John E. Chambers
Planetary formation theory; planetary dynamics; extrasolar planets
B.A., Physics, University College, Oxford University, 1990 Ph.D., Astronomy, Manchester University, 1994
How planets form and why they appear the way they do are two long standing puzzles. Solving these puzzles is made more challenging by the fact that planet formation elsewhere in the universe is largely unobservable using existing telescopes. Astrophysicist John Chambers approaches this problem from a different direction using computer simulations to model the formation of planetary systems and to calculate the properties of the planets that form. His ultimate goals are to determine what forces shape the physical and chemical properties of planets, and to estimate how common Earth-like planets capable of supporting life may be.
It is generally believed that the Sun's planets formed by collisions and mergers between many small bodies called planetesimals. In the outer Solar System, far from the Sun, these planetesimals would have been composed of a mixture of many materials including water and other volatile compounds essential to life. Closer to the Sun, in the region now occupied by Earth, temperatures were too high for volatile materials to condense. Planetesimals here were largely composed of dry rock and metal. Chambers uses his numerical models of planet formation to assess how likely it is that volatile rich material from the outer Solar System would have been transported to Earth while it was still growing, enabling the formation of the planet's atmosphere and oceans. This work is also being extended to other planetary systems to help assess the likely compositions of newly discovered extrasolar planets.
The outer Solar System is dominated by four giant planets that are tens to hundreds of times more massive than Earth. These giants are largely composed of gases such as hydrogen and helium. It is likely that these planets were once smaller, solid bodies like the terrestrial planets. However, the Sun's outer planets grew large enough for their gravity to capture large amounts of gas from the cloud of gas surrounding the young Sun. Chambers is using simulations of planet formation to find out why planets in the outer Solar System grew larger than those closer to the Sun, and how they were able to grow fast enough to accrete large amounts of gas before the Sun's gas-rich cloud dispersed.
One of the great surprises from the discovery of extrasolar planets is that planetary systems are highly diverse, and many look very different from the Solar System. In particular, many systems contain several planets a few times more massive than Earth in tightly packed orbits that are closer to their star than Mercury is to the Sun. This suggests that the clouds of material surrounding other stars when they were young were either very different from the Sun's initially or they evolved in a different way. Chambers is using his numerical models of planet formation to determine whether similar starting situations can evolve along different paths, allowing the formation of a variety of planetary systems. This work will also shed light on why so many other systems look different from our own, and what special circumstances may have led to the formation of the Solar System.