Venus: Our Sister Planet?
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Venus is known as the jewel of the sky. It was thought to be two different planets by ancient astronomers and thus referred to as the morning star and the evening star. Early astronomers also referred to Venus as Earth’s sister planet. Both are considered young planets due to the low number of craters and both are similar in size, and their chemical compositions are similar. The surface of Venus has many features, which are similar to the Earth such as canyons, volcanoes, lava flows, rift valleys, mountains, craters, and plains. The comparisons basically end there.
Venus differs from the Earth in many ways. The one big difference that I noticed was the surface temperature of the planet. It reaches a surface temperature of 900° F. This is hotter than Mercury, which is closer to the sun. This temperature is hot enough to melt lead. This higher temperature is attributed to a runaway greenhouse effect caused by the heavy atmosphere of carbon dioxide. This would also probably account for the lack of water on the planet. The oceans, if there were ever any, were probably boiled away millions of years ago. The extremely hot temperature also attributes to the fact that no life forms have been found on Venus.
Venus makes one trip around the sun faster than it can rotate once. It takes 225 Earth days for Venus to orbit the Sun and it takes 243 days for it to rotate once. A Venusian day is longer than a Venusian year. It also rotates in the opposite direction than the Earth. The Sun would rise in the west and set in the east if observed from Venus. “In addition, the periods of Venus’ rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach.” (1)
85% of the surface of Venus is covered with volcanic rock. Most of the radar images of Venus indicate many high mountains, which appear to be volcanic in origin. Radar images indicate evidence for recent volcanic activity on Venus. I guess this would also be a contributing factor to the high concentration of carbon dioxide in the atmosphere. This could also contribute to the thick cloud layer surrounding the planet. These clouds are composed of sulfuric acid. Strong winds in the upper atmosphere push these clouds around Venus once every four days. There is very little wind on the surface of the planet. These thick clouds make it impossible to se the surface of the planet. That is why most imagery of the planet is from radar. Most of this imagery was done in the 1990s over a 4-year period by the Magellan orbiter.
Venus has an extremely weak magnetic field, which is usually attributed to its slow rotational period. Venus also has no satellites (moons). The pressure of the atmosphere of Venus is 90 times greater than that of Earth.
Another interesting note is that there are no small craters on Venus. Its dense atmosphere causes small meteoroids to burn up prior to reaching the surface. The craters that are formed are usually in bunches indicating that large meteoroids break up prior to impact.
Venus is considered a terrestrial planet, just like Mars, Mercury and Earth because it has solid rocky surfaces. This type of surface would remind you more of our moon than of our green and blue Earth. The number of differences far out weigh the similarities between Earth and Venus. Early astronomers referred to Venus as our sister planet because of its proximity and its similar size. I guess if we crank up the temperature here on Earth a little bit and create our own runaway greenhouse effect, this planet will look a bit more like Venus. We would boil our oceans away; all vegetation and life would be burnt away to reveal our rocky surface. Volcanic activity would increase. This would cause the sulfur in the atmosphere to increase. More sulfur in the atmosphere means more clouds. More clouds would give Earth the same appearance from distance planets as Venus.
Being that both our planets were formed millions of years ago from the same nebula, I guess it was the luck of the draw that Earth developed the way it did. It would have a bit more interesting if Venus had developed in a similar way and was able to sustain life. The runaway greenhouse effect seems to have been the determining factor in how our planets have evolved. So as we look to the early morning or early evening sky and see the brightest star, we can always wonder what might have been.