What would an exoplanet look like if you landed on it?

Your intrepid space explorer lands on an alien planet. What would it look like? For practical reasons, in series like Star Trek, they looked somewhat like Earth, or occasionally some other planet in our solar system. Is this realistic? I am going to say, yes, with one or two reservations. The first is, our intrepid explorer lands. By definition, that excludes “water worlds” and giants. From our lists of exoplanets, giants are rather common, although this may also be because they are the easiest to find.

In previous posts, I discussed the possibility of forming planets suitable for alien life, specifically at: http://wp.me/p2IwTC-3e , http://wp.me/p2IwTC-3g , http://wp.me/p2IwTC-3k , http://wp.me/p2IwTC-3n . To summarize these posts, if planets are formed, then at least initially all stellar systems form the same sort of planets. Most importantly, my theory suggests star formation is aided by planetary formation because while the star contains most of the mass, the planetary systems contain most of the angular momentum, and a transfer of angular momentum makes transferring material to the star easier. The general consensus is that the disk gases should sweep accreting bodies into the star, but that will not happen if the gas transfers its angular momentum to the planet, and I suggest there is a mechanism by which this could happen, and in my opinion it is the easiest way to transfer angular momentum from gas to planet.

In standard theory, all planetary formation commences with the formation of planetesimals, and these then form planets through gravitational attraction, collisions getting more and more violent. There is only one thing wrong with that theory: while it has been around for about seventy years, nobody has a clue how the planetesimals are formed to start with. In my theory, outlined in my ebook Planetary Formation and Biogenesis, initial planetary accretion occurs through chemistry, including physical chemistry, and such chemistry changes with temperature, and hence specific types of planets occur at specific temperatures. Accordingly, each different zone forms planetary systems that are chemically different, at least in their cores and satellites. The giants, of course, acquire gas from the accretion disk by gravity. Our solar system is of only moderate probability, because the evidence is our system formed and growth was then stopped through an early T Tauri disk cleanout, when the star shoots out very strong winds that sweep away the accretion disk. If the accretion disk is longer lived, as more than half will be, planets get bigger, are more likely to form gas giants, then they start playing gravitational billiards when they get big enough. This gravitational billiards is also more likely to occur around red dwarfs because the systems become more compact, and closer together makes gravitational interactions stronger. Each different planet has a different basis for forming, it has a different chemical composition (although the great bulk of rocky planets comprises silicates) and so each planet in our system may have an equivalent in other systems where the size of the planets are moderate. That means our intrepid space explorer would see planets similar to ours.

Of course, care has to be taken with “similar”. The positions of the planets depend on the temperatures in the accretion disk, which also depends on the rate of stellar accretion so the positions of predicted planets will vary considerably. Also, how much variation in semimajor axis there might be for a given planet around a specific star is unclear, but it certainly will not be precise. On the other hand, the habitable zone depends only on the size and age of the star, and so an equivalent planet may have quite significant differences in stellar distance. Without that uncertainty, the zone that forms Earth only overlaps neatly with the habitable zone for stars similar to our sun, i.e. G type stars and the heavier K type stars. As noted in a previous post http://wp.me/p2IwTC-5y , the planets in the habitable zone around the red dwarf Kapteyn’s star should correspond to Jupiter and Saturn in composition. Because such planets largely form through ices, such planets would be “water worlds” and our intrepid explorer could not “land” in the usual meaning of the word.

One comment about Venus. My conclusion was that rocky planets do not accrete gases from the disk, because any such gases are essentially removed by the violent solar winds around an early star. Accordingly, the necessary materials must be accreted as solids, and water is essentially accreted by attraction to silicates, and in particular, aluminosilicates that can act as cements. Carbon is accreted either as a carbide, or as a pyrolytic char on silicates during the heated stage. Nitrogen has to be accreted as nitrides, and the materials for life, and the atmosphere, are generated by the action of water on these solids as the planet heats up. Does this matter? Well, in my opinion, yes. Have you seen threats that Earth could have a runaway greenhouse effect and end up like Venus? Well, if I am correct, there was no runaway greenhouse effect as such and the Venusian oceans were never boiled off. There was never much water accreted by Venus, and what was there was used to make the atmosphere. The excess deuterium on Venus did not arise through photolysis of water (which actually stops once the oxygen forms a protective ozone layer) but from the chemical isotope effect, which is a much stronger means of enhancing deuterium concentrations. The oxygen in the Venusian water is now there in the carbon dioxide atmosphere, and with no excess water, Venus could not fix its carbon dioxide.

Having formed this theory, naturally I use it, and in my ebook Scaevola’s Triumph, to be published on September 30, when Scaevola is in a force about to attack an occupied planetary system, and when the issue of “which planets are important” arises, the Venus equivalent is dismissed as “the usual hell planet”. The other two rocky planets are more interesting, and I shall mention them in a later post.

Finally, one correction to a previous announcement. Because Scaevola’s Triumph, is the third in a trilogy, I have offered a promotion on the first two (Athene’s Prophecy and Legatus Legionis) on Amazon, running from October 3-6. However, this is restricted for the time being to Amazon.com. The reason: I priced them at $2.99, and the UK price was fixed proportionately. Thanks to currency changes, the UK price drifted 2p below that where a discount could be offered, so I had to raise the price by 2p so I could lower it! Having done that, it told me I had republished, so I had to wait 30 days! Work out the logic here. I shall offer the promotion in due course.

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