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Shrinking planet

13 December 2013

We've had the expanding Earth – now we have shrinking Mercury. This story is at www.scientificamerican.com/article.cfm?id=mercury-is-shrinking-more …. and turns out not to be a big deal in spite of the headline. Studies of Mercury show that it has shrunk over its lifetime (presumed to be 4.5 billion years) but only by 11km. That hardly seems worth making a fuss about but the news and paper were read out at the Fall conference of the AGU and therefore got wide press coverage. As the planet cooled and contracted, it is claimed, it became scarred with long curved ridges like the wrinkles on a rotting apple. I like Cox's Orange Pippins but wrinkly ones – can't say I've noticed furrows. Collapsing apples, when the inside turns to liquid as it rots, and gradually blackens, yes. Anyway, the furrows can't be due to outgassing events as this is a planet – and its solid (or looks solid from the NASA picture gallery), so we have this idea they came about due to cooling – after being incandescent. Do hard rocks, when heated, reform as another hard rock, or do they contract? The argument is that there are more of these steep ridges on Mercury than previously thought – so the amount of shrinkage has been doubled, and more. How different is Mercury to an asteroid?

At http://phys.org/print305977048.html … a short video of a newly discovered asteroid that flew past the Earth on December 11th. It has a speed of 14km a second and this may explain why it was only spotted on December 7th.


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