Information on Mercury

    Mercury is actually very much like our moon here on Earth.  It is heavily cratered, very old, and has no plate tectonics.  Mercury, is however, much denser than the moon.  In fact, it is the 2nd densest body in the solar system.  Much of this is probably due to much of it's presumed iron core.  Most likely, it's iron core is 2/3 the size of the planet, so really that is most of Mercury.

    You are probably wondering why the planet was named Mercury.  Well actually, it was named after the Roman god, Mercury, who was the speedy quick messenger of the gods.  It was named that because it was the fastest planet to rotate around the sun.  Mercury has been known since about the time of Sumerians (3000 B.C.). 

    Mercury has actually only been visited by one mission, Mariner 10, which flew by 3 times in 1974 and 1975.  Since it is too close to the sun, the Hubble Space Telescope cannot see Mercury.  So it is the least known planet.  That is why NASA has decided to send MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) to Mercury, when it will make several fly-by's in 2011.  BepiColombo, launched by ESA in cooperation with Japan, will also be launched about the same time MESSENGER is starting it's fly-by's of Mercury.

    Mercury's orbit is highly eccentric; at perihelion it is only 46 million km from the sun, while at aphelion it is 70 million km from the sun.  At perihelion, Mercury moves very slowly around the sun.  During the 19th century, astronomers could not explain what was causing this discrepancy of an orbit using Newtonian mechanics.  It was then figured that there was a 10th planet (Vulcan) that was causing this problem.  However, with many observations, the planet was really never found.  It was actually something that made great sense: Einstein's General Theory of Relativity!  The General Theory of Relativity is really that matter curves space.  Then in turn, objects in the space then move along the lines formed, thus creating their own lines too.

    In the early 1960's, Mercury's day was thought to be the same length as it's year.  This was, however, proven wrong in 1965 by Doppler radar observations that produced the results that it rotates around it's axis 3 times every 2 years.  One of the largest features on Mercury is the Caloris Basin, which stretches 1300 km in diameter!  Mercury also has smooth plains, which were most likely caused by volcanic activity.  Mercury has an extremely small magnetic field, 1% of Earth's.  Reanalyzing Mariner 10 data, there may be frozen water ice at the polar regions of Mercury.  This may have happened because the water would be hidden in the shadow of Mercury.  Temperatures on Mercury can get very extreme.  Average temperatures on Mercury are 800° F and -270° F!  If you were an observer on Mercury, not only would it be very uncomfortable due to the temperature, but the sky would appear black every day except for the sun, stars, and other planets.