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Moon and Venus

September 9, 2012

The Moon closes in on Venus, the “morning star,” the next few days. It’s a good distance away from Venus tomorrow, but will stand side by side with the planet on Wednesday.

Venus’s surface is hidden from view by clouds that cover the entire planet. In fact, they’re one reason that Venus looks so bright.

In decades past, many scientists thought the clouds were hiding a steamy world covered with vast oceans of water. It turns out, though, that Venus is far too hot for water — surface temperatures average more than 850 degrees Fahrenheit.

Yet Venus may have been covered with water early in its history — perhaps more water than on present-day Earth. Observations by orbiting spacecraft suggest that Venus lost its water through interactions with the Sun.

Solar radiation split apart water molecules in the atmosphere. The lightweight hydrogen atoms escaped into space, while the heavier oxygen atoms combined with rocks at the surface. More water then evaporated into the atmosphere, where it, too, was destroyed by sunlight.

That process left less water to bind with carbon dioxide to form rocks, so the ratio of carbon dioxide in the air went up. CO2 traps heat, so it caused Venus’s surface to get ever hotter. Over time, this cycle destroyed the Venusian oceans, leaving the planet hot and dry — just as it is today.

Look for Venus far below the Moon at first light tomorrow, a little closer on Tuesday, and standing next to it on Wednesday.


Script by Damond Benningfield, Copyright 2012

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