How do planets form?

Can you explain the current understanding of how planets form?
When gas collapses to form a star, a portion of the gas forms into a disc. As the disc cools, some of the iron, silicon, carbon, oxygen and water condenses to form grains. When grains collide, they can stick and grow into pebbles. We’re still unsure of the details, but somehow the pebbles become incorporated into larger bodies that grow to become asteroids, rocky planets and the cores of giant planets.  

How has the discovery of exoplanets changed our theories of planetary formation?
The discovery of exoplanets very different to our own has opened our mind to the diversity of planetary systems that nature can produce. The observations have inspired a wide range of theories about how planets of various masses and sizes could be arranged into the configurations that we observe today.  

Could our understanding of how the planets formed in the Solar System be wrong?
NASA’s Kepler mission has demonstrated that most planetary systems are unlike our Solar System. Instead of designing planet formation to reproduce our Solar System, now we must develop theories that make a wide variety of planetary systems and only occasionally produce something similar to our system.  

What future observations are needed to better understand planetary formation?
We’ll need lots more observations. Fortunately, there are several new facilities in the works that will lead to major advances in our ability to directly image large planets far away from their star and to resolve structures in the protoplanetary discs.Hopefully, the major space agencies can co-operate to develop at least two more generations of major space-based observatories, so we’ll be able to discover and characterise Earth-like planets.