As you sink below the surface of the ocean, the pressure builds in a hurry. At a depth of about 650 feet, it's 20 times greater than the air pressure at the surface -- strong enough to crush the hull of a World War II submarine. Double that depth, and you've reached a reasonable operating depth for a modern submarine. Double it again, and almost any sub is a goner.
Yet the pressure at the surface of the planet Venus is even greater. It's equivalent to an ocean depth of about 3,000 feet, where the pressure is two-thirds of a ton per square inch.
Not surprisingly, Venus is a hard place to explore. The Soviet Union dropped several probes on the planet's surface, but none of them survived for more than about an hour.
Getting people to the surface would require a monumental feat of engineering. A lander most likely would have to resemble a bathysphere -- a hollow metal ball that carries people into the ocean depths. Yet thick metal walls are heavy, so it would take a lot of rocket power to launch such a craft from Earth.
Instead, a Venus expedition might have to wait until we begin mining the asteroids. A craft could be built out in space, and sent from there to plunge into the atmosphere of Venus -- an atmosphere that's more than a match for today's technology.
Look for Venus low in the west just after sunset. It's the brilliant "evening star." And it has a bright companion: the planet Mercury, which is just a bit to its right.
Script by Damond Benningfield, Copyright 2010