Statistics:
- Planet Diameter: 12,104 km, 0.948 Earth Diameters
- Planetary Mass: 4.92x1024 kg, 0.82 Earth masses
- Average Distance from Sun: 108 million km, 0.7233 AU
- Length of Day: 243 Earth days*
- Length of Year: 225 Earth days
- Atmosphere: Very thick, mostly carbon dioxide & sulfuric acid
- Day/Night Surface Temperature: > 480 degrees Celsius
History of Observations
The Venusian Atmosphere
Space Probes to Venus
History of Observations:
Venus has always been an object of intense interest to many cultures. It appears in our evening sky either just before sunrise or after sunset, and it has aptly been named the "Morning Star" or "Evening Star" accordingly. In ancient times, as today, Venus commonly appears to be the brightest object in the sky next to the Sun and Moon. This feature flared the curiosity of many who would eventually study this object in greater detail. However, what the ancients did not know was that Venus was not really a star like the other objects in the night sky, but it is a planet instead.Among the first real detailed observations of Venus were those performed by Galileo Galilei in the early 17th century. Galileo turned a small terrestrial telescope towards Venus and recorded the phases of Venus; this was some of the first evidence that Venus was another planetary body, like our own Earth. One of the things that he noticed was that Venus was obscured by a cloudy haze, and no real surface features were apparent. This layer of cloud cover would obscure the Venusian surface until the mid-20th century.
Venus' Atmosphere:
Spectrographic studies of Venus' atmosphere performed here on Earth revealed that the Venusian atmosphere is composed of mostly carbon dioxide gas (96%), nitrogen gas (<4%), oxygen gas (<1%), and trace amounts of water vapor. In addition, a great deal of the Venusian cloud cover that is commonly observed in visible light is composed of sulfuric acid droplets. Therefore, due to this interesting information about the seemingly impenetrable atmosphere of Venus, ' some interesting projections were made as to what the surface of Venus might be like. In this century, there were a variety of proposals as to what the surface of Venus would be like. Some scientists claimed that the surface was a great, vast swamp covered with thick vegetation while others guessed that the surface was covered in deserts and seas of boiling oil. It ends up that neither of these viewpoints was accurate.Because the surface of Venus is enshrouded in a thick layer of carbon dioxide atmosphere, much of the incoming solar radiation incident upon the planet is trapped in what scientists Carl Sagan and James Pollack dubbed a greenhouse effect. What happens is that visible light from the Sun penetrates the atmosphere of Venus, warms up the surface, and the surface then re-emits radiation as infrared light, which is trapped by the heavy clouds. Thus, the heat is effectively trapped and so the surface of Venus warms up. Radio emissions measurements and calculations yielded that the surface of Venus is at a whopping 750 K (900 F or 480 C); this is hot enough to melt solid lead!
Planetary Probes to Venus:
Since the mid-1960's Venus has been explored by numerous robotic probes launched by both the United States and former Soviet Union. In 1970, the Soviet probe Venera 7 descended to the surface of Venus, and it ceased transmitting data only 23 minutes later. The surface conditions on Venus were so hostile that the probe was rendered non-operational; the information returned was valuable... it ends up that the surface pressure is 90 times that of Earth's surface atmospheric pressure. In 1972, Venera 8 landed on the Venusian surface and was able to return information for a total of 50 minutes. In 1975, Venera 9 landed upon the surface and returned the first pictures of the surface of another planet to Earth.
Two more Soviet probes, Veneras 11 and 12, gathered information concerning the weather of Venus. Among other things, they discovered that certain regions of Venus (now believed to be highly volcanic in nature) were concentrated regions of lightning activity. Veneras 13 and 14 landed upon the surface and determined that the rocks at the landing sites were volcanic in nature; thus, it was becoming slowly apparent that Venus has a very active volcanism.
In August of 1990, the United States probe Magellan placed itself into an orbit about Venus. The primary mission of Magellan was to perform detailed radar-mapping of the surface of Venus. Radar is necessary to use because it is a wavelength of light that will both penetrate the cloud cover and be almost totally reflected back through the atmosphere to the orbiter.
In the radar map shown above, red features indicate higher elevation whereas blue regions indicate lower elevations. Note that the coloring is to indicate elevation only; i.e., blue should not be mistaken for water! Also, the areas in grey indicate a lack of data. Many interesting surface features were revealed by Magellan's investigations. Among these are the lack of craters due to meteorite impacts, massive lava flows, and active volcanos.
