MERCURY
CLASSIFIED INFORMATION
Mercury
is the closest planet to the Sun. It is also the smallest planet besides Pluto.
It has a diameter of 3,031 miles (4,878 km) across
its equator. There are moons in our solar system bigger than Mercury.
Mercury got its name from the Romans as the Messenger God because of its speed. Mercury completes one full orbit of the Sun every 88 Earth days. Because Mercury has an elliptical orbit, its speed is constantly changing. When Mercury is closest to the Sun, perihelion, it is only 28,500,000 miles (45,865,000 km) from it. At aphelion, when it is farthest from the Sun, it is 43,300,000 miles (69,680,000 km) away.Mercury moves so quickly around the Sun that at times we can see it both during the early morning and late at night. The Sun's gravitational pull has a great affect on Mercury's speed. At perihelion, the planet travels so fast that it overtakes its planetary rotation, causing, if any one were standing on Mercury, to seem as if the Sun would slow down, stop, and go backwards for awhile before repeating the process and then returning to normal. Mercury has the second most eccentric orbit out of all the planets, behind Pluto.
Mercury is a member of the four rocky inner planets also known as terrestrial planests. It is the smallest of the terrestrial planets and the closest to the Sun. Mercury has no atmosphere but does have a thin layer of helium gas surrounding the planet. Although this layer of helium gas is just enough to fill a small balloon. Calculations by scientists say that Mercury is very dense for its size. Its core is larger in proportion to its overall size than to all the other inner planets made of heavy metals. Its density is 11,990 pounds per cubic yard (5,440 kilograms per cubic meter) which means it is 5.44 times as dense as water. Because of its closeness to the Sun it would be believed that only the most heat resistant elements could survive on Mercury where they would sink to the core to explain Mercury's large core. But this is not the case. For this reason scientists have speculated that at one time, during the early formation of the rocky, inner planets, Mercury was hit by an asteroid. This asteroid would have stripped away the outer layers of a thick mantle and Earthlike crust, leaving a reduced outer layer surrounding the core. This would explain Mercury's extra large core. Today, Mercury now mainly consits of core, with a thin rocky silicon crust. Mercury is composed of small amounts of helium, neon, and argon.
You would think that Mercury would be the hottest planet because of its closeness to the Sun, but it isn't. It isn't because of its poor "thermal inertia". Thermal inertia is the time taken to absorb and conduct heat recieved from the Sun. Mercury's is poor because it lacks an atmosphere to keep the heat in. Although it has a poor thermal inertia, Mercury is hot. It can reach 660 degrees F (350 degrees C) at the equater. The face of Mercury that faces the Sun recieves ten times as much solar energy than the moon. But the side that does not face the Sun, and because of thermal inertia, can have temperatures plumit to -275 degrees F (-170 degrees C).
The
surface of Mercury is covered in an uncountable amount of craters, mostly
from meteorites. The lack of an atmosphere can explain this. Mercury has some
smooth surfaces that were made by large craters being filled up with molten
materials more than 3,000,000,000 years ago.
There is one crater that is a Mercury "hot spot". It is a truely
gigantic crater named the Caloris Basin. Its diameter is 840
miles (1,350 km) and has rings of mountains surounding it as if thrown
up as shock waves that extend another 625 miles (1,000
km) outward. The youngest of Mercury's numerous craters have ray-like
streaks shooting outward from their centers and are therefore called "ray
craters." Mercury does have some interesting surface characteristics.
These include the "lobate scarps",
which are long ridges that as long as 300 miles (483
km) and as high as two miles (3.2 km)
high. The shrinking of the planet's metalic core could of caused these. Mercury
does have a magnetic field that reveals an active molten core creating rotation
currents.
Year Length . . . . . . . . . . . . . . . . . . 88 Earth days
Day Length. . . . . . . . . . . . . . . . . . . 59 Earth days
Temperature (sunlit side). . . . . . . . . . 660 degrees F (350 degrees C)
Temperature (dark side). . . . . . . . . . .-275 degrees F (-170 degrees C)
Average Distance from Sun . . . . . . . . 36,000,000 miles (58,000,000 km)
Diameter across equater . . . . . . . . . . .3,031 miles (4,878 km)
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Credits: Photographs; "Courtesy Jet Propulsion Laboratory. Copyright (c) California Institute of Technology, Pasadena, CA. All rights reserved. Based on government-sponsored research under contract NAS7-1260."