Mercury is the closest planet to the sunand the eighth largest.Mercury is smaller in diameter than Ganymedeand Titanbut more massive.
Orbit:57,910,000 km (0.38 AU) from sun
Minimum Distance From Sun:45.9 million km (28.5 million Miles)
Maximum Distance From Sun:69.7 million km (43.3 million Miles)
Minimum Distance From Earth:45 million km (28 million Miles)
Rotation period about axis:58.65 days
Revolution perioud about the sun:0.24 years
Tilt of axis:Zero degree
Surface Gravity:3.7 m/s^2(0.38 X EARTH'S)
Temperature Range on Mercury:-184 C to 427 C
Average Surface Temperature:440 K
Name in Roman/Greek Mythology:Mercury/Hermes
Mercury has been visited by only one space craft,Mariner 10.it flew by three times in 1974 and 1975.Only 45% of the surface was mapped(and,unfortuatly,it is too close to the sun to be safely imaged imaged by HST) and you have to know that the images taken by Mriner10 are the only close up images we have of the planet's surface.and nasa will send the messenger (the Mercury surface,Space Environment,Geochemistry and Ranging)to mercury in 2004.
Mercury's orbit is so close to the sun that is difficult to see from the ground.This explains why some early astronomers never saw the planet.Viewed from Earth,Mercury is never far from the sun in the sky.Because of the glare of the sun,it can only be seen in twilight.
Mercury's orbit is highly eccentric;at perihelion it is only 46 million km from the sun but at aphelion
it is 70 million.
The perihelionof its orbit precesses around the sun at very slow rate .19th century asironomers made very careful observation of Mercury's orbital parameters but could not adequately explain them using newtonian mechanics.
difference between the observed and predicted values were a minor but nagging proplem for many decades.It was thought that another planet(sometimes called vulcan)might exist in an orbit near Mercury's to account for discrepancy.
The real answerd turned to be much more dramatic:Einsten's general theory of Relativity,its correct prediction of the motions of Mercury eas an important factor in the early acceptance of the theory.
Untile 1962 it was thought that mercury's Day was the same length as its Year so as to keep that same face to the sun much as the moon does to the earth.But this was shown to be false in 1965 by doppler rader observation.It is now known that Mercury rotates
three times in two of its years.
Mercury is the only body in the solar system known to have an orbital/rotational resonance with a ratio other than 1:1.
This fact and the high eccentricity of Mercury's orbit would produce very starnge effects for an observer on Mercury's surface.At some longitudes the observer would see the sun rise and then gradually increase in apparent size as it slowly moved toward the zenith.At that point the sun would stop,briefly reverse course,and stop again before resuming its path toward the horizon and decreasing in apparent size.
the while the stars would be moving three times faster across the sky.observers at other points on Mercury's surface would see different but equally bizarre motions.
" Timocharis " made the first recorded observation of Mercury in 265 BC.Other early astronomers that studied Mercury include Zupus(1639),who studied the planet's orbit.
Because it is so difficult to make out features on the surface of the planet from Earth,it was not until the 1960s that scientists determined the correct day length rate (59 Earth days) of the planet on its axis.This also showed that Mercury's day length and year are the same.
Mercury's surface& core:-
Mercury is in many ways similiar to the Moon:its surface is heavily cratered and very old it has no plate tectonics.On the other hand,Mercury is much denser than the Moon(5.43 gm/cm^3 vs 3.34).
Mercury is the second densest major body in the solar system,after Earth.Actually Earth's density is due in part to gravitational compression;if not for this,Mercury would be denser than Earth.
This indicates that Mercury's dense iron core is relatively
larger than Earth's,probably comprising the majority of the planet.Mercury therefore has only a relatively thin silicate mantle and crust.
Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km.the silicate outer shell (analogous to Earth's mantle and crust) is only 500 to 600 km thick.At least some of the core is probably molten.
The surface of mercury exhibits enormouse escarpments,some up to hundereds of kilometeres in length and as much as three kilometers high.Some cut thru the rings of craters and other features in such a way as to indicate that they were formed by compression.
It is estimated that the surface area of Mercury shrank by about 0.1%(or a decrease of about 1 km in the planet's radius).
One of the largest features on Mercury's surface is the caloris basin;it is about 1300 km in diameter.It is thought to be similar to the large basins on the Moon.Like the lunar basins,it was probably caused by a very large impact early in the history of the solar system.
that impact was probably also responsible for the odd terrain on the exact opposit side of the planet.
In addition to the heavily cratered terrain,Mercury also has regions of relatively smooth plains.Some may be the result of ancient volcanic but some may be the result of the deposition of eject from cratering impacts.
Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind.because Mercury is so hot,these atoms quickly escape into space.
thus in contrast to the Earth and venus whose atmosphere are stable,Mercury's atmosphere is constantly being replenished.
A reanalysis of the Mariner data provides some preliminary evidence of a recent volcanism on Mercury.But more data will be needed for confirmation.
Amazingly,radar observation of Mercury's north pole (a region not mapped by Marine10) show evidence of waterice in the protected shadows of some craters.
Mercury has a small magentic field whose strength is about 1% of Earth's.
Mercury's densityis nearly as high as Earth's.Yet in most other respects it more closely resembles the moon.Did it lose its light rocks in some early catastrophic impact?
No trace of iron has been seen in soectroscopic studies of Mercury's surface.Given its presumably large iron core this is very odd.Is Mercury much more completely differentiated than the other terrestrial planets?
what processes produced Mercury's smooth plains?
Are there any surprises on the other half of the surface we've not seen?low resolution radar images obtained from Earth show no surprise,but you never know.
It is the difficulties which face MAN now and can't answer for it and from our site "Our Solar System" encourage youth to answer about it by studying and searching not by waiting.
And by the messanger which will lunch in 2004 we may know more about Mercury.
AND WE DO NOT KNOW MAY BE WE WILL LIVE IN MERCURY.
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Last Modified : 5 Sep. 2001
Created By#C0115361 Team