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 - May

For May, once again there were few significant papers (at least that I found) that impinge on theories of planetary formation, and I shall restrict myself to the two closest. A commonly measured variable is isotope enhancements, and Halliday (Nature 497: 43-44) showed that lunar basalts have slightly higher levels of heavy iron than Earth, which is itself significantly enhanced in heavier isotopes compared with Mars or Vesta, however there is no enhancement for heavier isotopes in lithium. What does that mean? Interpreting such results is a common problem, because what we are trying to do is to get whatever we can from the very limited samples available to us. The temptation then is to look at the current model and fit the data to it, and if it makes sense within that model, than that is how the data are interpreted. We tend to assume that isotope enhancements only arise through vaporization/condensation, but there are alternative ways of enhancing heavier isotopes, such as the chemical isotope effects. In short, such enhancements may reflect greater processing of a sample.
 
Another interesting paper came from Hamano, Abe and Genda (Nature 497: 607 – 610). They classified rocky planets according to their distance from the star. A type 1 planet forms beyond a critical distance and solidifies within several million years and if the planet acquired water during formation, it retains it. A type 2 planet lies within the critical distance, and can maintain a magma ocean for up to 100 My because the steam atmosphere (assuming it acquired water) blankets the planet, and incoming radiation from the star exceeds the radiative ability of the atmosphere to emit sufficient heat to cool the surface (~ 300 W m-2). Hydrodynamic escape dessicates type 2 planets. Venus is on the border of the critical distance, but is classified as Type 2 because of its properties. The argument depends on there having been a magma ocean in the first place, and it only applies to water emitted at the very beginning. On Earth, volcanism has been emitting volatiles continuously, and while most are secondary now, some remain primary. The point is, most volatiles have yet to be degassed at 100 My. On Mars, it appears to have taken up to 500 My before the bulk of the water was degassed, by which time their mechanism is irrelevant. Of course, what they tried to do was work out why Venus is like it is. My argument is that there are alternative interpretations to the data, and in the case of Venus, it never had much water on the surface.
 
Meanwhile, for those interested in some of the issues relating to planetary formation and the origin of life, there is currently a forum operating on the web. Go to https://astrobiologyfuture.org/forum . Amongst other things, people are more prepared to ac=knowledge what we do not know, and more prepared to be speculative, than in scientific papers.
Posted by Ian Miller on Jun 3, 2013 4:19 AM Europe/London

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