Where and how do planetary systems form and evolve?
After a star is born, leftover gas and dust swirl around the young star, forming a circumstellar disc of gas and dust. The grains of dust in this disc are the seeds of future planets. Once most of the dust has collapsed together to form the planets, the disc disappears, leaving behind only a thin ring of debris. Astronomers have indirectly detected a number of planetary systems outside our own. Although the planets themselves are difficult to image directly, observations in the infrared will help understand how these planetary systems formed and evolved. Herschel’s instruments will analyse the chemistry at work in the circumstellar material and possibly even look for chemical traces of life. Both protoplanetary discs and debris rings are favourite targets for infrared space telescopes. Many have been studied in particular by Spitzer, and Herschel will extend this into new regimes ISO and Spitzer have shown that the formation of planets around stars must be a common event. According to
