Sunday, May 06, 2007

Mercury. The first planet from the sun, laying at a distance of 0.3871 au from Sol, about 1/3rd of the distance from the Sun to Earth. Mercury has a diameter of 4,878 km, once more about 1/3d of the diameter of Earth but a mass of only 5.53% that of our planet. Its gravity is only about 28.4% that of the Earth, and its year is only about 88 days. Its rotation, however, is slower. A Mercurian day is about 59 Earth days. It's this rotation that is important in the latest discovery about Mercury. As reported in the May 4th edition of Science magazine, the journal of the AAAS, a team of astronomers from Cornell University measured small twists in the planet's rotation. They did this by sending a radio signal to reflect off the planet from a station at Goldstone, California and catching the signal again at another station in Green Bank, West Virginia.Other signals were also sent from the Arecibo Observatory in Puerto Rico and analysed at Goldstone. Their conclusion after 5 years of observation was that their values were twice as large as they would be if Mercury's core was solid. Jean-Luc Margot of Cornell states that they have a 95% confidence level in their results which are best interpreted as the result of Mercury having at least a partially molten core.
This explains the results of the flyby of Mariner 10 thirty years ago which detected a small magnetic field around the planet, something that simply couldn't occur if the planet had a solid core. The speculation is that lighter elements such as sulphur are present in Mercury's core in amounts substantial enough to lower its melting point enough to produce a magma. This challenges the standard model of planet formation which says that the terrestrial planets such as Mars, Earth, Venus and Mercury formed from heavier elements with high melting points that condensed near to the Sun while the outer planets formed in zones where lighter elements could condense. The speculation that explains this anomaly is that there was some sort of "mixing" in the early solar system whereby planetesimals carrying lighter elements were transported into the inner solar system where they were part of planet formation.
Mercury will be studied further when NASA's Messenger spacecraft makes its first flyby in 2008.
Mercury (Greek- Hermes) was the messenger of the gods and patron of merchants, messengers, lawyers and thieves. Only the "messengers" don't fit in the above lot. It solar facing surface is about 400 degrees centigrade while the far side is -170 degrees. Worse than a Manitoba day. The very eccentric orbit of Mercury and its high variation in speed would produce some strange effects if you were standing on the surface (with nuclear sunblock of course). The Sun would be seen to rise, stop, back up and set in the east, rise again, move to the west, set again, rise in the west and finally set in the east. Seems like the Sun can't make up its mind.
Mercury presently cannot be viewed, but it will appear again in the evening sky after the sun sets in late May and early June.

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