1. Introducing space chemistry

Most of the matter in the universe is found in galaxies, which contain large numbers of stars. It is these stars that illuminate our night sky with a thousand lights. However, there is also a vast amount of cold matter in space, invisible to the naked eye. In fact, the immense expanses that separate the stars are not empty, as has long been thought. In fact, they are filled with a mixture of gas, dust and energetic particles, making up what is known as the interstellar medium, which accounts for 10% of the total mass of matter in a galaxy. This medium, condensed into regions called "clouds" in which gas and dust are concentrated, is in constant interaction with the stars that are born, live and die there.

Using different regions of the electromagnetic spectrum, astronomers have measured the composition of gas and, in part, dust. In so-called diffuse clouds, with...