Based solely on the inner planets, what relationship is evidenced between crust thickness and proximately to the Sun? A. The greater the distance from the Sun, the thicker the crust. B. None of the above. C.The closer to the Sun, the thinner the crust. D.The closer to the Sun, the thicker the crust.

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anonymous · Answer

The answer they probably wanted isn't the correct answer. The correct answer is none of the above and I'll tell you why: Mercury has a crust between 100 km and 300km http://en.wikipedia.org/wiki/Mercury_%28planet%29 Venus has a hard to determine crust thickness (because the atmosphere pressure and composition interferes with instruments used to measure remotely). Also the atmosphere is extremely hot and corrosive, making probes that would try to land on the surface. What we can say is the Venus is very active volcanically, sizable eruptions are occurring pretty much non-stop. http://en.wikipedia.org/wiki/Venus Earth has a crust that is approximately 35 km thick, a part of the lithosphere (which is 60 km thick). Earth's crust is definitely thinner than mercury's. http://en.wikipedia.org/wiki/Earth It has to be B or D from evidence gathered from our probes (keep in mind we've never studied Mercury's subsurface geology in detail, so the truth is we don't know as well as we should, it's an educated guess) But D scientifically speaking is bogus for a number of reasons. Mainly that the thickness of a crust, or any crust for that matter only partly has to do with the distance from the central star and more to do with radioactive decay (aka. fission nuclear reactions) going on in the core of the planet (or moon). True, the closer to the star the more intense light and thereby the warmer things are on the surface. But for solid planets (as opposed to gas giants), the sunlight doesn't penetrate very far. Take caves for example, which are often only a kilometer or less below the surface, they are COMPLETELY dark without a light source you take with you. The light doesn't go through rock (well neutrinos and gamma radiation can somewhat, but that's not relevant here and is getting off-topic). Proof? Take Jupiter's "moon" Io for example (which is close to the size of one of the inner planets), it's pretty far away from the sun but one of the MOST volcanically active places in the entire solar system. The sunlight is pretty weak (low intensity) out at this distance, and most surfaces (you would think) should be sub-zero frozen. The presence and composition of an atmosphere has a lot to do with it. Without an atmosphere things get very cold at night, extremely so, and excessively hot in the day. Yet Io stay hot all the time an erupts constantly. So... The heck? Yeah none of the above, Io is an exception to the rule of thumb that being further away from the central star in a solar system (our sun) means it going to be colder. If there's an exception to the rule, you have to account for that.