Could a gas go directly to a solid without becoming a liquid?
Changing a substance from its physical state of a gas to the physical state of a solid requires the removal of thermal energy. A gas has particles that have larger amount of kinetic or moving energy, they are vibrating very rapidly. A solid has particles with lower amounts of kinetic energy and they are vibrating slower without changing position. This change of state from a gas to a solid is not a very common phase change but is referred to as deposition. It is called deposition because the particles in the gas form are depositing into a solid form.
Examples of Gas to Solid:
Making dry ice or solid carbon dioxide involves the removal of gaseous carbon dioxide from air and using cold temperatures and higher pressure causes the gas particles to skip the liquid phase and deposit into a solid to form a chunk of dry ice.
A carbon dioxide fire extinguisher has been filled with gaseous carbon dioxide but inside the canister the higher pressure causes this to turn into solid carbon dioxide which later is released as a white powder when putting out a fire.
In severely cold temperatures frost will form on windows because the water vapor in the air comes into contact with a window and immediately forms ice without ever forming liquid water.
Deposition has become a manufacturing technology application where solid alloys are heated to a gaseous state and then sprayed onto things like semiconductors. When the spray is released onto the semiconductor the heat energy is lost and the gaseous substance becomes a solid metal alloy.
Yes. The Phase Diagram of a substance shows when that substance is in which state. Here is a phase diagram of water (source):
You can see that there are phase boundaries between each pair of states. Where all three states meet is the Triple Point. The boundary where solid and gas (vapor) are adjacent is generally below the triple point in both temperature and pressure; for water it starts at the familiar freezing temperature, but at less than 1% of standard atmospheric pressure. If you want to get water to desublimate, you'll have to do it in near-vacuum.
It's called deposition. It occurs fairly frequently with water vapor, resulting in snow (rather than hail which usually results from freezing liquid water) or frost.