Hydrogen is the most abundant element in the universe, and it often combines with itself to form molecular hydrogen (H2).

Ion-molecule reactions are the primary mechanism by which molecules form in space. These reactions involve the transfer of charge between ions and molecules, leading to the formation of new chemical bonds.

Polycyclic aromatic hydrocarbons (PAHs) are responsible for the blue-green color of reflection nebulae. These molecules absorb ultraviolet light from nearby stars and re-emit it as visible light, producing the characteristic color.

Aeronomy is the study of chemical reactions and processes that occur in the atmospheres of planets, including giant planets.

Ammonia (NH3) is commonly found in the atmospheres of cool, dense interstellar clouds. It is formed through ion-molecule reactions involving nitrogen and hydrogen.

Photodissociation is the process by which molecules are broken apart by high-energy radiation, such as ultraviolet light, in space.

Hydrogen (H2) is responsible for the characteristic red color of emission nebulae. When hydrogen atoms are excited by high-energy radiation, they emit red light as they return to their ground state.

Surface chemistry is the study of chemical reactions and processes that occur on the surfaces of planets and moons.

Methane (CH4) is commonly found in the atmospheres of hot, young stars. It is formed through reactions involving carbon and hydrogen.

Recombination is the process by which molecules are formed through the combination of atoms or ions.

Oxygen (O) is responsible for the characteristic green color of auroras. When oxygen atoms are excited by high-energy particles, they emit green light as they return to their ground state.

Interstellar chemistry is the study of chemical reactions and processes that occur in the interstellar medium, the vast space between stars.

Nitrogen (N2) is commonly found in the atmospheres of Earth-like planets. It is formed through reactions involving nitrogen and hydrogen.

Dissociation is the process by which molecules are broken apart by collisions with other particles.

Sulfur (S) is responsible for the characteristic yellow-orange color of supernova remnants. When sulfur atoms are excited by high-energy radiation, they emit yellow-orange light as they return to their ground state.