The first planet outside our solar system was discovered in 1992. Since then, we have discovered a multitude of planets around other stars. We have come to the realization that planets are in fact quite common. Most of the planets discovered so far are large gas giants like Jupiter, although that may be because larger planets are more easily detected. Recent discoveries have included smaller planets, from those a few times more massive than Earth (known as Super Earths) to those Earth-size and smaller. The ultimate objective of the search is to find planets orbiting in the habitable zone of their star, where it is possible for liquid water and perhaps even life to exist.
To trace the origins of the Earth and life in the Universe, scientists need to study planet formation and evolution, including the material around stars where planets form. A key issue is to understand how the building blocks of planets are assembled. Scientists do not know if all planets in a planetary system form in place or travel inwards after forming in the outer reaches of the system. It is also not known how planets reach their ultimate orbits, or how large planets affect the smaller ones in solar systems like our own.
The icy bodies and dust in the outer reaches of our Solar System are evidence of conditions when our Solar System was very young. Scientists can directly compare those conditions to the objects and dust observed around other stars. The sensitive instruments on the James Webb Space Telescope will be able to obtain infrared images of giant planets and planetary systems and characterize their ages and masses by measuring their spectra. Webb will also be able to measure spectra of the disks around other stars to determine the constituents of such disks that give rise to planetary systems.
In addition to studying planets outside our solar system, scientists want to learn more about our own home. Studying the chemical and physical history of the small and large bodies that came together to form the Earth may help us discover how life developed on Earth. Webb will be powerful enough to identify and characterize comets and other icy bodies in the outermost reaches of our solar system, which might contain clues to our origins on Earth.
Image credits: image of HR8799 and its planets - NRC-HIA, Christian Marois, and the W.M. Keck Observatory, Methane Absorption by the Atmosphere of Extrasolar Planet 189733b, detected by the Hubble Space Telescope - NASA, ESA, and A. Feild (STScI)
Want to know more? Visit the James Webb Space Telescope project home page.