece of news was the discovery of water vapour in the atmosphere of K2-18b, a super-Earth that is orbiting an M3 class red dwarf that is a little under half the size of our sun. The planet is about eight times the mass of earth, and has about 2.7 times the radius. There is much speculation about whether this could mean life. If it has, with the additional gravity, it is unlikely that, if it did develop technology, it would be that interested in space exploration. So far, we know there is probably another planet in the system, but that is a star-burner. K2-18b orbits its star in 33 days, so birthdays would come round frequently, and it would receive about five per cent more solar radiation than Earth does, although coming from a red dwarf, there will be a higher fraction of infra-red light and less visible.

The determination of the water could be made because first, the star is reasonably bright so good signals can be received, second, the planet transits across the star, and third, the planet is not shrouded with clouds. What has to happen is that as the planet transits, electromagnetic radiation from the star is absorbed by any molecule at the frequency determined by the bond stretching or bending energies. The size of the planet compared with its mass is suggestive of a large atmosphere, i.e.it has probably retained some of the hydrogen and helium of the accretion disk. This conclusion does have risks because if it were primarily a water or ice world (water under sufficient pressure forms ice stable at quite high temperatures) then it would be expected to have an even greater size for the mass.

The signal was not strong, in part, from what I can make out, it was recorded in the overtone region of the water stretching frequency, which is of low intensity. Accordingly, it was not possible to look for other gases, but the hope is, when the James Webb telescope becomes available and we can look for signals in the primary thermal infrared spectrum, this planet will be a good candidate.So, what does this mean for the possibilities of life? At this stage, it is too early to tell. The mechanism for forming life as outlined in my ebook, “Planetary Formation and Biogenesis” suggests that the chances of forming life do not depend on planetary size, as long as there is sufficient size to maintain conditions suitable for life, such as an adequate atmospheric pressure, liquid water, and the right components, and it is expected that there will be an upper size, but we do not know what that will be, except again, water must be liquid at temperatures similar to ours. That would eliminate giants. However, more precise limits are more a matter of guess-work. The composition of the planet may be more important. It must be able to support fumaroles and I suspect it should have pre-separated felsic material so that it can rapidly form continents, with silica-rich water emitted, i.e.the type of water that forms silica terraces. That is because the silica acts as a template to make ribose. Ribose is important for biogenesis because something has to link the nucleobases to the phosphate chain. The nucleobases are required because they alone are the materials that form with the chemicals likely to be around, and they alone form multiple hydrogen bonds that can form selectively and add as a template for copying, which is necessary for retaining useful information. Phosphate is important because it alone has three functional sites – two to form a polymer, and one to convey solubility. Only the furanose form of the sugar seems to manage the linkage, at least under conditions likely to have been around at the time and ribose is the only sugar with significant amounts of the furanose form. I believe the absence of ribose means the absence of reproduction, which means the absence of life. But whether these necessary components are there is more difficult to answer.

Gravitational Waves, or Not??

On February 11, 2016 LIGO reported that on September 14, 2015, they had verified the existence of gravitational waves, the “ripples in spacetime” predicted by General Relativity. In 2017, LIGO/Virgo laboratories announced the detection of a gravitational wave signal from merging neutron stars, which was verified by optical telescopes, and which led to the award of the Nobel Prize to three physicists. This was science in action and while I suspect most people had no real idea what this means, the items were big news. The detectors were then shut down for an upgrade to make them more sensitive and when they started up again it was apparently predicted that dozens of events would be observed by 2020, and with automated detection, information could be immediately relayed to optical telescopes. Lots of scientific papers were expected. So, with the program having been running for three months, or essentially half the time of the prediction, what have we found?

Er, despite a number of alerts, nothing has been confirmed by optical telescopes. This has led to some questions as to whether any gravitational waves have actually been detected and led to a group at the Neils Bohr Institute at Copenhagen to review the data so far. The detectors at LIGO correspond to two “arms” at right angles to each other running four kilometers from a central building. Lasers are beamed down each arm and reflected from a mirror and the use of wave interference effects lets the laboratory measure these distances to within (according to the LIGO website) 1/10,000 the width of a proton! Gravitational waves will change these lengths on this scale. So, of course, will local vibrations, so there are two laboratories 3,002 km apart, such that if both detect the same event, it should not be local. The first sign that something might be wrong was that besides the desired signals, a lot of additional vibrations are present, which we shall call noise. That is expected, but what was suspicious was that there seemed to be inexplicable correlations in the noise signals. Two labs that far apart should not have the “same” noise.

Then came a bit of embarrassment: it turned out that the figure published in Physical Review Letters that claimed the detection (and led to Nobel prize awards) was not actually the original data, but rather the figure was prepared for “illustrative purposes”, details added “by eye”.  Another piece of “trickery” claimed by that institute is that the data are analysed by comparison with a large database of theoretically expected signals, called templates. If so, for me there is a problem. If there is a large number of such templates, then the chances of fitting any data to one of them is starting to get uncomfortably large. I recall the comment attributed to the mathematician John von Neumann: “Give me four constants and I shall map your data to an elephant. Give me five and I shall make it wave its trunk.” When they start adjusting their best fitting template to fit the data better, I have real problems.

So apparently those at the Neils Bohr Institute made a statistical analysis of data allegedly seen by the two laboratories, and found no signal was verified by both, except the first. However, even the LIGO researchers were reported to be unhappy about that one. The problem: their signal was too perfect. In this context, when the system was set up, there was a procedure to deliver artificially produced dummy signals, just to check that the procedure following signal detection at both sites was working properly. In principle, this perfect signal could have been the accidental delivery of such an artifical signal, or even the deliberate insertion by someone. Now I am not saying that did happen, but it is uncomfortable that we have only one signal, and it is in “perfect” agreement with theory.

A further problem lies in the fact that the collision of two neutron stars as required by that one discovery and as a source of the gamma ray signals detected along with the gravitational waves is apparently unlikely in an old galaxy where star formation has long since ceased. One group of researchers claim the gamma ray signal is more consistent with the merging of white dwarfs and these should not produce gravitational waves of the right strength.

Suppose by the end of the year, no further gravitational waves are observed. Now what? There are three possibilities: there are no gravitational waves; there are such waves, but the detectors cannot detect them for some reason; there are such waves, but they are much less common than models predict. Apparently there have been attempts to find gravitational waves for the last sixty years, and with every failure it has been argued that they are weaker than predicted. The question then is, when do we stop spending increasingly large amounts of money on seeking something that may not be there? One issue that must be addressed, not only in this matter but in any scientific exercise, is how to get rid of the confirmation bias, that is, when looking for something we shall call A, and a signal is received that more or less fits the target, it is only so easy to say you have found it. In this case, when a very weak signal is received amidst a lot of noise and there is a very large number of templates to fit the data to, it is only too easy to assume that what is actually just unusually reinforced noise is the signal you seek. Modern science seems to have descended into a situation where exceptional evidence is required to persuade anyone that a standard theory might be wrong, but only quite a low standard of evidence to support an existing theory.