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When Comets Crack

7 Oct 2013, 12:59 UTC
When Comets Crack
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As Comet ISON nears the Sun, the big question is whether it will remain intact or shatter into pieces. Since comets are mostly made up of ice, it’s reasonable to suspect that the heat of the Sun causes them to disintegrate. But that’s not the whole story. To discover why comets fall apart, we need to look at the force currently keeping your feet firmly on the ground — gravity.

Gravity is the weakest of the four physical forces. We can really only see its effects when some massive body is involved, so the best examples of gravity are usually astronomy-related. Despite its relative weakness, gravity is responsible for some pretty profound things: our spherical Earth, its ever-changing oceans, and for keeping all the planets in the solar system orbiting around the Sun.

Earth’s tides are one way we all commonly experience gravity. The shoreline at the beach comes in for high tide and goes out at low tide because of the Sun-Earth-Moon system. Our Moon is big and close enough that it gravitationally attracts the oceans, causing a bulge on opposite sides of the Earth. The solid Earth spins underneath this bulge every day, causing the calm, (in most ...

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