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.

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The Fermi Paradox and Are We Alone in the Universe?

The Fermi paradox is something like this. The Universe is enormous, and there are an astronomical number of planets. Accordingly, the potential for intelligent life somewhere should be enormous, but we find no evidence of anything. The Seti program has been searching for decades and has found nothing. So where are these aliens?

What is fascinating about this is an argument from Daniel Whitmire, who teaches mathematics at the University of Arkansas and has published a paper in the International Journal of Astrobiology (doi:10.1017/S1473550417000271 ). In it, he concludes that technological societies rapidly exterminate themselves. So, how does he come to this conclusion. The argument is fascinating relating to the power of mathematics, and particularly statistics, to show or mislead.

He first resorts to a statistical concept called the Principle of Mediocrity, which states that, in the absence of any evidence to the contrary, any observation should be regarded as typical. If so, we observe our own presence. If we assume we are typical, and we have been technological for 100 years (he defines being technological as using electricity, but you can change this) then it follows that our being average means that after a further 200 years we are no longer technological. We can extend this to about 500 years on the basis that in terms of age a Bell curve is skewed (you cannot have negative age). To be non-technological we have to exterminate ourselves, therefore he concludes that technological societies exterminate themselves rather quickly. We may scoff at that, but then again, watching the antics over North Korea can we be sure?

He makes a further conclusion: since we are the first on our planet, other civilizations should also be the first. I really don’t follow this because he has also calculated that there could be up to 23 opportunities for further species to develop technologies once we are gone, so surely that follows elsewhere. It seems to me to be a rather mediocre use of this principle of mediocrity.

Now, at this point, I shall diverge and consider the German tank problem, because this shows what you can do with statistics. The allies wanted to know the production rate of German tanks, and they got this from a simple formula, and from taking down the serial numbers of captured or destroyed tanks. The formula is

N = m + m/n – 1

Where N is the number you are seeking, m is the highest sampled serial number and n is the sample size (the number of tanks). Apparently this was highly successful, and their estimations were far superior to intelligence gathering, which always seriously overestimated.

That leaves the question of whether that success means anything for the current problem. The first thing we note is the Germans conveniently numbered their tanks, and in sequence, the sample size was a tolerable fraction of the required answer (it was about 5%), and finally it was known that the Germans were making tanks and sending them to the front as regularly as they could manage. There were no causative aspects that would modify the results. With Whitmire’s analysis, there is a very bad aspect of the reasoning: this question of whether we are alone is raised as soon as we have some capability to answer it. Thus we ask it within fifty years of having reasonable electronics; for all we know they may still be asking it a million years in the future, so the age of technological society, which is used to base the lifetime reasoning, is put into the equation as soon as it is asked. That means it is not a random sample, but causative sample. Then on top of that, we have a sample of one, which is not exactly a good statistical sample. Of course if there were more samples than one, the question would answer itself and there would be no need for statistics. In this case, statistics are only used when they should not be used.

So what do I make of that? For me, there is a lack of logic. By definition, to publish original work, you have to be the first to do it. So, any statistical conclusion from asking the question is ridiculous because by definition it is not a random sample; it is the first. It is like trying to estimate German tank production from a sample of 1 and when that tank had the serial number 1. So, is there anything we can take from this?

In my opinion, the first thing we could argue from this Principle of Mediocrity is that the odds of finding aliens are strongest on earth-sized planets around G type stars about this far from the star, simply because we know it is at least possible. Further, we can argue the star should be at least about 4.5 billion years old, to give evolution time to generate such technological life. We are reasonably sure it could not have happened much earlier on Earth. One of my science fiction novels is based on the concept that Cretaceous raptors could have managed it, given time, but that still only buys a few tens of millions of years, and we don’t know how long they would have taken, had they been able. They had to evolve considerably larger brains, and who knows how long that would take? Possibly almost as long as mammals took.

Since there are older stars out there, why haven’t we found evidence? That question should be rephrased into, how would we? The Seti program assumes that aliens would try to send us messages, but why would they? Unless they were directed, to send meaningful signals over such huge distances would require immense energy expenditures. And why would they direct signals here? They could have tried 2,000 years ago, persisted for a few hundred years, and given us up. Alternatively, it is cheaper to listen. As I noted in a different novel, the concept falls down on economic grounds because everyone is listening and nobody is sending. And, of course, for strategic reasons, why tell more powerful aliens where you live? For me, the so-called Fermi paradox is no paradox at all; if there are aliens out there, they will be following their own logical best interests, and they don’t include us. Another thing it tells me is this is evidence you can indeed “prove” anything with statistics, if nobody is thinking.

Proxima b

The news this week is that a planet has been found around Proxima Centauri, the nearest star to our solar system. Near, of course is relative. It would take over four years for a radio message to get there, or 40 years if you travel at 0.1 times light speed. Since we can never get anywhere near that speed with our current technology, it is not exactly a find critical to our current society. The planet is apparently a little larger than Earth, and it is in the so-called habitable zone, where the star gives off enough heat to permit liquid water to flow, assuming it has sufficient atmospheric pressure of a suitable composition. That last part is important. Thus Mars and Venus might permit water to flow if their atmospheres were different. In Venus’ case, far too much carbon dioxide; in Mars’ case, insufficient atmosphere, although it too might need something with a better greenhouse effect than carbon dioxide.

Proxima Centauri is what is called a red dwarf. Its mass is about 1/8 of the sun’s, so it gives off a lot less energy, however, Proxima b is only 0.0485 times as far from the star as Earth is, so being closer, it gets more of what little heat is available. The question then is, how like Earth is it?

Being so close to the star, standard wisdom argues that it will be tidally locked to the star, i.e. it always keeps the same face towards the star. So half of the planet is unaware of the star’s presence; one side is warm, the other very cold and dark. However, maybe here standard theory does not give the correct outcome. That it should be tidally locked is valid as long as gravitational interactions are the only ones applicable, but are they? According to Leconte et al. (Science 346: 632 – 635) there is another effect that over-rides that. Assuming the planet does not start tidally locked, and if it has an atmosphere, then there is asymmetric heating through the day, and because the highest temperature is at about 1500 hrs, the heat causes the air there to rise, and air from the cold side to replace it, which leads to retrograde rotation through conservation of angular m omentum. (Prograde rotation is as if the planet went around its orbit as if rolling on something.) Venus is the only planet in our system that rotates retrogradely, and Leconte argues it is for this reason. The effect on Venus is small because it is quite far away from the star, and it has a very thick atmosphere.

Currently, everyone seems to believe that because the planet is in the habitable zone then it will be a rocky planet like Earth. This raises the question, how do planets form? In previous posts I have outlined how I believe rocky planets form, (https://wordpress.com/post/ianmillerblog.wordpress.com/568 and https://wordpress.com/post/ianmillerblog.wordpress.com/576 ). These posts omit the cores of the giants, which in my theory accrete like snowballs. There are four cores leading to giants (Jupiter, Saturn, Uranus and Neptune) and there are four sets of ices to form them. (There are actually potentially more that would lead to bodies much further out.) The spacing of those four planets is very close to the projected ice points, assuming Jupiter formed where water ice would snowball.

Standard theory has it that we start with a distribution of planetesimals about the star, and these attract each other gravitationally, and larger bodies accrete until we get protoplanets, then there are massive collisions. The core of Jupiter, for example, would take about 10 My to form, then it would rapidly accrete gas.

There are, in my opinion, several things wrong with this picture. The first is, nobody has any idea how the planetesimals form. These are bodies as large as a major asteroid. The models assume a distribution of them, and this is based on the assumption all mass is evenly distributed throughout the accretion disk, except that the density drops off inversely proportional to rx. The index x is a variable that has to be assumed, which is fine, and it is then assumed that apart from particle density, all regions of space have equal probability of forming planetesimals. It is the particle density that is the problem. Once beyond the distance of Saturn, collision probability becomes too low to form planets, although the distribution of planetesimals permits Uranus and Neptune to migrate out of the planet-forming zone. Now, for me a major problem comes from the system LkCa 15, where there is a planet about five times bigger than Jupiter about three times further away from a star slightly smaller than our sun that is only 3 My old. There has simply been insufficient time to form that. In my ebook Planetary Formation and Biogenesis I proposed that bodies start accreting in the outer regions similar to snowballs. As the ices are swept towards the star, when they reach a certain temperature the ices start sticking together, and such a body can grow very quickly because as it grows, it starts orbiting faster than the gas. Accordingly, what you get depends on the temperatures in the accretion disk. Unfortunately, for any star we have no idea of that distribution because the disk is long gone. However, to a first approximation, the temperature is dependent on the heat generated less the heat lost. The heat generated at a point would depend on the gravitational potential at that point, which is dependent on stellar mass M, and the rate of flow past that point, which to a very rough approximation, depends on M2. That is by observation, and is + over 100%. So if we assume that all disks radiate equally (they don’t) and we neglect accretion rate variability, the position of a planet depends on M3. That gives a rough prediction of where planets might be, within a factor of about 3, which is arguably not very good.

However, if we use that relationship on a red dwarf of Proxima’s mass, the Jupiter core would be about 0.01 A.U. from the star. In short, Proxima b is at the very centre of where the Saturn equivalent should be, although I think it is far more likely to be the Jupiter core. The relationship is very rough, as the rate of accretion varies considerably from that relationship, and also, as the distances collapse, the size of the star now becomes significant, and back-heating will push the ice point further out. However, what is important here is that this “ice point” is relevant to any accretion theory. If ice is a solid at a given distance, then the ice should be accreted alongside any other solid.

So my opinion is that Proxima b would be a water world, with no land on the surface at all. Further, if it is the Jovian equivalent, it probably will not have an atmosphere, or if it does, it will be mainly oxygen from photolysed water. So I am very interested in seeing the future James Webb telescope aimed at that planet, as water gives a very clear infrared spectrum.

Homochirality – how I believe it originated

In a previous post I issued a challenge that was issued prior to my talk to the Wellington Astronomical Society: can you work out how homochirality arose in life? To remind you, chirality is what causes handedness. If you have gloves, your left hand has its glove and the right hand its, and one cannot really replace the other. Homo chirality means there is one only form of handedness, thus in your body, sugars are D sugars (right handed) while all your amino acids are L, or left handed. The problem is, when you synthesis any of these through any conceivable route given the nature of the starting materials, which have no chirality, you get an equal mix of D and L. On the other hand, if you synthesize the molecules through a chiral entity, chirality remains. Think of using a left-handed glove. If you use it as a mold for a plaster cast, you will keep making casts of left hands, not right hands.

How did nature select one lot and neglect the others? The real reason for asking this, though, was not to do with chirality. Most people can get through life without stopping to worry about why their proteins are made from L amino acids. Space travellers landing on another planet might, though, because if you landed on a planet where all the amino acids were D, then you could not eat their food and be nourished. However we are here. No, the real reason was, this is a chance to show how to develop a theory.

Everyone develops theories, for example, “Who trashed the letterbox?” is an example I gave in my first ebook, which was about developing theories. The book was mainly about scientific theories, so don’t rush out and buy it unless science really interests you, but that point is valid about life. If you look at the web, you can find many places where people theorize on political matters. That would be very good for democracy, if they did it properly, but not so good if the methodology is very bad. Most simply jump to the first conclusion their prejudices lead to, and if that is the way we intend to run our democracy, then we are in trouble. The reason I picked on this issue of chirality is that it is easy, and it is unlikely to run into prejudiced anger and hence can be considered dispassionately.

There are numerous scientific papers devoted to the question of how homochirality arose: they consider the weak force (which does not apply to chemistry anywhere else); materials adsorbed on special clays (without asking how the material can get off again, or why another clay won’t give the complementary material); polarized light (why is there not the opposite result with oppositely polarized light); and even an assertion there is a weak preference in meteorites.
I believe the answer is strangely simple when instead of starting at the beginning with a mixture of both forms, you stop worrying about how it happened, and start asking why it happened? Why would emerging life discard half of the resources available to it? After all, if it did, why did not some other form use both? By using both, it would have twice the amount of resource, so it should be able to survive better, and should prevail.

The obvious answer is that life chose one form because it had to, so where is homochirality so important? The answer is reproduction. What happens is reproduction is governed by nucleic acids that can form a double helix, or duplex. If you have a strand, complementary nucleobases get absorbed on the strand, and if all the bases can link through the phosphate esters, they form their own helix. When that strand is complete, the strands can separate, and the process starts again. That is the essence of reproduction. Now, the problem is in joining those phosphate esters because the appropriate parts have to be in the right place. The new strand has to have the same degree of twist, in the same direction. This is where the chirality comes in. To get a regular twist, or pitch to the helix, all the ribose units have to have the same handedness. Think of making a bolt, and a nut to fit it. If the bolt has right hand thread, then suddenly lurches every now and again into left hand thread, how can you make a nut to fit it?

If a sugar came in with the opposite chirality, the twist would be wrong, the ends would not match up, and the base could not join the strand. It would then go away and nothing would happen until the correct pitch to the helix could be supplied, and that is with the correct chirality of the ribose. At first, strands with any mix could occur, but duplexes would only form with one chirality, and when one came along, since it could reproduce and the others could not, inevitably it must prevail.

Why does that go out to all the other molecules? Because they are made either directly or indirectly from RNA molecules. (RNA is the generator of enzymes.) Accordingly, everything that comes from the chiral RNA will also carry the appropriate chirality.

Was that so difficult to conceive?

Origin of life, and a challenge!

Here is a chance to test yourself as a theoretician. But do not worry if you cannot solve this. Most people will not, and I predict nobody will, but prove me wrong! And as a hint, while nobody actually knows the answer, as I shall show eventually, getting a very reasonable answer is actually relatively simple, although you need a little background knowledge for the first question.

Just before Christmas, I posted with the title Biogenesis: how did life get started?” (http://wp.me/p2IwTC-6e ) but as some may have noticed, I did not get very far along the track indicated by the title. The issue is, of course, somewhat complicated, and it is easier to discuss it in small pieces I also mentioned I was about to give a talk on this early this year. Well, the talk will come on March 4, so it is approaching quickly. Accordingly, I have put out an abstract, and am including two challenges, which readers here may or may not wish to contemplate. Specifically,
1. Why did nature choose ribose for nucleic acids?
2. How did homochirality arise?
Put your guesses or inspired knowledgeable comments at the end of this post. The answers are not that difficult, but they are subtle. In my opinion, they are also excellent examples of how to go about forming a theory. I shall post my answers in due course.

The question of, why ribose, is a little complicated and cannot be answered without some chemical knowledge, so most readers probably won’t be able to answer that. Notwithstanding that, it is a very interesting question because I believe it gives a clue as to how life got underway. RNA is a polymer in which each mer is made up of three entities: one of four nucleobases, ribose and a phosphate ester. The nucleobase is attached to C-1 of ribose (if you opened it up, at the aldehyde end) and the phosphate is at C-5 (the other end, ribose being a five carbon sugar. The nucleobases are, in general, easy to make. If you leave ammonium cyanide lying around, they make themselves, but that is the only thing that appears to be easy about this entity. Sugars can be made in solution by having formaldehyde, which is easily made, react in water with lime, and a number of other solids. That seems easy, except that when you do this, you do not get much, if any, ribose. The reason is, ribose is a high-energy pentose (five carbon sugar) because all the hydroxyl groups are eclipsing each other in the closest orientation (axial, for those who know some chemistry). In the laboratory, double helix nucleobases (duplexes) have been made from xylose and arabinose, and in many ways these have superior properties to ribose, but nature chose ribose, so the question is, why? Not only did it do it for RNA, but the unit adenine – ribose – phosphate turns up very frequently.

Adenine combined with ribose is usually called adenosine, and the adenosine phosphate linkage turns up in the energy transfer chemical ATP (adenosine tripolyphosphate), the reduction oxidation catalysts NAD and FAD, where the AD stands for adenosine diphosphate, and in a number of enzyme cofactors, to give solubility in water. Giving solubility in water is an obvious benefit, but putting a sugar unit on the group would also do that. Giving an electric charge would also be of benefit, because it helps keep the entity in the cell, nevertheless there are also other ways of doing that. You may say, well, it had to choose something, but recall, ribose is hard to make, so why was it selected for so many entities?

The phosphate ester also causes something of a problem. In the laboratory, phosphate esters are usually made with highly reactive phosphorus-based chemicals, but life could not have started that way. Another way to form phosphate esters is to heat a phosphate and an alcohol (including the hydroxyl groups on a sugar) to about 180 oC, when water is driven off. Note that if water is around, as in the undersea thermal vents that are often considered to be the source of life, the superheated water converts phosphate esters to phosphate and alcohol groups. Life did not start at the so-called black smokers, although with sophisticated protection mechanisms, it has evolved to tolerate such environments. Another problem with phosphate is that phosphates are insoluble in neutral or alkaline water, and phosphate esters hydrolyse in acidic water.
However, notwithstanding the difficulty with using phosphate, there is no real choice if you want a linking agent with three functions (two used up to join two groups, one to be ionic to enhance water solubility). Boron is rare, and has unusual chemistry, while elements such as arsenic, besides being much less common, do not give bonds with as much strength.

Homochirality is different matter. (Chirality can be though of like handedness. If you have gloves, your left hand has its glove and the right hand its, even though they are identical in features, such as four fingers and a thumb. The handedness comes from the fact you cannot put those fingers and thumb on a hand where the top differs from the bottom without making the right hand different from the left.) The sugars your body uses are D sugars (think of this as right handed) while all your amino acids are L, or left handed. The problem is, when you synthesis any of these through any conceivable route given the nature of the starting materials, which have no chirality, you get an equal mix of D and L. How did nature select one lot and neglect the others?
Put your guesses below! In the meantime, my ebook, “Planetary formation and biogenesis”, which summarizes what we knew up to about 2012, is going to be discounted on Amazon for a short period following March 6. This is to favour those going to my talk, but you too can take advantage. It has a significant scientific content (including an analysis of over 600 scientific papers) so if your scientific knowledge is slight, it may be too difficult.