Question

How is the size of a planet related to the thickness of its atmosphere? explain.

Answer 1

The amount of gravitational pull helps determine the gases that can form an atmosphere around a large body in space. So the mass of an object also determines the density of these gases. Note that several factors come into effect for a large object to sustain their gases if present.

Answer 2

Mainly, the mass of a planet doesn't matter, considering many planets are made up of gas, and how in different situations, atmospheres can be destroyed (The Sun burnt off Mercury's Atmosphere). However, in some cases, the planet can be in a good situation on the galaxic map, and have great conditions for an atmosphere, such as Earth. In which case, the mass of an object can attract a smaller object, causing gravity. Therefore, the bigger the mass of a planet when in right and specific conditions, the more atmosphere it can attract, if there is any floating by the planet.
If it is bigger it will have more gravitational influence and therefore gather more gases