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The Question

(Submitted January 06, 1997)

What would happen to the Earth if the Sun was by Pluto?

The Answer

We will assume for the sake of argument that you mean if the Sun were farther away, say at the distance of Pluto, which is about 40 times farther away from the Earth as the Sun is. At such a distance, the Sun would appear as little more than the brightest star in the sky, similar in size and brightness to the way Venus looks in our night sky.

The big difference (apart from needing lamps to read by all day) is the fact that since the Sun would be 40 times farther away, the Earth would receive MUCH less energy, which drops off as the square of the distance. This is called an inverse-square law. An object twice as far away from the Sun receives only 1/(2*2)=1/4 as much energy. For an object 40 times farther away, the energy is 1/(40*40)=1/1600. This reduced energy would have severe effects on Earth. It would lead to a drastic cooling in the atmosphere, lowering the temperature down to about -228 to -238 C. (Water freezes at 0 C.) At this new temperature, all the nitrogen in our atmosphere would turn into a liquid, while all the water would be solid.

Since the Earth is naturally radioactive, it has a good store of energy which would still be released, mostly through the radioactive decay of Uranium. This heat might lead to the development of vents on the frigid surface.

This could possibly lead to the development of life at the vents on the ocean floor where the ice in the oceans would be melted into water. Life as we know it on the surface of the planet would not be possible. (We got some information for this answer from the web pages at the University of Arizona: http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html)

Cheers,
Mike Arida and Padi Boyd
for Imagine the Universe!

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