Why We Cannot Get Evidence of Alien Life Yet

We have a curiosity about whether there is life on exoplanets, but how could we tell? Obviously, we have to know that the planet is there, then we have to know something about it. We have discovered the presence of a number of planets through the Doppler effect, in which the star wobbles a bit due to the gravitational force from the planet. The problem, of course, is that all we see is the star, and that tells us nothing other than the mass of the planet and its distance from the star. A shade more is found from observing an eclipse, because we see the size of the star, and in principle we get clues as to what is in an atmosphere, although in practice that information is extremely limited.

If you wish to find evidence of life, you have to first be able to see the planet that is in the habitable zone, and presumably has Earth-like characteristics. Thus the chances of finding evidence of life on a gas giant are negligible because if there were such life it would be totally unlike anything we know. So what are the difficulties? If we have a star with the same mass as our sun, the planet should be approximately 1 AU from the star. Now, take the Alpha Centauri system, the nearest stars, and about 1.3 parsec, or about 4.24 light years. To see something 1 AU away from the star requires an angular separation of about one arc-second, which is achievable with an 8 meter telescope. (For a star x times away, the required angular resolution becomes 1/x arc-seconds, which requires a correspondingly larger telescope. Accordingly, we need close stars.) However, no planets are known around Alpha Centauri A or B, although there are two around Proxima Centauri. Radial velocity studies show there is no habitable planet around A greater than about 53 earth-masses, or about 8.4 earth-masses around B. However, that does not mean no habitable planet because planets at these limits are almost certainly too big to hold life. Their absence, with that method of detection, actually improves the possibility of a habitable planet.

The first requirement for observing whether is life would seem to be that we actually directly observe the planet. Some planets have been directly observed but they are usually super-Jupiters on wide orbits (greater than10 AU) that, being very young, have temperatures greater than 1000 degrees C. The problem of an Earth-like planet is it is too dim in the visible. The peak emission intensity occurs in the mid-infrared for temperate planets, but there are further difficulties. One is the background is higher in the infrared, and another is that as you look at longer wavelengths there is a 2 – 5 times coarser spatial resolution due to the diffraction limit scaling. Apparently the best telescopes now have the resolution to detect planets around roughly the ten nearest stars. Having the sensitivity is another question.

Anyway, this has been attempted, and a candidate for an exoplanet around A has been claimed (Nature Communications, 2021, 12:922 ) at about 1.1 AU from the star. It is claimed to be within 7 times Earth’s size, but this is based on relative light intensity. Coupled with that is the possibility that this may not even be a planet at all. Essentially, more work is required.

Notwithstanding the uncertainty, it appears we are coming closer to being able to directly image rocky planets around the very closest stars. Other possible stars include Epsilon Eridani, Epsilon Indi, and Tau Ceti. But even then, if we see them, because it is at the limit of technology, we will still have no evidence one way or the other relating to life. However, it is a start to look where at least the right sized planet is known to exist. My personal preference is Epsilon Eridani. The reason is, it is a rather young star, and if there are planets there, they will be roughly as old as Earth and Mars were when life started on Earth and the great river flows occurred on Mars. Infrared signals from such atmospheres would tell us what comprised the atmospheres. My prediction is reduced, with a good amount of methane, and ammonia dissolved in water. The reason is these are the gases that could be formed through the original accretion, with no requirements for a bombardment by chondrites or comets, which seemingly, based on other evidence, did not happen here. Older planets will have more oxidized atmospheres that do not give clues, apart possibly if there are signals from ozone. Ozone implies oxygen, and that suggests plants.What should we aim to detect? The overall signal should indicate the temperature if we can resolve it. Water gives a good signal in the infrared, and seeing signals of water vapour in the atmosphere would show that that key material is present. For a young planet, methane and ammonia give good signals, although resolution may be difficult and ammonia will mainly be in water. The problems are obvious: getting sufficient signal intensity, subtracting out background noise from around the planet while realizing the planet will block background, actually resolving lines, and finally, correcting for other factors such as the Doppler effect so the lines can be properly interpreted. Remember phosphine on Venus? Errors are easy to make.

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Terraforming Mars

In the 1990s, there was much speculation about terraforming planets, particularly Mars. The idea was that the planet could be converted into something like Earth. To make Mars roughly like Earth, the temperature has to be raised by about ninety Centigrade degrees, atmospheric pressure has to be raised by something approaching a hundred times present pressure, and a lot of water must be found. That presumably comes from buried ice, so besides uncovering it, an enormous amount of heat is required to melt it. The reason Mars is colder is that the sun delivers half the power to Mars than Earth, due to Mars being further away. The gas pressure depends on two things. The first is there has to be enough material, and the second is we have to get it into the gas phase. The most obvious gas is carbon dioxide, because as dry ice, it could be in the solid state, but would be amenable to heating. The problem is, if carbon dioxide is present with a lot of water, it will be absorbed by the water, particularly cold water, and slowly turned into material like dolomite. Nitrogen is the major gas in our atmosphere, but that would be a gas on Mars, and there is very little in the Martian atmosphere.

Why did anyone ever think Terraforming was possible? One reason may be that about 3.6 Gy ago (a gigayear is a thousand million years) it was thought that there were huge rivers on Mars. The Viking images found a huge number of massive river valleys, and so it was thought there had to be sufficient temperatures to melt the water. Subsequent information has suggested that these rivers did not persist over a prolonged wet period, but rather there were intermittent periods where significant flows occurred.  Such rivers probably never flowed for more than a million years or so, and while a million years might seem to be an extremely long period to us, it is trivial in the life of the solar system. Nevertheless the rivers meandered for that period, which is at least suggestive that they were relatively stable for that time, so what went wrong?

When I wrote Red Gold, I needed the major protagonist to make an unexpected discovery to expose a fraud, and it was then that I had an idea. The average temperature on Mars now is -80 degrees C, and while we could imagine some sort of greenhouse effect warming the early Mars, the sun only emitted about two-thirds the energy it does now, so temperature would have been a more severe problem. To me, it was inconceivable that the temperature could get sufficiently above the melting point of ice to give significant flows, but there is one way to make water liquid at -80 degrees C, and that is to have ammonia present. If the volcanoes gave off ammonia as well as water, that would give some greenhouse gas, and the carbon would be present as methane, this being what is called a reducing atmosphere. Sunlight tends to act with water to oxidize things, giving off hydrogen that escapes to space. This has happened extensively on Mars, indeed at many sites where chloride has been deposited on the surface, it has been converted to perchlorate. So methane would oxidize to carbon dioxide, and carbon dioxide would react with ammonia to make first, ammonium carbonate, then, given heat or time, urea. So my “unexpected discovery” was the fertilizer that would make the settlement of Mars possible. I had something that I thought would make my plot plausible.

Funnily enough, this thought took on a life of its own; the more I thought about it, the more I liked it, because it helps to explain, amongst other things, how life began. (The reduced form of nitrogen is a set of compound called nitrides. Water on nitrides, plus heat, makes ammonia, and also cyanide, which is effectively carbon nitride.) Standard theory, of course, assumes that nitrogen was always emitted as the nitrogen gas we have in our atmosphere. Of course you might think that all the scientists are right and I am wrong. Amongst others, Carl Sagan calculated that if ammonia was emitted into the atmosphere, it would be removed by sunlight in a matter of a decade or so, and he had to be right, surely? Well, no. Anyone can be wrong. (Of course you may say some, such as me, are more likely to be wrong than others!) However, in this case I maintain that Sagan was wrong because he overlooked something: ammonia dissolves in water at a very fast rate, and in water it will be protected to some extent. To justify that, we have found rocks on Earth that are 3.2 billion years old and that have samples of seawater enclosed, and these drops of seawater have very high levels of ammonia. These levels are sufficiently high that about 10% of Earth’s nitrogen must have been dissolved in the sea as ammonia at the time, and that is after the Earth had been around for about 500 million years after the water flowed on Mars.

If anyone is interested in why I think this occurred, Red Gold has an appendix where my first explanation is given in simple language. For those who want something a bit more detailed, together with a review of several hundred scientific papers, you could try my ebook, Planetary Formation and Biogenesis.

Red Gold: a unique book (in a very minor way)?

A claim to be unique requires some extraordinary evidence, but I think I can back that up. Red Gold is a futuristic novel about the colonization of Mars, and there is nothing extraordinary about that, indeed there are many others out there.  No, the claim for uniqueness is based on something far more unusual. The backstory in the novel was in the near future when I wrote it, and in the event, what I wrote came to pass, with me as the “player”, and it was not what I intended. Let me explain.

Red Gold was written in the early to mid 1990s, and was set in 2075-76. The setting was the colonization of Mars, but the story was more about the disintegration of a relationship between two nominal business partners when one learns that the other is creating a massive stock-market bubble on Earth with fraudulent Martian stock (or shares, depending on where in the world you are). To expose the fraud, I needed “a totally unexpected discovery”. Further to my concept of putting science in fiction, I had explained that the “soil” on Mars is very deficient in nitrogen, and there is very little in the atmosphere as well. Accordingly, feeding people in the long term might be difficult. This gave me the inspiration for the “unexpected discovery”: One of the protagonists could find the nitrogen fertilizer needed to make Martian settlement viable in the long term. So I wrote in that the main character took drilling equipment to the very bottom of Hellas Planitia, which happened to be owned by the protagonist, and many of the drill samples found urea.

Why was it a surprise? Well, standard scientific theory said the required ammonia in the early atmosphere could not have been present. My solution was to invent a minor scientist, Pavel Marchenko, who had predicted a reduced atmosphere in the early 21st century, but his papers were variously rejected by the mainstream scientific journals, and eventually the theory was published in an extremely obscure place and promptly forgotten.

Red Gold eventually made it to an editor’s desk in a serious publishing house, but it was rejected as too implausible (actually by another editor who was clearing a desk, after the first one died). I got somewhat irritated to have my science trashed by a literary editor, even if it was originally presented “tongue in cheek”, so I became involved. The more I looked into the nature of Mars, the more certain I was that my argument was sound. Furthermore, it made predictions, one of which was, of course, that the early lakes on Mars may have accumulated ammonia, which would react with carbon dioxide to form urea. The ammonia solved the major problem of how water can flow on Mars when the temperatures never reached the melting point of ice. So, I worked away at this and eventually formed a proper theory. It was then that I fulfilled the destiny: the papers were rejected as either not being compelling, or, in one case, because I did not do computer modeling.

To be fair, there was a fundamental problem; scientific papers are rather brief, and usually establish one point. Unfortunately, this analysis is based on the intersection of sets of data, and no single point is compelling. To gradually build up the case you need a book, not a paper. There was a further problem. Carl Sagan showed that, because of sunlight, ammonia in the atmosphere only lasts decades, although he noted that screening chemicals could prolong that. The problem with that is, ammonia will largely be dissolved in water, where it is more protected. Irrespective of what various scientists believe, one sample of seawater has been found on Earth containing water from when the Earth was 1.3 billion years old, and this sample had sufficient ammonia in it that about 10% of all nitrogen on Earth was in that form. If that can happen on Earth, surely it could happen on Mars as well.

I eventually tired of the rejections and self-published the theory as my ebook “Planetary formation and biogenesis”, which the scientific community would definitely consider to be obscure. There is one minor point I did not fulfill: after various pointless rejections (I could not resist throwing the odd barb) Marchenko published in Armenian. That I could not do! My guess is, I shall further fulfill the backstory: my theory will be thoroughly ignored.

I think that is unique, but I could be wrong. Let me know if you think I am. Meanwhile, if this piques your interest, there is a free download at Amazon for November 16-18.