Little did astronomers know that these tiny specks of dust are responsible for the very existence of the universe as we see it now. It might not seem so for someone living on Earth, but the most abundant element in the universe is hydrogen. This is the stuff stars are made of. The hydrogen atom is the lightest and simplest atom you can think of. Put two hydrogen atoms together and you have the lightest, most abundant, and simplest molecule.
Molecular hydrogen has two main roles in interstellar space.
First, it helps the formation of stars by carrying away some of the heat that is produced when gas rushes towards the core of a future star. Second, molecular hydrogen helps form other, more complex molecules. Just about thirty years ago, in a series of landmark papers, Edwin Salpeter and his student David Hollenbach of Cornell University proposed a model. It was known that molecular hydrogen doesn't form by a chance encounter of two hydrogen atoms in the nearly empty space between stars, but a surface is required to make a chemical reaction happen. Another hydrogen atom might land on this grain before the first atom has a chance to evaporate.