The bright gibbous Moon has a bright companion tonight -- the planet Saturn. It looks like a golden star, a little to the upper left of the Moon at nightfall.
We see Saturn and the Moon not because they produce light, but because they reflect sunlight. But both worlds do emit energy of their own -- the "heat" energy known as infrared. The Moon absorbs some of the Sun's visible light, then re-radiates it back into space as heat.
Saturn does the same thing. But the planet actually produces more energy than it gets from the Sun.
Part of that energy comes from Saturn's great bulk. Because the planet is so massive, it has a strong gravitational pull. That squeezes Saturn's interior, heating it to tens of thousands of degrees. Some of that heat works its way through the surrounding layers of hydrogen and helium gas and radiates away into space.
But Saturn's gravity can't account for all of the planet's infrared energy.
The rest may come from a "rain" of helium onto the planet's solid core. As the helium plunges thousands of miles toward the core, it picks up a lot of speed. When it hits the core, the energy of its motion is converted to heat, which is then carried out into space.
The helium "rain" hasn't been confirmed. But so far, it's the leading idea for explaining Saturn's extra glow.
Again, look for Saturn leading the Moon across the sky tonight. They're high in the sky at nightfall, and set a couple of hours before sunrise.
Script by Damond Benningfield, Copyright 2009
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