VENUS

NASA Image of Venus     Venus is the second closest planet to our Sun at an average distance 67 million miles.  It revolves around the Sun every 225 Earth days, but its rotation takes 243 Earth days.  One other interesting note is that Venus rotates clockwise, the only planet in our solar system to do so, and contrary to its own orbit around the Sun.  Research suggests that the "backward" rotation is caused by tides which are raised in the thick atmosphere by the Sun, and with friction interaction between the atmosphere and planet itself.  It is hypothesized that these interactions caused Venus's rotation to slow, stop, and then reverse.  This is somewhat similar to what is happening here on Earth, as our Moon's pull on our oceans causes tides whose subsequent friction is gradually slowing Earth's rotation.  Other recent research suggests that Venus' clockwise rotation was produced by an extreme impact from a large body early in Venus' development, 4 to 5 billion years ago (similar to how a major impact created our Moon from Earth).  This large impact on Venus may have resulted in the planet reversing its rotation if the blow was from the opposite direction of its rotation.  Venus is one of only three planets in our solar system which has a perfect circular sphere (the other two being Mercury and Pluto).

Atmosphere and Weather:  Venus has a thick atmosphere made up almost entirely of carbon dioxide.  It also exerts a pressure 92 times higher than the earth's, resulting in a pressure-cooker environment.  Venus is covered by dense clouds made up primarily of sulfuric acid.  The clouds are so thick it is impossible to see its surface without using sophisticated radar systems.  Imaging radar systems aboard the NASA space probes Pioneer (1978) and Magellan (1990-1994) produced a map of the Venusian surface.  These systems also detected lightning, hypothesizing that the lightning is generated in thick clouds around 35 miles above the surface.  The surface is desolate and continent like features exist complete with canyons, mountains, plains and waterless oceans.  The Venusian surface is pock-marked with a low number of large craters along with volcanic rock and lava flows.  It appears that over 85% of the surface is covered by volcanic rock with giant lava flows having flooded areas producing the plains.  Research suggests that some of these volcanoes have erupted within the past few centuries and there is evidence that the entire planet was "resurfaced" three to five hundred million years ago.      

Venus false color image/NASA The incident visible and infrared spectrum from the Sun are major contributors to the extremely hot temperatures on Venus, with the dense, carbon dioxide atmosphere not letting the infrared rays escape back into space.  These temperatures resemble something more of a raging fire due to an uncontrolled greenhouse effect which more than doubles the temperature on the planet's surface.  It appears that the surface temperature ranges from about 820 degrees to nearly 900 degrees F.  The average surface temperature is 847 degrees F., hot enough to melt lead.  No wonder the ocean basins are "dry".  At these temperatures any water would evaporate nearly instantaneously.  However research from NASA's Ames Research Center suggests that liquid water in the oceans and seas were prevalent on Venus for hundreds of millions of years in earlier times.  Due to Venus' immense pressure, water could have existed with temperatures as warm as 200 to 300 degrees F.  But that is still likely too hot to have sustained any primitive life forms.  As Venus continued to warm, any liquid water was boiled off into the atmosphere.  

The Pioneer Spacecraft in December 1978 revealed very high winds aloft in its atmosphere, approaching speeds of 200 mph.  Along with the thick cloud cover, this could explain why the night side of the planet has temperatures nearly the same as the day side, as strong winds aloft transfer heat around the globe.  However it appears that the surface winds are very light. 

In short, Venus is by far the hottest planet in our solar system, with a very minimal diurnal temperature spread.

 

QUICK FACTS
(Data is from NASA Goddard)

Average distance from Sun 67,000,000 miles
Perihelion 66,600,000 miles
Aphelion 67,500,000 miles
Sidereal Rotation 243 Earth days
Length of Day 116.75 Earth days
Sidereal Revolution 225 Earth days
Diameter at Equator 7,504 miles (only about 5% smaller than Earth's)
Tilt of axis 177.4 degrees
Moons None
Atmosphere Carbon Dioxide 96.5%, Nitrogen 3.5% 
Discoverer Unknown
Discovery Date Prehistoric

DEFINITIONS:

Average distance from Sun:  Average distance from the center of a planet to the center of the Sun. 
Perihelion:  The point in a planet's orbit closest to the Sun.
Aphelion:  The point in a planet's orbit furthest from the Sun. 
Sidereal Rotation:  The time for a body to complete one rotation on its axis relative to the fixed stars such as our Sun.  Earth's sidereal rotation is 23 hours, 57 minutes.
Length of Day:  The average time for the Sun to move from the Noon position in the sky at a point on the equator back to the same position.  Earth's length of day = 24 hours
Sidereal Revolution:  The time it takes to make one complete revolution around the Sun.
Axis tilt:  Imagining that a body's orbital plane is perfectly horizontal, the axis tilt is the amount of tilt of the body's equator relative to the body's orbital plane.  Earth is tilted an average of 23.45 degrees on its axis.


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