Our Solar System .... Mercury.
Mercury was named by the Romans after the fleet-footed messenger of the gods because it seemed
to move more quickly than any other planet.
It is the smallest planet in the solar system. Its diameter is 40% smaller than Earth and 40% larger than the Moon.
It is even smaller than Jupiter's moon Ganymede and Saturn's moon Titan.
If an explorer were to step onto the surface of Mercury, he would discover a world resembling lunar terrain.
Mercury's rolling, dust-covered hills have been eroded from the constant bombardment of meteorites.
Fault-cliffs rise for several kilometres in height and extend for hundreds of kilometres.
Craters dot the surface. The explorer would notice that the Sun appears two and a half times larger than on Earth;
however, the sky is always black because Mercury has virtually no atmosphere to cause scattering of light.
As the explorer gazes out into space, he might see two bright stars.
One appearing as cream coloured Venus and the other as blue coloured Earth.
Before Mariner 10 , little was known about Mercury because of the difficulty in observing it from Earth telescopes.
At maximum elongation it is only 28 degrees from the Sun as seen from Earth. Because of this,
it can only be viewed during daylight hours or just prior to sunrise or after sunset.
When observed at dawn or dusk, Mercury is so low on the horizon that the light must pass through 10 times
the amount of Earth's atmosphere than it would if Mercury was directly overhead.
Mariner 10 in 1974/1975 has been the only spacecraft to have by-passed Mercury and most of our detailed information
has come from just 3 active passes this spacecraft made before contact was lost.
Mercury was found to have virtually no atmosphere.
Less than half of the surface has been imaged, so our knowledge of Mercury’s topology is very incomplete.