July 9, 2010
from YouTube Website
fires of a sun's birth... twin planets emerged. Then their paths
diverged. Nature draped one world in the greens and blues of life.
While enveloping the other in acid clouds... high heat... and
volcanic flows. Why did Venus take such a disastrous turn?
The count is approaching 500... and rising. These alien
worlds run the gamut... from great gas giants many times the size of
our Jupiter... to rocky, charred remnants that burned when their
parent star exploded.
Amid these hostile realms, a few bear tantalizing hints of water or ice... ingredients needed to nurture life as we know it.
The race to find other Earths has raised anew the ancient question...
With so little direct evidence of these other worlds to go on, we have only the stories of planets within our own solar system to gauge the chances of finding another Earth. Consider, for example, a world that has long had the look and feel of a life-bearing planet.
Except for the moon, there's no brighter light in our night skies
than the planet Venus... known as both the morning and the evening
But how Earth-like is it? The Russian scientist Mikkhail Lomonosov caught a tantalizing hint in 1761. As Venus passed in front of the Sun, he witnessed a hair thin luminescence on its edge.
Venus, he found, has an atmosphere. Later observations revealed a thick layer of clouds.
Astronomers imagined they were made of water vapor, like those on Earth.
NASA sent Mariner 2 to Venus in 1962... in the first-ever close planetary encounter. Its instruments showed that Venus is nothing at all like Earth.
Rather, it's extremely hot, with an atmosphere made
up mostly of carbon dioxide.
On our planet, the only naturally
occurring source is in the high-temperature, high-pressure
environments of undersea volcanoes. It comes in handy for extracting
caffeine from coffee beans... or drycleaning our clothes.
landers sent back pictures showing that Venus is a vast garden of
rock, with no water in sight. In fact, if you were to smooth out the
surface of Venus, all the water in the atmosphere would be just 3
centimeters deep. Compare that to Earth... where the oceans would
form a layer 3 kilometers deep.
The winds are light, only a
few miles per hour... but the air is so thick that a breeze would
knock you over. Look up and you'd see fast-moving clouds...
streaking around the planet at 300 kilometers per hour. These clouds
form a dense high-altitude layer, from 45 to 66 kilometers above the