Astrochemistry, the overlap of the disciplines of astronomy and chemistry, is the study of the abundance and reactions of chemical elements and molecules in space, and their interaction with radiation. The word astrochemistry can refer to both the Solar System, and the interstellar medium. The study of the abundance elements and isotope ratios in Solar System objects (such as meteorites), is also called cosmochemistry, and the study of interstellar atoms and molecules and their interaction with radiation is sometimes also called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds, is of special interest because it is from these clouds that solar systems form.