Moon and Venus
When it comes to making a planet comfortable for life, it's all about location. Consider Earth and Venus. The planets were born at the same time, from the same raw materials, so they probably started with roughly equal amounts of water. Yet today Earth is cozy and wet, while Venus is hot enough to melt lead and almost completely bereft of water.
The main difference, of course, is location.
On average, Venus is about 25 million miles closer to the Sun than Earth is. All that extra heat turned Venus's liquid water to steam, which rose high into the atmosphere.
Far above the surface, solar energy split the water molecules apart. A steady "wind" of particles from the Sun then blew the hydrogen and oxygen atoms out into space.
Since Earth was farther from the Sun, it got less heat. And our planet was protected by a strong magnetic field, which deflected the solar wind and kept most of the hydrogen and oxygen locked in the atmosphere. So today, Earth is a comfortable abode for life, while Venus is a desolate furnace with nary a drop of water.
Even though you wouldn't want to visit Venus, it's still fun to look at. The brilliant "morning star" rises about 90 minutes before the Sun. Tomorrow, it's just to the lower left of the Moon at first light. In fact, after sunrise, the Moon will actually cover the planet for a while. Even though it takes place during daylight from most of the U.S., it's visible if you know where to look. Binoculars provide the best view.
Script by Damond Benningfield, Copyright 2009
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