The next 10 days are very exciting ones for cosmologists and physicists, as NASA's Messenger probe - launched in August 2004 - will begin the first of three fly-bys of the enigmatic planet Mercury, a series designed to culminate in an orbit around the planet on 18 March 2011, after a journey of 5 billion miles. This first fly-by, scheduled for January 14, will be the first close up look at Mercury since Mariner 10 completed its third and final rendezvous in 1975. 

Technology has moved on apace in the last 30 years and planetologist hope to learn a lot more this time. Astronomers think that the planet holds a secret that will reveal how the solar system was formed. Mercury is an oddball planet and if science can explain how it came together it would go a long way to explaining how the other planets formed.

Mercury is especially dense, suggesting it has a huge iron core amounting to 40% of the planet's total volune. This is a huge proportion compared to Earth's 17%. It is sepculated that one of the enormous asteroids that hurtled around the early solar system crashed into it and blasted a way much of the rocky outer mantle, leaving it about half its original size. There will be clues as to its history in the composition of the surface material, and Messenger will be using spectroscopy to measure the relative amounts of minerals such as iron oxide, silicon dioxide, and magnesium oxide.

Mercury also has a weak magnetic field (just 0.1% of the Earth's field). Such fields are usually generated in the core of a planet by a circulating region of  electrically conducting molten material, but Mercury's core should have solidified long ago, putting an end to any magnetic field.

But for me the most interesting measurements will be those concerned with verifing (or not) Einstein's General Theory of Relativity which predicts that that space is 'curved' in the immediate vicinity of massive objects such as the sun. In the case of Mercury, its elleptical orbit means that is should dip into the 'dent' in space as it passes close to the sun. The net result should be that the planet travels an extra 70 thousand kilometres, and this has already been allowed for in Messenger's route. The question being asked is whether relativity is accurate enough or is there another effect that needs to be taken into account. This effect would be due to the (so far theoretical) energy field that is needed to explain the accelerating expansion of the universe.

 Cosmologists wait with baited breath for the first verification of this hypothetical energy field that must have operated since the beginning of time, and further evidence that the universe began with a Big Bang, when 'God created the heavens and the earth'.

 Mark your calendar - January the 14th 2008.

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