What do Organic Compounds Found on Mars Mean?

Last week, NASA announced that organic compounds had been found on Mars. The question then is, what does this mean? First, organic compounds are essentially chemicals formed that involve carbon, which means Mars has carbon besides the carbon dioxide in the atmosphere. The name “organic” comes from the fact that such compounds found by early chemists, with the exception of a very few such as carbon dioxide, came from organisms, hence there is the question, do these materials indicate that Mars had life? The short answer is, the issue remains unresolved. One argument is that if there were no organic compounds on Mars, it obviously did not have life. That it has taken so long to find organic compounds does not say anything about the probability, though, because the surface of Mars is strongly oxidizing, and had any been there, they would have been turned into carbon dioxide. The atmosphere already has a lot of that. The reason none has been found, therefore, is because most of the rovers have not been able to dig very deeply.

I shall try to summarise the results that were reported [Eigenbrode et al., Science 360, 1096–1101 (2018)]. One important point is that the volatiles analysed were obtained by pyrolysing the mudstone the rover dug up, so what was detected may not be the same that was in the rock. The first compounds were identified as aliphatic hydrocarbons, from C1 (methane) to C5, and these were stated to be typical of that obtained from Kerogen or coal on Earth. One problem I had with these data was there were odd-numbered masses, BUT they all indicated that the cause was a fractured hydrocarbon, i.e. the pyrolysis had chopped that bit off something else and produced a radical.

One big problem was they could not say whether nitrogen or oxygen was present ” because mass spectra are not resolvable in EGA and other molecules share the diagnostic m/z values. ” I really don’t understand that. First, the identification of aliphatic hydrocarbons was almost certainly correct, because they form series of signals that are very recognizable to anyone who has done a bit of this work before. They stick out like an organ stop, so to speak. However, the presence of nitrogen species in any reasonable amount should be just as easily identified because while hydrocarbons, and their like with oxygen, basically give even mass signals, nitrogen, because of its valency of 3, gives odd numbered mass signals that is 1 bigger than a hydrocarbon. Now, a few of the fragmentation patterns of hydrocarbons give odd numbered mass signals, but if you cannot tell where the molecular ion is, you do not know what the mass of your molecule is. If all you have are fragmentation ions, then the instrument was somewhat poorly designed to go to Mars. With any experience, you can also tell whether you have oxygenated materials because hydrocarbons go up by adding 14 to the basic ion, and the atomic weight of oxygen is 16. If it has oxygen, it abd the fragments containing oxygen have an entirely different mass.

Of course the authors did note the presence of CO2 and CO. These could arise from the pyrolysis of carboxylic acids and ketones, but that does not mean life. Carboxylic acids would pyrolyse at about 400 – 550 degrees C and ketones a bit higher. They also found aromatic hydrocarbons, thiophenes and some other sulphur containing species. These were explained in terms of sulphur –bearing gases coming in contact, and further chemical reactions then taking place, in other words, these sulphur containing species such as hydrogen sulphide do not necessarily provide any information regarding what formed the original deposit. The sulphurization, however, was claimed to provide a preservative function by protecting against mild oxidation. If it carried out that function, it would be oxidized, and none of the observed materials were.

Unfortunately, the material is not directly associated with anything related to life. The remains of life can give rise to these sort of chemicals, as noted by our crude oil, which is basically hydrocarbon, and formed from life, but then altered by tens of millions of years change. These Martian deposits are believed to be in rocks 3.5 billion years old. However, the materials were also obtained by pyrolysis at temperatures exceeding 500 degrees C. The original molecules could have rearranged, and what we saw was the sort of compounds that organic compounds might rearrange to. Nevertheless, the absence of nitrogen is not encouraging. Nitrogen is present in all protein and nucleic acids, and there tends to be high levels of these in primitive life. Pyrolysis would be expected to produce pyrazines and pyridines, and these should be detectable. Pyrazines, having two nitrogen atoms, tend to give even numbered ions, and give the same mass as a ketone, but since neither was seen, that is irrelevant. Had there been such signals, the fragmentation patterns are quite distinctive if you have done this sort of work before.

Other possible sources of organic compounds, besides carbon, are from chondrites that have landed, and geochemically. It is hard to assess chondrites, because we do not have other information. It is possible to tell the difference between oxygen from chondrites from oxygen from other places (because of the different ratios of isotopes of mass 17 and 18 compared with 16), but they never found oxygen. The materials could be geochemical as well. The same reaction used by Germany to make synthetic petrol during WW2 can occur underground, and make hydrocarbons. So overall, while this is certainly interesting, as is often the case it raises more questions than it answers.

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Tabby’s Star – Affirmation or Misleading?

I hope you all had a good Christmas period. We have been having a heat wave, with temperatures way above normal, and a fairly high humidity as well. Even my cat Horatio can’t get up the energy to pester me for early meals. Anyway, something about astronomy, astrophysics, and even science fiction to start the year. During the break, I entered a debate regarding evidence, which eventually led me to Tabby’s star.

There has been odd behaviour in the star KIC 8462852, sometimes called Boyajian’s star, but more commonly called Tabby’s star, after Tabetha Boyajian, who led the team that discovered the strange behaviour. (Fancy having a star named after you.) The reason it is of interest is it has variable flux, with massive dimmings (up to 22% of total flux that occur with 750 day period) and a number of minor ones (approximately 2% that, because there is a number of them, have not as yet been assigned periods). The star is an F type star, about 1.43 times the size of our sun, and it has a surface temperature of about 6750 oK.

So what is going on? What is causing the light to dim? There are two possibilities: the star itself has a variable output, or something crosses between us and the star, and thus dims it. That, of course, is what happens when a planet crosses in front of the star, and that is what the Kepler telescope looks for. However, a planet crossing does not usually manage such a dimming as this because the planet is compact. For example, during the transit of Venus, you would not notice it on Earth without specially looking for it. To get a 22% reduction in light intensity there has to be something with a very large cross-section getting in the road.

Could the star do it by itself? There are variable stars, but they do not usually behave like this. Some multiple stars do, thus when one star goes behind the other, its light gets cut out, but so far there is no evidence of a companion for Tabby’s star. If the star is variable because it changes output, it usually does so rather slowly, and in ways that an astronomer would recognise. There are exceptions. Extreme magnetic activity or a huge swarm of sunspots might do it but it is difficult to envision this happening with a 750-day period.

Suppose something is getting in the road. For a 750-day period, assuming there is only one major body, it would be about 1.8 AU from its star. (An AU is the distance of Earth from the sun.) That makes it somewhat further from its star than Mars is from ours. One proposal is that if the star is far younger than we think, there may be the remains of an accretion disk, that is, a large mass of dust and small stones that is gravitationally coming together. That raises the objection, why not others at other distances? Also, if the standard theory of planetary formation were correct, this would make the star extremely young, because such an accumulations should create planets. Of course that theory could be wrong, as I believe it is. There have been other proposals such as a swarm of comets, and even the debris from a planetary collision. That is usually strongly rejected, but the logic is interesting. It is asserted the probability of seeing such an event is extremely small. So? Kepler has looked at something like 100,000 stars and found this one event, which makes it rare. Once you have a sample of only one, I do not think a probability argument makes any sense at all since no matter how rare the event, if it happens, it is possible to see it.

Another proposal is a large ringed planet, with Trojans. If that is the case, you will see the large event, and a minor event with about 1/6 the periodicity of the main event before and after it. This at least has the merit of being testable. However, the rings would have to be huge, and in one plane normal to the path of the planet.

One of the more bizarre proposals was that the star is surrounded by parts of a megastructure (a Dyson swarm) constructed by an alien civilization to gather energy from the star. Even in my science fiction, I would not suggest that. It took our planet 4.5 billion years to get a technological society, but we are a very long way from being able to construct such a megastructure, yet others are talking about just possibly this star could still be in its formative years. The other point is, why would any alien want to do that? The proposal was that societies might build them to capture their energy needs, but is that plausible? There are other potential shortages besides energy, including materials that you would have to devote to constructing such a monstrous structure. One problem is the periodicity. If you wanted to capture energy, would you not put it a bit closer to the star? If you put it at half the distance, you only need ¼ the materials to get the same energy.

Then there is the question of the absolute size. To get a 22% dimming, and assuming whatever it is totally eclipses the star, the area has to be a dead minimum of 362 billion square miles. In most cases, it has to be seriously bigger. That is a little under 8,000 times the area of the earth. Given that it would have to have a certain amount of thickness for mechanical strength, the mass of this beast would be a serious fraction of the mass of a rocky planet. Where would aliens get the materials? Destroy a planet?

My guess as to what it is? The mechanism for forming rocky planets outlined in my ebook “Planetary Formation and Biogenesis” was that when the star is accreting, the temperatures in the inner part of the disk get quite high, and where Mercury formed, the rocks and iron got sufficiently hot that the silicates stayed in a sticky molten state long enough for the planet to form. Further out it was hot enough to melt the silicates, but because the distances increase, at that point all that formed were a large number of boulders and lumps of iron encased in rock. As the disk started to run out of material, it would cool down. The boulders would collide and make a lot of dust, some of which acted as a cement. That would permit rocks to come together, and water vapour would set the cement, thus sticking them together. The planet Venus was in a rather delicate position because while the rock density was higher there that at Earth’s position, the temperatures from the star were hotter, and it was more difficult to set the cement. Accordingly, Venus was more difficult to get started. One possibility was that it might not get started, and hence it was predicted that some stars might have a boulder belt around them. These might come together gravitationally, but they would not stick.

Weird though it might seem, Tabby’s star more or less fits what might be expected from that theory. Because of the size of the star, if the initial accretion disk had the same characteristics proportionately to our star, the Earth equivalent would be about 2.75 AU from the star, which puts the “blocking object” more or less where the Venus equivalent should be. If it is as I predicted, there should be effects on the colour of the light, because blue light scatters more than red light if it goes through dust. I am waiting to see what happens. If it does turn out to be a gravitationally focused mass of boulders and dust, remember you heard about it here. Then ask yourself, if the standard theory of planetary formation is actually correct, why has this mass not formed a planet? Then the question is, is this evidence for my theory, or is it something else that is misleading me?

That Was 2017, That Was

With 2017 coming to a close, I can’t resist the urge to look back and see what happened from my point of view. I had plenty of time to contemplate because the first seven months were largely spent getting over various surgery. I had thought the recovery periods would be good for creativity. With nothing else to do, I could write and advance some of my theoretical work, but it did not work but like that. What I found was that painkillers also seemed to kill originality. However, I did manage one e-novel through the year (The Manganese Dilemma), which is about hacking, Russians and espionage. That was obviously initially inspired by the claims of Russian hacking in the Trump election, but I left that alone. It was clearly better to invent my own scenario than to go down that turgid path. Even though that is designed essentially as just a thriller, I did manage to insert a little scientific thinking into the background, and hopefully the interested potential reader will guess that from the “manganese” in the title.

On the space front, I am sort of pleased to report that there was nothing that contradicted my theory of planetary formation found in the literature, but of course that may be because there is a certain plasticity in it. The information on Pluto, apart from the images and the signs of geological action, were well in accord with what I had written, but that is not exactly a triumph because apart from those images, there was surprisingly little new information. Some of which might have previously been considered “probable” was confirmed, and details added, but that was all. The number of planets around TRAPPIST 1 was a little surprising, and there is limited evidence that some of them are indeed rocky. The theory I expounded would not predict that many, however the theory depended on temperatures, and for simplicity and generality, it considered the star as a point. That will work for system like ours, where the gravitational heating is the major source of heat during primary stellar accretion, and radiation for the star is most likely to be scattered by the intervening gas. Thus closer to our star than Mercury, much of the material, and even silicates, had reached temperatures where it formed a gas. That would not happen around a red dwarf because the gravitational heating necessary to do that is very near the surface of the star (because there is so much less falling more slowly into a far smaller gravitational field) so now the heat from the star becomes more relevant. My guess is the outer rocky planets here are made the same way our asteroids were, but with lower orbital velocities and slower infall, there was more time for them to grow, which is why they are bigger. The inner ones may even have formed closer to the star, and then moved out due to tidal interactions.

The more interesting question for me is, do any of these rocky planets in the habitable zone have an atmosphere? If so, what are the gases? I am reasonably certain I am not the only one waiting to get clues on this.

On another personal level, as some might know, I have published an ebook (Guidance Waves) that offers an alternative interpretation of quantum mechanics that, like de Broglie and Bohm, assumes there is a wave, but there are two major differences, one of which is that the wave transmits energy (which is what all other waves do). The wave still reflects probability, because energy density is proportional to mass density, but it is not the cause. The advantage of this is that for the stationary state, such as in molecules, that the wave transmits energy means the bond properties of molecules should be able to be represented as stationary waves, and this greatly simplifies the calculations. The good news is, I have made what I consider good progress on expanding the concept to more complicated molecules than outlined in Guidance Waves and I expect to archive this sometime next year.

Apart from that, my view of the world scene has not got more optimistic. The US seems determined to try to tear itself apart, at least politically. ISIS has had severe defeats, which is good, but the political futures of the mid-east still remains unclear, and there is still plenty of room for that part of the world to fracture itself again. As far as global warming goes, the politicians have set ambitious goals for 2050, but have done nothing significant up to the end of 2017. A thirty-year target is silly, because it leaves the politicians with twenty years to do nothing, and then it would be too late anyway.

So this will be my last post for 2017, and because this is approaching the holiday season in New Zealand, I shall have a small holiday, and resume half-way through January. In the meantime, I wish all my readers a very Merry Christmas, and a prosperous and healthy 2018.

A Ball on Mars

In New Zealand we are approaching what the journalists say is “The Silly Season”, the reason being that what with Christmas and New Year, and with it being in the middle of summer, a lot of journalists take holidays, and the media, with a skeleton staff, have to find almost anything to fill in the spaces that the media makes available. So, in the spirit of getting off to an early start, I noticed an image from Mars that looks as if someone left a cannon ball lying around. (The image is easily found on the web, but details are not, so I am not sure where it was found.) So what is it?

Mars_Ball

Needless to say there were some loopy suggestions from “the fringe”, but while it is easy to scoff, it is not so easy to try to guess what it is. The idea of a cannon ball and nothing else borders on the totally bizarre. So what can we see from the image? The remarkable point about this object is it seems to be lying on the surface, which suggest it did not strike it, as otherwise there would be indentations, or, if it were a meteorite, there would be a crater. There clearly isn’t. Equally, however, it looks smooth, which suggests it has been fused, which means it did not arise there. Some have suggested it is a haematite spherule, but that, to me is not that likely, in part because it is so large (the so-called “blueberries” were quite small) and also because there seems to be only one of it, while what created the “blueberries” created a lot of them. In my opinion, it is probably an iron meteorite, and the reason there is no impact crater is that it landed somewhere else, and rolled to this spot.

So maybe time to get a little more serious, and think about iron meteorites. What can we say about them? The Curiosity rover has also found “Egg rock”, which is an iron meteorite about the size of a golf ball. The Rover found iron, nickel and phosphorus as significant constituents, and the phosphorus is present as iron phosphide. There are two important issues here: how did the iron/nickel ball form separately from everything else, and equally important, how did iron phosphide form? That last question may need explanation, because phosphorus does not normally occur as a phosphide, and phosphides only form under highly reducing conditions. (Reducing conditions are usually in the presence of hydrogen and or an active metal at higher temperatures. The opposite, oxidising conditions, occurs when there is oxygen or water present, but not enough hydrogen or metal to scavenge the oxygen.)

Iron phosphide is known to occur in certain iron meteorites, but such meteorites can always be attributed to having formed at a little more than 1 A.U. from, or closer to the star. Chondrites that formed further out, such as in the asteroid belt, always have their phosphorus in the form of phosphate, which is a very stable, oxidised, phosphorus compound. The point about 1 A.U. (the distance of Earth from the sun) is that was where the temperatures were hot enough to melt iron, and the phosphide would form by the molten iron reacting with phosphate to form the phosphide and iron oxide.

Now for the reason for going on about this. One of the JPL team explained that iron meteorites originated from the cores of asteroids. The premise here is that during initial accretion, the dust assembled into an asteroid-sized object, the object got sufficiently hot and the iron and nickel melted and sunk to the core. Later, there was a massive collision and the asteroid’s core shattered, and the meteorites we see are the fragments from the shattering. (Note, the same people argue planets formed by asteroid sized bodies, and bigger, colliding and everything stick together. Here is having your cake and eating it in action.) The first question is, why did the rock melt? One possibility is radioactive isotopes, so it is possible, nevertheless for the explanation to work the asteroid had to melt hot enough to melt iron, and to hold those temperatures for long enough for the iron to work its way to the centre through the very viscous silicates in a very weak gravitational field. A further problem is that the phosphate would dissolve in the silicates, in which case it would not form iron phosphide because the iron would not get there. Calcium phosphate has a density of about 3, very similar to many of the silicates, so it might be difficult for iron phosphide to form in such an asteroid. Only a very few asteroids, and Vesta is one, have iron cores, and there are some reasons to believe Vesta formed somewhere else and moved.

The reason for my interest is that in my ebook, “Planetary Formation and Biogenesis” I argue that the first way accretion started was for the dust in the accretion disk to get hot enough to get sticky, or to form something that could later act like a cement. When the temperatures got up to about 1550 degrees Centigrade, iron melts and in the disk would form globules that would grow to a certain degree. Many of these would also find molten silicates to coat them, so the separation occurred through the temperature generated by the accreting star. Provided these could separate themselves from the gas flow (and there is at least a plausible mechanism) then these would become the raw materials for rocky planets to form. That is why (at least in my opinion) Earth, Venus and Mercury have large iron cores, but Mars does not.

That, of course, has got a little away from the “Martian cannonball” but part of forming a scientific theory is to let the mind wander, to check that a number of other aspects of the problem are consistent with the propositions. In my view, the presence of iron phosphide in an iron meteorite is most unlikely to have come from the core of an asteroid that got smashed up. I still like my theory, but then again, I suppose I am biased.

Ross 128b a Habitable Planet?

Recently the news has been full of excitement that there may be a habitable planet around the red dwarf Ross 128. What we know about the star is that it has a mass of about 0.168 that of the sun, it has a surface temperature of about 3200 degrees K, it is about 9.4 billion years old (about twice as old as the sun) and consequently it is very short of heavy elements, because there had not been enough supernovae that long ago. The planet is about 1.38 the mass of Earth, and it is about 0.05 times as far from its star as Earth is. It also orbits its star every 9.9 days, so Christmas and birthdays would be a continual problem. Because it is so close to the star it gets almost 40% more irradiation than Earth does, so it is classified as being in the inner part of the so-called habitable zone. However, the “light” is mainly at the red end of the spectrum, and in the infrared. Even more bizarrely, in May this year the radio telescope at Arecibo appeared to pick up a radio signal from the star. Aliens? Er, not so fast. Everybody now seems to believe that the signal came from a geostationary satellite. Apparently here is yet another source of electromagnetic pollution. So could it have life?

The first question is, what sort of a planet is it? A lot of commentators have said that since it is about the size of Earth it will be a rocky planet. I don’t think so. In my ebook “Planetary Formation and Biogenesis” I argued that the composition of a planet depends on the temperature at which the object formed, because various things only stick together in a narrow temperature range, but there are many such zones, each giving planets of different composition. I gave a formula that very roughly argues at what distance from the star a given type of body starts forming, and if that is applied here, the planet would be a Saturn core. However, the formula was very approximate and made a number of assumptions, such as the gas all started at a uniform low temperature, and the loss of temperature as it migrated inwards was the same for every star. That is known to be wrong, but equally, we don’t know what causes the known variations, and once the star is formed, there is no way of knowing what happened so that was something that had to be ignored. What I did was to take the average of observed temperature distributions.

Another problem was that I modelled the centre of the accretion as a point. The size of the star is probably not that important for a G type star like the sun, but it will be very important for a red dwarf where everything happens so close to it. The forming star gives off radiation well before the thermonuclear reactions start through the heat of matter falling into it, and that radiation may move the snow point out. I discounted that largely because at the key time there would be a lot of dust between the planet and the star that would screen out most of the central heat, hence any effect from the star would be small. That is more questionable for a red dwarf. On the other hand, in the recently discovered TRAPPIST system, we have an estimate of the masses of the bodies, and a measurement of their size, and they have to have either a good water/ice content or they are very porous. So the planet could be a Jupiter core.

However, I think it is most unlikely to be a rocky planet because even apart from my mechanism, the rocky planets need silicates and iron to form (and other heavier elements) and Ross 128 is a very heavy metal deficient star, and it formed from a small gas cloud. It is hard to see how there would be enough material to form such a large planet from rocks. However, carbon, oxygen and nitrogen are the easiest elements to form, and are by far the most common elements other than hydrogen and helium. So in my theory, the most likely nature of Ross 128b is a very much larger and warmer version of Titan. It would be a water world because the ice would have melted. However, the planet is probably tidally locked, which means one side would be a large ocean and the other an ice world. What then should happen is that the water should evaporate, form clouds, go around the other side and snow out. That should lead to the planet eventually becoming metastable, and there might be climate crises there as the planet flips around.

So, could there be life? If it were a planet with a Saturn core composition, it should have many of the necessary chemicals from which life could start, although because of the water/ice live would be limited to aquatic life. Also, because of the age of the planet, it may well have been and gone. However, leaving that aside, the question is, could life form there? There is one restriction (Ranjan, Wordsworth and Sasselov, 2017. arXiv:1705.02350v2) and that is if life requires photochemistry to get started, then the intensity of the high energy photons required to get many photochemical processes started can be two to four orders of magnitude less than what occurred on Earth. At that point, it depends on how fast everything that follows happens, and how fast the reactions that degrade them happen. The authors of that paper suggest that the UV intensity is just too low to get life started. Since we do not know exactly how life started yet, that assessment might be premature, nevertheless it is a cautionary point.

Asteroids

If you have been to more than the occasional science fiction movie, you will know that a staple is to have the trusty hero being pursued, but escaping by weaving in and out of an asteroid field. Looks like good cinema, they make it exciting, but it is not very realistic. If asteroids were that common, according to computer simulations their mutual gravity would bring them together to form a planet, and very quickly. In most cases, if you were standing on an asteroid, you would be hard pressed to see another one, other than maybe as a point like the other stars. One of the first things about the asteroid belt is it is mainly empty. If we combined all the mass of the asteroids we would get roughly 4% of the mass of the Moon. Why is that? The standard theory of planetary formation cannot really answer that, so they say there were a lot there, but Jupiter’s gravity drove them out, at the same time overlooking the fact their own theory says they should form a planet through their self-gravity if there were that amny of them. If that were true, why did it leave some? It is not as if Jupiter has disappeared. In my “Planetary formation and Biogenesis”, my answer is that while the major rocky planets formed by “stone” dust being cemented together by one other agent, the asteroid belt, being colder, could only manage dust being cemented together with two other agents, and getting all three components in the same place at the same time was more difficult.

There is a further reason why I do not believe Jupiter removed most of the asteroids. The distribution currently has gaps, called the Kirkwood gaps, where there are very few asteroids, and these occur at orbital resonances with Jupiter. Such a resonance is when the target body would orbit at some specific ratio to Jupiter’s orbital period, so frequently the perturbations are the same because in a given frame of reference, they occur in the same place. Thus the first such gap occurs at 2.06 A.U. from the sun, where any asteroid would go around the sun exactly four times while Jupiter went around once. That is called a 4:1 resonance, and the main gaps occur at 3:1, 5:2, 7:3 and 2:1 resonances. Now the fact that Jupiter can clear out these narrow zones but leave all the rest more or less unchanged strongly suggests to me there were never a huge population of asteroids and we are seeing a small residue.

The next odd thing about asteroids is that while there are not very many of them, they change their characteristics as they get further from the star (with some exceptions to be mentioned soon.) The asteroids closest to the sun are basically made of silicates, that is, they are essentially giant rocks. There appear to be small compositional variations as they get further from the star, then there is a significant difference. How can we tell? Well, we can observe their brightness, and in some cases we can correlate what we see with meteorites, which we can analyse. So, further out, they get significantly duller, and fragments that we call carbonaceous chondrites land on Earth. These contain a small amount of water, and organic compounds that include a variety of amino acids, purines and pyrimidines. This has led some to speculate that our life depended on these landing on Earth in large amounts when Earth was very young. In my ebook “Planetary Formation and Biogenesis”, I disagree. The reasons are that to get enough, a huge number of such asteroids would have to impact the Earth because they are still basically rock, BUT at the same time, hardly any of the silicate based asteroids would have to arrive, because if they did, the isotopes of certain elements on Earth would have to be different. Such isotope evidence also rules these out as a source of water, as does certain ratios such as carbon to chlorine. What these asteroid fragments do show, however, is that amino acids and other similar building blocks of life are reasonably easily formed. If they can form on a lump of rock in a vacuum, why cannot they form on Earth?

The asteroid belt also has the odd weird asteroid. The first is Ceres, the largest. What is weird about it is that it is half water. The rest are essentially dry or only very slightly wet. How did that happen, and more to the point, why did it not happen more frequently? The second is Vesta, the second largest. Vesta is rocky, although it almost certainly had water at some stage because there is evidence of quartz. It has also differentiated, and while the outer parts have olivine, deeper down we get members of the pyroxene class of rocks, and deeper down still there appears to be a nickel/iron core. Now there is evidence that there may be another one or two similar asteroids, but by and large it is totally different from anything else in the asteroid belt. So how did that get there?

I rather suspect that they started somewhere else and were moved there. What would move them is if they formed and came close to a planet, and instead of colliding with it, they were flung into a highly elliptical orbit, and then would circularise themselves where they ended up. Why would they do that? In the case of Vesta, at some stage it suffered a major collision because there is a crater near the south pole that is 25 km deep, and it is from this we know about the layered nature of the asteroid. Such a collision may have resulted in it remaining in orbit roughly near its present position, and the orbit would be circularised due to the gravity of Jupiter. Under this scenario, Vesta would have formed somewhere near Earth to get the iron core. Ceres, on the other hand, probably formed closer to Jupiter.

In my previous post, I wrote that I believed the planets and other bodies grew by Monarchic growth, but that does not mean there were no other bodies growing in a region. Monarchic growth means the major object grows by accreting things at least a hundred times smaller, but of course significant growth can occur for other objects. The most obvious place to grow would be at a Lagrange point of the biggest object and the sun. That is a position where the planet’s gravitational field and the sun’s cancel, and the body is in stable or metastable orbit there. Once it gets to a certain size, however, it is dislodged, and that is what I think was the source of the Moon, its generating body probably starting at L4, the position at the same distance from the sun as Earth, but sixty degrees in front of it. There are other metastable positions, and these may have also formed around Venus or Mercury, and these would also be unstable due to different rocky planets. The reason I think this is that for Vesta to have an iron core, it had to pick up bodies with a lot of iron, and such bodies would form in the hotter part of the disk while the star was accreting. This is also the reason why Earth has an iron core and Mars has a negligible one. However, as I understand it, the isotopes from rocks on Vesta are not equivalent to those of Earth, so it may well have started life nearer to Venus or Mercury. So far we have no samples to analyse that we know came from either of these two planets, and I am not expecting any such samples anytime soon.

A Giant Planet Around a Dwarf Star

The news here, at least, has made much of the discovery of NGTS-1b, described as a giant planet orbiting a dwarf star. It is supposed to be the biggest planet ever found around such a small star, and it is supposed to be inexplicable how such a big planet could form. One key point that presumably everyone will agree with is, a small star forms because there is less gas and dust in the cloud that will form the star than in the cloud that forms a big star. Accordingly there is less total material to form a planet. Missing from that statement is the fact that in all systems the amount of mass in the planets is trivial compared to the mass of the star. Accordingly, there is nothing at all obscure about an unexpectedly big planet if the planet was just a bit more efficient at taking material that would otherwise go into the star.

So, a quick reality check: the star is supposed to be about 60% the size of the sun, and the planet is about 80% the mass of Jupiter, but has a somewhat larger radius. Planets up to twenty times the size of Jupiter are known around stars that are not more than about three times the size of our sun, so perhaps there is more being made of this “big planet” than is reasonable.

Now, why is it inexplicable how such a large planet could form around a small star, at least in standard theory? The mechanism of formation of planets in the standard theory is that first gas pours in, forms the star, and leaves a residual disk (the planetary accretion disk), in which gas is essentially no longer moving towards the star. That is not true; the star continues to accrete, but several orders or magnitude more slowly. The argument then is that this planetary accretion disk has to contain all the material needed to form the planets, and they have to form fast enough to get as big as they end up before the star ejects all dust and gas, which can take somewhere up to 10 million years (10 My), with a mean of about 3 My. There is some evidence that some disks last at least 30 My. Now the dust collides, sticks (although why or how is always left out in the standard theory) and forms planetesimals, which are bodies of asteroid size. These collide and form bigger bodies, and so on. This is called oligarchic growth. The problem is, as the bodies get larger, the distance between them increases and collision probability falls away, not helped by the fact that the smaller the star, the slower the orbiting bodies move, the less turbulent it will be, so the rate of collisions slows dramatically. For perspective purposes, collisions in the asteroid belt are very rare, and when they occur, they usually lead to the bodies getting smaller, not bigger. There are a modest number of such families of detritus asteroids.

The further out the lower the concentration of matter, simply because there is a lot more space. A Jupiter-sized body has to grow fast because it has to get big enough for its gravity to hold hydrogen, and then actually hold it, before the disk gases disappear. Even accreting gas is not as simple as it might sound, because as the gas falls down the planetary gravitational field, it gets hot, and that leads to some gas boiling off back to space. To get going quickly, it needs more material, and hence a Jupiter type body is argued (correctly, in my opinion) to form above the snow line of water ice. (For the purposes of discussion, I shall call material higher up the gravitational potential “above”, in which case “below” is closer to the star.) It is also held that the snow line is not particularly dependent on stellar mass, in which case various planetary systems should scale similarly. With less material around the red dwarf, and as much space to put it in, everything will go a lot slower and the gas will be eliminated before a planet is big enough to handle it. Accordingly, it seems that according to standard theory, this planet should not form, let alone be 0.036 A.U. from the star.

The distance from the star is simply explained in any theory: it started somewhere else and moved there. The temperature at that distance is about 520 degrees C, and with solar wind it would be impossible for a small core to accrete that much gas. (The planet has a density of less than 1, so like Saturn it would float if put in a big enough tub of water.) How would it move? The simplest way would be if we imagined a Jupiter and a Saturn formed close enough together, when they could play gravitational billiards, whereby one moves close to the star and the other is ejected from the system. There are other plausible ways.

That leaves the question of how the planet forms in the first place. To get so big, it has to form fast, and there is evidence to support such rapid growth. The planet LkCa 15b is around a star that is slightly smaller than the sun, it is three times further out than Jupiter, and it is five times bigger than Jupiter. I believe this makes our sun special – the accretion disk must have been ejected maybe as quickly as 1 My. Simulations indicate that oligarchic growth should not have led to any such oligarchic growth that far out. My explanation (given in my ebook “Planetary Formation and Biogenesis”) is that the growth was actually monarchic. This is a mechanism once postulated by Weidenschilling, in 2004 (Weidenschilling, S., 2004. Formation of the cores of the outer planets. Space Science Rev. 116: 53-56.) In this mechanism, provided other bodies do not grow at a sufficient rate to modify significantly the feed density, a single body will grow proportionately to its cross-sectional area by taking all dust that is in its feed zone, which is augmented by gravitation. The second key way to get a bigger planet is to have the planetary accretion disk last longer. The third is, in my theory, the initial accretion is chemical, and the Jupiter core forms like a snowball, by water ice compression fusing. Further, I argue it will start even while the star is accreting. That only occurs tolerably close to the melting point, so it is temperature dependent. The temperatures are reached very much closer to the star for a dwarf. Finally, the planet forming around a dwarf has one final growth advantage: because the star has a lower gravity, the gas will be drifting towards the star more slowly, so the growing planet, while having a less dense feed, also receives a higher fraction of the feed.

So, in my opinion, apart from the fact the planet is so lose to the star, so far there is nothing surprising about it at all, and the mechanisms for getting it close to the star are there, and there are plenty of other “star-burning” planets that have been found.

Why has the monarchic growth concept not taken hold? In my opinion, this is a question of fashion. The oligarchic growth mechanism has several advantages for the preparation of scientific papers. You can postulate all sorts of initial conditions and run computer simulations, then report those that make any sense as well as those that don’t (so others don’t waste time.) Monarchic growth leaves no real room for scientific papers.