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Mars, as it turns out, once had a propensity for juggling its polar ice caps from one end of the planet to the other.
A perennial wobble in Mars' tilt pushed one pole closer to the sun, causing water ice to evaporate and refreeze at the colder pole, new research shows. Every 51,000 Martian years, the wobble would bring the colder pole closer to the sun again and shuffle the ice cap back to the opposite pole.
Escape of an Atmosphere
The thickness of a planet's atmosphere depends on the planet's gravity and the temperature of the atmosphere. A planet with weaker gravity does not have as strong a hold on the molecules that make up its atmosphere as a planet with stronger gravity. The gas molecules will be more likely to escape the planet's gravity. If the atmosphere is cool enough, then the gas molecules will not be moving fast enough to escape the planet's gravity. But how strong is ``strong enough'' and how cool is ``cool enough'' to hold onto an atmosphere? To answer that you need to consider a planet's escape velocity and how the molecule speeds depend on the temperature.