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

The bigger the planet the bigger the gravitational pull of the planet , which is also stipulated in Newton Law of gravity. The bigger the planet, therefore, the bigger the atmosphere it would have. This is because its gravity is able to overcome the kinetic energy of the gas molecules (especially when heated by rays from a star they are orbiting) that would allow the gas atoms/molecules to escape into space. This is also why the large planets are all gas giants such as Jupiter.

straight probes are used primarily for measuring flow as it is approaching the test area. its geometry allows the probe to be mounted so that it is in the direct line of airflow.

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.