Venus: Earth's troubled sister
The planet Venus is one of the most familiar sights in the night sky, shining in the west at sunset, or brightening up the early morning gloom. Venus is always close to the sun in the sky, the reason being that Venus is actually closer to the sun than the Earth. Since Venus's path can never take it outside the Earth's orbit, we never see Venus on the opposite side of the sky from the sun. Hence, the lovely planet becomes both the morning and evening star, depending on which side of the sun itís on at a given time.Skip to next paragraph
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Venus has a special draw on our imaginations, and not just because if its lovely glow or association with the goddess of love. Venus is the closest planet to Earth, in more than one way. Literally, Venus is the planet that comes closest to Earth in its orbit. As we swing by Venus in a close approach between our two orbits, Venus seems to become impossibly bright, and UFO sightings increase significantly.
But Venus is also the twin sister to Earth in our solar system. Venus' orbit is actually quite similar to the Earth, with Venus orbiting only 20 percent closer to the sun than we do. Venus is also almost the same size and mass as our planet, and has the most similar chemical composition. But looking toward Venus in the sky, I tend not to feel a warm camaraderie between our two worlds. On the contrary, Venus actually makes a lot of scientists distinctly uneasy.
At first, Venus was merely mysterious. From Earth-based telescopes, all we could really discover about the planet was that it was cloudy. High, pale-colored clouds blanket the entire surface. At first the clouds seemed encouraging; planetary scientists of a hundred years ago imagined oceans and forests fed by eternal rains. Perhaps Venus could support life; perhaps Venus was much like Earth. But when we were finally able to send probes to our sister planet, we got a huge shock.
As serene and lovely as Venus seems, in reality the planet is as about as close to the traditional version of hell as our imaginations allow. Underneath the clouds, Venus is the hottest planet in our solar system, with average temperatures around 900 degrees Fahrenheit. Interestingly, Venus is far hotter even than the planet Mercury, which is twice as close to the sun as Venus is. And if the heat wasn't enough, the atmospheric pressure is enormous (90 times that of sea level on Earth), strong enough to crush a spaceship like an empty soda can. The landscape is pockmarked by faults, scars, and evidence of giant magma bubbles, which rose and fell back into Venus' crust, leaving behind features resembling thousand-mile wide collapsed souffles. Venus is, of course, far too hot for liquid water to exist, but that doesn't stop it from raining it's just that the rain is made of highly corrosive sulfuric acid.
These extreme conditions make Venus an extremely difficult place to explore. The atmosphere is completely filled with clouds made of sulfuric acid aerosols that never break open to reveal the surface. It wasn't until we were able to fly satellites to orbit Venus and bounce radar down through the clouds that we had any idea what the surface looked like at all. The Soviet Union managed to land two spacecraft on Venus in the late 1970s, both of which hurriedly transmitted a picture or two before succumbing to the brutal conditions. The view: a hot, bleak desert with acid rain falling from an orange-colored sky.
Even putting our Earth-centric notions aside, something seems to have gone terribly wrong with Venus. Why are the conditions on the planet so extreme and inhospitable? It's not as simple as Venus being closer to the sun. A 20 percent difference in distance might explain a temperature difference of a few tens of degrees, but hardly over 800 degrees! The answer lies in a phenomenon that's received plenty of media attention on Earth in the last few years: the greenhouse effect. Simply put, the greenhouse effect is the ability of an atmosphere to retain heat. Taken in moderation, the greenhouse effect is actually quite a benign thing. Our own planet, in fact, would not be the lovely warm place we know today without it. The Earth is actually far enough from the sun that without the greenhouse effect, the average temperature on our planet would be well below freezing, and we would be locked in a permanent Ice Age.