Was Venus Once Like Earth?

Although Earth and Venus are very similar in size, mass and density, Venus is covered in a thick layer of carbon dioxide and sulfuric acid that traps heat in and leads to extreme warming, which has made the planet much hotter. Average temperatures on Venus average about 800 degrees Fahrenheit. These inferno-like conditions have led some to call it “Earth’s evil twin.”

“Venus and Earth have taken different paths,” says Larry Esposito, a planetary astronomer at the University of Colorado. “But human activity is leading Earth in the same direction [as Venus]. If we can understand Venus history better, we can fine tune our models for Earth.”

Scientists have become increasingly concerned about global warming on Earth due to carbon dioxide, methane and other emissions. As on Venus, this layer of gasses allows radiation to shine through to Earth, but then blocks its reflection back to space. This insulates the planet and leads to warming.

So far efforts to predict global warming for Earth have been inconsistent. Last year, a United Nations group predicted world temperatures could rise by as much as 10.5 degrees or as little as 3 degrees Fahrenheit by the end of the century. A British study released last week predicted a 12.4-degree rise by 2100. A Swiss study, meanwhile, estimated a 7.7-degree rise in the same time frame.

The different predictions could find more agreement with a little more knowledge about Venus. By using Venus as a model of extreme warming and adding detail about the planet into climate models, predictions about Earth’s warming could become more accurate.

“We need to visit Venus and get more information on the atmospheric and surface composition,” says Esposito. “With this fine tuning, we could predict possible feedbacks and extremes which are not evident from what we now know from Earth’s present climate.”

What scientists do know is the second planet from the sun rotates very slowly ? one Venus days equals about 243 Earth days. We also know that the rotation of Earth is slowing down a tiny bit, due to the buildup of carbon dioxide in the atmosphere. The atmosphere of Venus, which contains the only known traces of water at the planet, is made up of mostly carbon dioxide and whips around the planet about 30 miles above its surface at speeds of up to 220 miles an hour.

Explorations of Venus in the 1970s and ’80s were the first to reveal that Earth’s twin wasn’t quite as similar to our planet as it seemed to be at first. The early orbiters detected the shockingly hot temperatures and active volcanoes on the planet’s surface. A more recent, NASA’s Magellan, revealed that the whole face of Venus had recently undergone a dramatic geological change. “The more we found out the less we understood,” says Donald Turcotte, a geophysicist at Cornell University.

Among Venus’ mysteries is why it’s not even hotter than it is. Although Venus is slightly closer to the sun than Earth, it orbits more slowly and has a thicker layer of clouds trapping the heat. The planet’s atmosphere also reflects about 75 percent of the sun’s radiation. (Earth’s atmosphere reflects about 30 percent.) According to current climate models, this should make Venus even hotter than it is. “The climate on its surface is completely out of line if you extrapolated the conditions as if they were Earth,” says Fred Taylor, a planetary physicist at the University of Oxford in England. “There’s something very wrong with our modeling.”

The European Union’s hopes to launch an orbiter in a “Venus Express” mission in 2005. Esposito is urging NASA to land a robotic craft on Venus at the same time, which would be hard, since its surface is hot enough to melt lead. Any lander craft would need to be constructed of highly heat-resistant material.

“Venus is so hot that if we had the same run away Greenhouse Effect on Earth it would snuff out all life,” says Andrew Ingersoll, a planetary scientists at California Institute of Technology. “This isn’t going to happen on Earth any time soon, but the planet gives us the big picture on long term climate change.”

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Carol Lakomiak of Tomahawk, Wisconsin, was watching the sky when she noticed that, “Venus looked very strange. When viewed through my 11×70 binoculars, I saw beams of light jutting from the top and bottom of the planet, and there were moments when they were visible without optical aid.” She got her camera and took pictures of what she saw. The strange beams were captured them on film — the first-ever pictures of “Venus pillars,” which are an optical illusion formed in Earth’s atmosphere when Venus is close to the horizon, either rising or setting.

Sun pillars occur for the same reason: Miles above Earth’s surface (where it is always cold) six-sided ice crystals form in wispy cirrus clouds. Some of the crystals are flat, resembling hexagonal pancakes. They flutter downward like falling leaves. When the Sun is rising or setting, and sunlight glints off the faces of these crystals, looking like a glowing vertical beam — a “Sun pillar.”

Les Cowley, an expert in atmospheric optics, says of Lakomiak?s photos, “This is a rare sight, indeed,” he says. “I was initially surprised.” He had seen Sun and Moon pillars, but didn?t think that Venus pillars could exist. He used an optical ray tracing program called HALO to simulate the appearance of Venus setting behind distant cirrus clouds. The software, written by Cowley and colleague Michael Schroeder, is widely used to recreate images of Sun and Moon pillars and other halos. When he applied it to Venus, faint pillars emerged.

Venusdogs may exist too ? they would be the equivalent of sundogs, which are also caused by ice crystals in Earth’s atmosphere. The same flat crystals that cause pillars also create bright spots 22 degrees to the left and to the right of the Sun (and Venus). While pillars are caused by reflections from ice crystals’ wide tops, sundogs are formed by light bent or refracted from their short sides. “Sundogs can be blindingly bright — much brighter than Sun pillars,” says Cowley.

So far, no one has ever reported seeing a Venusdog. Cowley says sky watchers look for them on evenings “when sundogs or Sun pillars have been seen around the setting Sun, or when you know that cirrus clouds are near the horizon.”

To search for Venusdogs, Cowley suggests using the outstretched hand method: Hold your hand at arms length and spread your fingers. The distance between the end of your thumb and the tip of your pinky is about 20 degrees. Place your thumb over Venus and your pinky will point, more or less, to the spot where a Venusdog might be.

Photographers using timed exposures are more likely than naked-eye observers to discover a Venusdog. However, Cowley warns you should beware of internal reflections within your camera that can mimic dogs or pillars. “If you’re searching for Venusdogs,” he says, “point the camera so that Venus is also in the field of view. Shift and rotate the camera between exposures to rule out artifacts.”

Camera exposures might also reveal a faint 22-degree circular halo around the planet. Such halos are caused by hexagonal ice crystals tilted more or less randomly in all directions. “I would be delighted to see a picture of an authentic 22-degree halo around Venus,” says Cowley. Most sky watchers have only seen halos around the Sun or Moon. “The secret to observing,” he says, “is to keep looking up and be ready with a camera for the improbable. It pays off.”

To learn what?s out there in space, read ?Dark Matter, Missing Planets & New Comets? by Tom Van Flandern,click here.

To see Venuspillar photos, click here.

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