Support for a Predicted Mechanism!

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

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

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

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


Planets for alien life (3)

We have a suitable star, but will it have planets? Let me confess at once – I would generally be regarded as being a heretic on this subject, so be warned. The standard theory argues that they form through the gravitational attraction of planetesimals during the second stage of stellar accretion, but it has no mechanism by which planetesimals form, so there isn’t much more to be said about that. In my view, the planets formed in a completely different way, which involves the chemistry that should take place in the accretion disk and the material gradually heats up as it approaches the star.

In my proposal (more details in my ebook, Planetary formation and biogenesis) the four outer planets form the same way snow-balls form: the pressure induced merging of particles that melt-welds the ices into a larger body when collisions occur a little below the melting point of the ice. There are four major ices, with increasing melting points: nitrogen/carbon monoxide; methane/argon; ammonia/methanol/water; water. Bodies will contain the ices that have yet to melt, so all have water as the major component, and the water should hold the more volatile ices in pores. We then have four giants, in order Neptune, Uranus, Saturn and Jupiter. The satellites form the same way, and the internal chemistry of Saturn converts methanol and ammonia into some methane and nitrogen, which is why Titan (a Saturnian satellite) has an atmosphere, and the somewhat larger Jovian satellites do not. In the ebook I show that the planets are at positions that roughly correspond to the expected temperature profile in the disk when they are formed.

You may be skeptical at this point – where are such exoplanets? The reason why hardly any have been found is that they are difficult to find. Remember how long it took to find Neptune? However, one such system has been found: HR 8799. These planets are at 68 A.U. (1 A.U. is the earth-sun distance), 38 A.U, 24 A.U. and 14.5 A.U. and these distances are proportionately similar to those in our solar system, only more spaced out. The greater distances will arise from more energy being converted to heat, through a larger star (more gravitational energy produced per unit mass) or faster accretion (more mass per unit time). So, why is there only one such system discovered? One reason why these planets were detected is that the inner three are about 9 times bigger than Jupiter, and they have only just formed. Their temperature is about 1100 degrees, so they shine, and we can see them! This is rather exceptional. The two main means of finding planets are the Doppler effect, where the planet pulls on the star as it orbits, and its motion has a “wobble” that can be detected, or, with the Kepler telescope, the planet passes in front of the star, giving a transit effect. Both of these favour finding planets close to the star. The Doppler effect is bigger the larger and closer the planet because that gives it a bigger pull, while to observe a transit, the planet has to be on a line between the observer and the star. Close up, there is more angular tolerance because the star is so big, and there may be, say, 2-3 degrees tolerance. If the planet is as far away as Neptune, there is essentially no tolerance, and there is a further problem: a transit cannot happen more often than once the planet’s “year”. For Neptune, that is about once in 165 years. Kepler has been going only a few years and will soon stop.

The giants are hardly likely to have life as we know it, however giants are important because if the giants grow too big and are too close together, their gravitational interactions start to disrupt their orbits, which at first should become more elliptical, and then start moving each other around. The larger the giants, and the closer they are together, the more disruptive they are. Given sufficient time, they may throw one or more of the giants out of the system, while the Jupiter equivalent moves closer to the star, often becoming a star-grazing planet. If it did that, it would most likely totally disrupt rocky planets. So, the number of suitable stars must be reduced by the probability that the giants stay where they are. Since we cannot, in general, see giants in their proposed original positions, it is hard to estimate that probability, but as noted in the last post, the factor will be something less than a half.

There is still one further problem. If, around the Jupiter position, more than one planet started to grow, subsequent gravitational; interactions could lead to one of the bodies being flung inwards, where, if it is big enough, it may continue to grow. This could produce anything from a water world to a small giant. It is rather difficult to guess the probability of that happening. However, if I am correct, all of those with giants in the right position and which only formed one significant Jupiter-type precursor will be likely to have rocky planets in the habitable zone, and of course, a water world does not prohibit life (although there will be no technology – it is hard to invent fire under water!) There are still plenty of stars!