John Chambers is one of the world leaders in the dynamics of terrestrial planet formation. Prior to his Carnegie appointment, he was a research scientist at the Search for Extraterrestrial Intelligence Institute in Mountain View, California.

With the proliferation of extrasolar planet discoveries, the race is on to find habitable worlds akin to the Earth. At present, however, extrasolar planets less massive than Saturn cannot be reliably detected. Astrophysicist John Chambers models the dynamics of these newly found giant planetary systems to understand their formation history and to determine the best way to predict the existence and frequency of smaller Earth-like worlds. As part of this research he explores the basic physical, chemical, and dynamical aspects that led to the formation of our own solar system—an event that is still poorly understood. His ultimate goal is to determine if similar processes could be at work in the newly discovered planetary systems, which could then help predict smaller, extrasolar bodies that might harbor life.

It is generally believed that the Earth and other terrestrial planets formed by the accretion of many rocky planetesimals. Water and other life-giving volatile materials are thought to have originally accreted in planetesimals located beyond 1 astronomical unit (AU) from the Sun in the early solar nebula (1 AU = distance from the Earth to the Sun). These small bodies were subsequently driven toward the inner solar system by the gravitational perturbations from Jupiter and Saturn. Chambers’s models consider both observed and hypothetical planetary systems. He and colleagues recently calculated that the evolution of the terrestrial planets and the asteroid belt was heavily dependent on the orbital characteristics of the giant planets. He further demonstrated that the amount of volatiles present was affected by the timing of giant-planet formation.

These simulations show types of terrestrial planets that form in giant-planet systems. Only terrestrial planets are indicated. Earth- ike planets can form at different distances in different systems. The colors indicate the fraction of the planet’s mass consisting of water, going from gray (no water), through red, yellow, green, light blue, dark blue, and white. Each progressive color implies 5 times more water. Earth (top line) is yellow, with relatively little water. (The scale is astronomical units — the Earth-Sun distance.)

Based on evidence of the rate of impact cratering on the Moon, Chambers recently proposed a bold hypothesis about our early solar system: five planets instead of four originally accreted inside the asteroid belt. He believes that the missing fifth planet was in an unstable orbit between Mars and the asteroid belt and was ejected by 600 million years of gravitational perturbations induced by the other planets. He proposes that the missing planet’s exodus disrupted asteroid fields, creating an increase in lunar impacts.

Chambers devises innovative numerical simulations in his work. Some of his calculations are based on a scheme used by Carnegie’s George Wetherill, who pio-neered studies in planetary accretion. In 1999 Chambers combined two integration algorithms to develop a new mathematical technique he named Mercury. This tech-nique is able to simulate planetary and asteroid accretion faster and more accurately than previous methods and is now used by different research groups worldwide.