Mercury and Venus

Mercury

The innermost planet is rarely seen
because of the Sun's glare. With  less
than half Earth's gravity, Mercury retains only a wisp of an atmosphere  (presumed to be helium). The lack of a
significant atmosphere allows  temperatures
to fluctuate from 750 degrees Fahrenheit during the day to  minus 320 Fahrenheit at night.

Like the other terrestrial planets
-- Venus, Earth and Mars -- Mercury is  made
mostly of rock and metal. This small world is scarred by craters and  looks somewhat like our Moon.

Mercurius: roman
winged messenger of the gods 

Historical notes

Mercury has been known since ancient
times. Its elusiveness generated  the
name Hermes, given by the Greeks, later translated to Mercurius by  the Romans.

Venus

The second planet from the sun bakes
under twice as much solar  radiation as
Earth and reaches temperatures of 895 degrees Fahrenheit  (480 degrees Celsius). Pressure from the dense
atmosphere of sulfuric  acid gas is about
95 times greater than Earth's and would crush a human.   The thick cloud cover around Venus rotates
much faster than the planet  itself --
once every four days. After the moon, Venus is the brightest object  in the sky.  

The surface of Venus is mostly a
rocky desert (this computer-generated  view
shows lava flows around Sif Mons). Like Mercury, Earth and Mars,  Venus is composed of mostly rock and metal.  

Venus: roman
goddess of love and beauty 

Historical notes

The Greeks believed Venus was two
separate objects -- one in the  morning
skyand another in the evening. Because it is often brighter than  any other object in the sky -- except for the
sun and moon -- Venus has  generated many
UFO reports.  

Final facts

While all of the planets orbit in an
ellipse, Venus' orbit is the closest to a  perfect circle. It is the only planet in the
solar system whose day (241 Earth  days)
is longer than its year (225 Earth days).