Wednesday, May 11, 2011

Meet the planets: Venus

Venus is the second planet from the Sun and the closest to Earth in terms of size (often referred to as Earth’s “sister” or “twin” planet). It is the brightest planet visible to the naked eye outside of our own Earth-Moon system, and so has been observed since ancient times.

Because it is brightest near dusk and dawn, Venus is often called the “Evening Star” or “Morning Star,” and many ancient cultures originally thought that there were indeed two different heavenly bodies. Ancient names for the planet include “Ishtar” (Babylonian) and “Aphrodite” (Greek), both goddesses of love, and “Anahita” (Persian), a fertility goddess. The official name comes from the Roman goddess of love and beauty (Latin: Venus). Alternate names still in use in many parts of the world include variations of “Al-Zuhra” (Arabic), “Sukra” (Sanskrit) and “Star of Gold” (Chinese). Venus is also nicknamed the “Cloud Planet” because of its dense atmosphere.

In his novels, C.S. Lewis said that the Venusian natives called their planet “Perelandra,” while fellow writer Edgar Rice Burroughs claimed it was “Amtor.” They were both wrong.

Description

Venus is a size-F (large terrestrial) planet with a mean diameter of 12,104 km (7,521 miles), about 95% of Earth’s diameter. Its mass is about 81.5% of Earth’s, while its surface area and gravity are about 90% of Earth’s. Like the other terrestrial planets, it has a differentiated interior (likely a metal core surrounded by silicate rock), although the exact nature of Venus’ interior is not known with certainty. Due to its slow rotation, Venus’ core does not generate a protective magnetic field, which would help it retain water and protect it from the Sun’s radiation. The inability to retain water makes Venus’ crust so dry that there are no plate tectonics (the shifting that causes earthquakes), although Venus does appear to be volcanically active.

About 80% of Venus’ surface is smooth, volcanic lowland plains. The remaining surface consists of two highland “continents.” The northern continent is called Ishtar Terra and is about the size of Australia. It contains Venus’ highest peak, Maxwell Montes. The southern continent is called Aphrodite Terra and is roughly the size of South America.

Venus has an incredibly dense atmosphere (92 times the pressure of Earth's at the surface) composed primarily of carbon dioxide. The air pressure on Venus is equal to the water pressure about 1 km below the surface of Earth’s oceans. This atmosphere causes a runaway greenhouse effect that makes Venus’ surface the hottest in the Solar System, with consistent temperatures of about 460°C (860°F) over the entire planet.

The cloud cover on Venus makes the sky looks reddish orange, and the clouds are so thick that no stars or planets can be seen. Dim light from the Sun can be seen, but the Sun itself cannot be discerned. If the Sun could be seen from the surface, it would appear about twice as big and twice as bright as it does on Earth. Mercury would appear brighter than on Earth, becoming the “Morning Star” and “Evening Star” to Venus, just as Venus is to Earth (although not quite as bright). Brighter still, though, would be the Earth itself, as from the perspective of Venus, the sunlit side of both Earth and its Moon would often be in full view. Venus does not have any natural satellites of its own.

Venus rotates in the opposite direction of all the other planets, causing the Sun to rise in the west and set in the east. It also rotates very slowly, with a day on Venus lasting about 117 Earth days. (It actually takes Venus even longer, 243 Earth days, to rotate, but its backwards rotation works together with its orbital motion to make the same side of the planet face the Sun a little bit quicker.) A year on Venus is about 225 Earth days.

Venus’ orbit around the Sun is the closest to being perfectly circular of any major planet (eccentricity 0.0068). Its distance from the Sun only varies between 0.718 and 0.728 AU, with the average being 0.723 AU (about 108 million km or 67 million miles). Venus is also one of the least tilted on its axis (only 2.6° after factoring for its retrograde rotation). Combined, the two facts mean that there is very little seasonal variation on the planet.

Humans

Because telescopes could not penetrate its heavy cloud cover, Venus remained shrouded in mystery until very recently. Beginning in the 1960s, unmanned U.S. and Soviet spacecraft managed to unlock some of the planet’s secrets, including its temperature and atmospheric pressure, but it wasn’t until NASA’s Magellan mission (1989-1994) that the Venusian surface was finally mapped in detail. Future exploration is being planned and may shed more light on our strange “sister planet” over time.

Its size and location make it a prime target for human colonization, but major technological hurdles must first be overcome. Terraforming the planet will at a minimum require removing most of the carbon dioxide atmosphere, reducing the surface temperature, and introducing oxygen and water. It would also likely involve creating a protective magnetosphere and establishing a more Earth-like day-length of approximately 24 hours, as opposed to the current 117 Earth days.

The first colonies will be floating, self-contained cities high in the Venusian atmosphere, where temperatures and air pressure are more manageable. These will serve as bases for the population involved in terraforming efforts. A giant solar shield will be placed in Venus’ relatively stable L1 Lagrange point, where it could be maintained between Venus and the Sun with minimal effort, deflecting solar radiation and thus cooling the planet. Mass drivers will eject some of the dense atmosphere. If done right, this and other techniques will also speed up the planet’s rotation, eventually decreasing day length until it is roughly equal to Earth and Mars. Provided Venus's core is still molten, this will have the added benefit of creating a different spin rate between the surface and the interior, thus generating a magnetosphere.

As the temperature and atmospheric pressure drop, hydrogen will be imported en masse from Saturn or one of the other gas giant planets, and combined with the remaining carbon dioxide to form water and elemental carbon. In the end, oceans will cover up to 80% of the surface, and some of the remaining atmosphere will dissolve into them, further reducing pressure. When the temperature and water content are right, algae and various plant life will be introduced, which will convert much of the remaining carbon dioxide (and smaller amounts of carbon monoxide) to breathable oxygen. Sulfur (and the resultant sulfuric acid rain) will be removed from the atmosphere and rendered safe by similar chemical processes.

Enclosed surface colonies will begin at this time, tending crops and putting the finishing details on the planet. Eventually, as air quality improves, these colonies will transition to partially-enclosed, air-quality-controlled tented communities, and then finally to completely open settlements. A host of Earth animals will be introduced, from bees to whales, completing the transformation into a sustainable ecosystem.

Ongoing attention will be required to maintain the solar shield, which by the end will have been modified to let through about 50% of the Sun’s light and heat, equal to what Earth receives. (The Sun will still look twice as big in the sky on Venus, but it will only be half as bright.) If a magnetosphere proves unattainable, the solar shields and atmosphere will provide adequate protection against radiation, but large quantities of hydrogen will have to be imported periodically to replenish what is lost to space and ensure that the planet doesn’t dry out. However, with these measures in place, the Venusian environment will become the most Earth-like in the Solar System – our true twin planet at last.

Aliens (speculative)

There was a time, about 65 million years ago, when Earth was seen as undesirable real estate, the redneck trailer park to Venus’ gated community. The dominant species on the planet were the Cythereans, an intelligent, humanoid people. They were approximately the size and build of humans, save for their long necks, which made them about a head taller. Despite this, their physiology was very different than Earth mammals, being closer to a cross between a shark and a potato.

Their smooth, waxy skin was a pale, bluish-green color. They were entirely hairless except for some leafy, feather-like growths atop their heads and on their limbs, and the color patterns of these were the only obvious difference between males and females of the species. Their “bones” were made of a semi-rigid cartilage-like material, and their internal structure did not contain large organs, but rather a cork-like tissue intersected by the small, redundant “nodes” of various systems: circulatory, respiratory, etc. (In this way, a single individual may have over 100 different, tiny “hearts,” for example.)

Cytherean society was quite advanced for the time, and they enjoyed comforts like clockwork robotic miniature dragon servants and steam-powered flying vehicles. Unfortunately, they were vain creatures and the Martians finally had enough of them. It was a war that would destroy both civilizations. (And kill the dinosaurs back on Earth, but that’s another story.)

Some Cythereans managed to survive the devastation. Realizing that their war machines had doomed their environment, but unwilling to leave their once-fair world, they built giant, lava-proof crystal chambers deep underground. There, the best of their species lie still, in extra-dimensional suspended animation, waiting for someone to clean up the place. Meanwhile, a select few stayed behind as caretakers, and over the generations their descendants have mutated into a completely different species, at once more advanced and more primitive than their predecessors.

These neo-Cythereans have lost the feathers and developed thicker skin (resembling the rind of a cantaloupe) to withstand the intense pressure. They no longer have long necks, or indeed any necks whatsoever. Save for a small amount of cartilage that still gives some shape to their heads and faces, their skeletal system has shrunk to almost nothing, unneeded now that their bodies are grafted to cybernetic suits. Underground, they have become part of a closed-loop food chain, feeding off the milk and meat of the chicken-goats, which feed off the droppings of the squirrel-owls, which eat the oyster-lilies that grow in the soil fertilized by dead Cythereans. Because of the limited space and food resources in their underground world, they have become a disciplined society bound by strict codes. For example, they have tied their very existence to their sacred duty as caretakers, limiting their own population to the same number of Cythereans remaining in hibernation (originally over 100,000, but now estimated at only 20,000). If a population imbalance arises – a new baby is born, or a hibernation capsule fails – a lottery is held and the losers must fight to the death to restore the balance.

If and when we terraform Venus, there will be severe implications for both groups of Cythereans. There will be culture shock not only with the humans, but also between the two different groups of natives, whose languages no longer even resemble each other. Expect the ancient Cythereans to be grateful at first, but soon start acting like they own the place. Meanwhile, the neo-Cythereans will need to be given a new cosmic purpose in life (or, at the very least, some vocational training), as well as basic assistance in physically adapting to the new planetary conditions.

Images courtesy of NASA, Ittiz and Pedro Silva.

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