Is science sometimes in danger of getting tunnel vision? Recently published ebook author, Ian Miller, looks at other possible theories arising from data that we think we understand. Can looking problems in a different light give scientists a different perspective?

Planetary Formation Update - April

My ebook, "Planetary Formation and Biogenesis" was first published on Amazon 1 year ago, it argues that quite a lot of the standard theory needs rethinking, in particular that initial accretion is dependent on chemistry, not gravity, and while I have found a number of otherwise puzzling observations for the standard theory, as far as I can tell, nothing I have found contradicts my propositions. Readers may forgive me, but I find that rather satisfying. Part of the reason, of course, might be that the year has been relatively quiet regarding discoveries. That will change, because it is inevitable that sooner or later a large number of papers will come out regarding findings from Curiosity. That will be far more critical as far as my ideas go. A further possibility is that the theory is somewhat elastic, and hence difficult to falsify. That is true in some ways. There are a number of options for planets, but once one is chosen, there are very specific consequences. Unfortunately, some of those are as yet too difficult to test, which may also be why the theory has survived!
The most interesting evidence came from the Kepler satellite. It discovered (Science 340: 262) that Kepler 62 has five planets that range from half to twice Earth's diameter. These are at 0.715, 0.427, 0.12, 0.929, 0.055 A.U., around a star of 0.69 times the sun's mass. It is estimated that the outer one is in the centre of the habitable zone, and the next inner one possibly. The problem then is, are these truly rocky planets or ice planets sent inwards according to one of the possible mechanisms proposed? If they are all rocky planets, and were spaced according to my "expectation prediction" (which requires the star to have accreted at a rate proportional to its stellar mass squared, which in turn is observed, but only loosely, so there should be a range from the expectation position) the typical planet equivalents should be Mars-type  0.58, Earth-type 0.328, Venus-type (if there is one, and this is somewhat flexible) 0.22, Mercury-type 0.12. (This also assumes the secondary accretion rate, critical for exactly how the rocky planet evolves, was similarly scaled to our star, and observational evidence shows a possible order of magnitude deviation each way.) If the outer one is the Earth-type, then the theory predicts that accretion was significantly faster, and any Venus-type should be at 0.47 A.U., and  Mercury at 0.22 A.U. and there should be a Mars-type at about 1.14 A.U. Additional inner planets (Vulcans, which are predicted to be Mercury-like) would seem unlikely as the temperatures would grow too hot over a shorter radial difference. If the 0.427 A.U. planet is an Earth-type, then accretion was slower, and more material was available, in which case the Mars-type should be at about 0.68 A.U., the Venus-type at about 0.28 A.U., and the Mercury-type at 0.15 A.U. This agreement is not too bad, and the slower accretion rates could permit Vulcans. On the other hand, some of these bodies could be quite different, without violating the theory because if the accretion is slow, a variety of additional options might arise. Their densities should define their nature.
Slower stellar accretion rates permit planetary bodies to grow bigger, at which point they interact chaotically. It is generally considered that one major body (Theia) collided with Earth and formed the Moon. However, it is possible that modest-sized bodies might have collided and retained much of their structure provided collisions were not too violent. There is evidence this occurred (Science 340: 22-24). The Earth's deep mantle behaves as if there are two major piles of different composition, one below Africa and one mainly below the South Pacific. Plumes rise from the edges of these and give rise to the volcanic islands. These piles are thousands of kilometers across, but their composition remains unknown. An important point is that these "piles" are denser than much of the remaining mantle. Within my proposition, this is suggestive that they accreted closer to the star than the bulk of the Earth, which increases the pyroxene content, they differentiated, then eventually collided with Earth. The increased density arises through shedding aluminosilicates during collisions, including shedding them to Earth's crust. Is that right? That is unknown, but it is an interesting thought, at least for me.
Posted by Ian Miller on May 6, 2013 4:08 AM Europe/London

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