The Solar System condensed from a cloud of molecules and dust, similar to the clouds of interstellar dust and gas observed in our Galaxy today. Discoveries over the past ten years are revealing many similarities between dust elsewhere in the Galaxy and the composition of comets.

"When we look at dust and gas in the interstellar medium, we see molecules that are found on comets and on Earth. They are important components for building up more complex molecules," says Pascale Ehrenfreund, an astrochemist from the Leiden Observatory in the Netherlands and a co-investigator on ESA's Infrared Space Observatory (ISO). Of the 120 molecules so far detected in interstellar gas, about half are organic. "The largest has 13 atoms (HC₁₁N), but we think there are much larger molecules out there," says Ehrenfreund.

ISO helped detect many of these molecules. Most notable was its finding that water is just about everywhere in space. In 2007, ESA's far infrared and submillimetre mission the Herschel Space Observatory, will continue to unravel the complexities of interstellar chemistry and further our understanding of star formation.

"We know that our Sun formed in a similar way to other stars which are forming in front of our eyes (or at least our telescopes) today," says Göran Pilbratt, ESA's project scientist for Herschel. "What we don't know is to what extent planets form with these stars - and the nature of these planets. This is a problem that must be addressed by looking for and studying planets around already-formed stars, and by trying to understand the process of star formation itself, which is one of the areas where Herschel is expected to have a large impact."