Venus Goddess of Love

Venus is the far easier planet to observe. Its brilliant white color led the ancient Greeks to name it in honor of their goddess of love. Venus' brilliance comes from the reflection of light from those thick white clouds, which cause the planet to reflect some 80% of the sunlight, which falls on it. It comes closer to Earth than any other body in the solar system except the Moon. It is very nearly identical to Earth in size, measuring 12,103 kilometers in diameter. It is remarkably similar to Earth in density and mass. It was thought for centuries that Venus was a twin of Earth. But for the entire age of the telescope, its surface has been a mystery to us because it is shrouded in clouds. Spectrographic analysis gave us the first sign that Venus is very different from Earth. Venus' atmosphere turns out to be about 96% carbon dioxide and exerts pressures on the surface equal to 90 times that on the surface of Earth. This combination of pressure, cover and carbon dioxide drives temperatures on the surface to levels around 500 degrees Celsius (932 degrees Fahrenheit). That temperature is sufficient to melt lead and other soft metals. That combination of temperature and pressure makes even robotic exploration of the surface incredibly difficult. Though four Russian built spacecraft have made it to the surface intact and returned pictures, all expired after less than two hours. American spacecraft have observed the planet from orbit. The Pioneer Venus 1 orbiter made the first global radar map of the surface in the late 1970s. In the early 1990s, the Magellan probe improved dramatically on the resolution produced by Pioneer Venus 1. In fact, the Magellan maps are so good they are an order of magnitude better than any produced for any application on Earth, at least until the Shuttle Radar Topography Mission of 2000. It was a common joke among astronomers during the decade between those two missions that if you were going to get lost in the solar system do it on Venus. It has better maps. So some four hundred years after Galileo first observed Venus through his telescope, we know how the surface is shaped and contoured, but it still remains a mystery what the surface is made of and what helped shape it. Many of Venus' surface features appear to be sculpted by volcanism. Magellan radar images show indications of lava flows on the surface in the somewhat recent past. What the source of volcanism is however is different from Earth. Venus does not appear to have any surface plates like Earth has. The crust is all one piece. There are surface features called "rift valleys" that resemble surface plates pulling apart from one another. The East African rift and the Dead Sea are both formed by this process on Earth, by the Eurasian and African plates moving apart. Large valleys on Venus of this same geological type must have been formed by more local activity. It was thought for many years that Venus had no magnetic field but it does appear that Venus does have a very weak field. The planet has an average density of 5.2 grams per cubic cen-timeter,suggesting an Earth-like iron core. The weakness of the field may be related to the slowness of the planet's rotation.

Venus rotates on its axis like all the other planets do, but Venus does two very unusual things. First as viewed from above,Venus rotates retrograde, that is to say that it rotates clockwise rather than the counterclockwise direction that all the other planets do. It also takes longer to complete a rotation than it takes to go around the Sun. A sidereal day on Venus is 243 Earth days long, but the planet requires only 225 Earth days to make one orbit around the Sun. Why this is so is poorly understood. Though there is little empirical evidence to back up any theory, the leading theories available suggest that Venus was formed from two large masses that impacted in such a way so as to almost completely null the rotation rate of the joint mass. Imagine what an analemma looks like on Venus! While the planet rotates slowly, its atmosphere moves quickly at altitude. As strange as the planet's rotation speed is, the planet's orbit is neat and orderly. Venus' orbit is the most nearly circular of all the planets in the solar system.

Weather at Venus also behaves nothing like on Earth. Ultraviolet imagery of the Venusian cloud tops by the Pioneer Venus orbiter shows us that the cloud tops rotate about the planet at speeds of well over 300 kilometers per hour. At that speed, the entire upper atmosphere rotates as a whole around the planet every four days. But winds on the surface are very different. The Venera 9 and Venera 10 landers found during the brief time that they functioned on the surface that winds at surface level are nearly calm and the atmosphere is completely stagnant. The atmosphere is almost completely lacking in water vapor. The dominant feature of Venusian weather is the amazing temperatures. The runaway temperatures are the result of an out-of-control greenhouse effect. Venus appears to have no more in the way of available greenhouse gases than Earth does, but the planet's closer proximity to the Sun appears to be the key difference. Most of Earth's carbon dioxide is bound up in the rocks. Such rocks, like limestone, prevent the gas from flooding the atmosphere. But on Venus the rocks are heated more than on Earth, forcing them to release carbon dioxide to the atmosphere. As the volume of carbon dioxide increases in the atmosphere, the greenhouse effect accelerates to the point that any water that might have been on the surface boiled off into the upper atmosphere. Once there, ultraviolet radiation would break apart the water molecules into hydrogen and oxygen, which then could easily escape the planet's gravity and depart into interplanetary space.

The age of the telescope led us to believe that Venus was a world very much like Earth. The age of space flight taught us that nothing could be farther from the truth. Venus is a world much like hell. Crushing pressures, scorching temperatures and corrosive clouds make it anything but a romantic place.

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