Geological TOS Review: Episode #4 - "The Naked Time"

In the episode "The Naked Time," the Enterprise is orbiting Psi 2000 to observe the disintegration of the planet. The doomed world is completely covered in ice and snow. 

"An ancient world, now a frozen wasteland, about to rip apart in its death throes. Our mission, pick up a scientific party below, observe the disintegration of the planet."

Later in the episode Mister Spock mentions that the star in the Psi 2000 system went dark, explaining the low temperatures on the planet. 

“Obviously, this planet is condensing more rapidly than expected. A valuable study. We may be seeing Earth's distant future. Before its sun went dark, this planet was remarkably similar to yours.”

It is unlikely that Earth will end as completely frozen world. When the Sun will become a Red Giant in estimated five billion years, temperatures will significantly rise and Earth will eventually be engulfed and destroyed by the expanding Sun. However, geological evidence suggests that almost 650 million years ago our planet temporarily became a "Snowball Earth." How this happened is unknown, but the release of gases by volcanoes probably saved the planet and its first terrestrial life forms, as the planet warmed due the greenhouse effect of the carbon dioxide gas. It is curious to note that chief medical officer McCoy discovers unknown organic molecules in the ice of Psi 2000.

In the episode it is never exactly explained how the planet is supposed to disintegrate. In the episode changes in the mass and also gravitational and magnetic field of the planet play an important role, as the Enterprise can't leave orbit due the interferences.  Disturbances of the gravitational field by a bypassing, large planet could cause the break up of a celestial body. In our solar system, the ring systems of the large gas giants may are the remains of a disintegrated moon, torn apart as it went to close to the planet. Also planets in other star systems can be doomed. Orbits of planets in binary systems are unstable thanks to the Kozai-effect. The gravitational force of one of the two stars in the system will pull the planet out of its orbit. As the planet's orbit collapses, it will go to close to the host star and torn apart by its gravitational force.