Construction-site inspection

摘要

How do you build a planetary system? Astronomers are tackling the question by peering back in time at the gas and dust surrounding stars younger than our Sun. A laboratory experiment in planetary formation would take perhaps a hundred million years tocomplete. Luckily, nature has been kind in providing some local analogues of the early nebula that formed our Solar System. These flattened structures of gas and dust around other stars are called circumstellar disks, and to look at disks ranging from amillion years old up to the age of the Sun is to look at the planetary construction process. The challenge for astronomers is to make measurements in enough detail to allow comparisons with a Solar System whose present form we know well. Three papers, one in this issue, now provide new examples of how astronomers are facing up to that challenge.