Rocky planets, atmospheres and aliens

This week, the second ebook, Dreams Defiled, in my trilogy, First Contact, was published on Amazon. The trilogy is nominally about contact with aliens (at least an alien hologram in A Face on Cydonia) and its consequences. It is also about how civilization might deal with (or perhaps fail to deal with) certain crises that appear to be inevitable. One solution to a crisis that you may or may not like is the proposed solution to the fuels/transport crisis, for no matter what, it is unlikely the whole planet can continue burning energy at the rate some western countries do so now. Check out my solution, and see what you think.

In the meantime, back to the issue of how many planets could have alien life. In previous posts I made an estimate of the likely number of stars that have rocky planets suitable for life. While most stars are not suitable, there are still billions of stars that are, even in this galaxy. The rocky planet then has to be within the right size range. It would have to be somewhat bigger than Mars to ensure it held a significant atmosphere, and there will also be a maximum size, but we do not know what that is. According to my theory, to keep within the right size range, the star has to clear out the accretion disk early, but up to half the stars do this. So, the next question is, will they have water and atmospheric gases? Where do the gases come from?

The usual argument is that the rocky planets get their water and atmospheres through later being bombarded by small asteroids. I don’t believe this either, since, as I show in more detail in Planetary Formation and Biogenesis, since Venus, Earth and Mars have totally different atmospheres, they have to be bombarded selectively by totally different types of asteroids that, as far as we can tell, no longer exist. Thus Venus has about four times as much nitrogen as Earth, but negligible water. Mars has a reasonable amount of water, but almost no nitrogen. How does that come about?

My answer is that the rocky planets form by cement-like dust joining rocks together, and that is where the water comes from. The available cement depends on how hot the solids get during primary stellar accretion, and at what temperature they set during the late cooler accretion disk. Earth happened to set at the optimum temperature – the first stage had been hot enough to get the best cement made, while the second stage was cool enough to let the cement set with the most water. Venus had the same cements, but it was hotter, so it did not set with much water, while Mars had only a limited cement, so while it was cooler, it did not have the means of setting much water. Subsequently, the water reacted with solid sources of carbon and nitrogen and made the atmosphere, and Venus, because it was hotter, had more carbon and nitrogen, so it used up most of its limited water making its very dense atmosphere. If that is true, then most stars that can form rocky planets will have one like Earth in the habitable zone.

That means there are billions of planets in this galaxy capable of forming life. That does not mean that the galaxy is teaming with civilizations. For example, the nearest suitable single star, Epsilon Eridani, is only about 900 million years old. At that age, Earth may or may not have got around to having primitive single-cell life. Of course, in Dreams Defiled I give hints there is a civilization there. How could that be? There is an obvious possibility, but to add to the mystery, I provide evidence that in this fictional story, the food on the rocky planet around Epsilon Eridani and on Earth is each compatible with both life forms, and in general, life forms that evolve separately find that they can only tolerate food that evolved with them.  Now can you guess where this plot is going? As you might guess, I am trying to write stories that also try to impart some scientific knowledge, and which I hope readers will find interesting.

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