JWST will address a number of key topics in modern astronomy providing astronomers with the tools needed to understand the formation of galaxies, stars, planets, and ultimately life.
The primary science goals guiding the design of JWST can be grouped into four broad themes:
The End of the Dark Ages: First Light and Reionisation seeks to identify the first stars and galaxies, and to look at when and how reionization occured.
Assembly of Galaxies examines how the first galaxies formed and evolved, probes the formation and redistribution of heavy elements, and looks at the role of black holes in galaxy evolution.
The Birth of Stars and Protoplanetary Systems focuses on the birth and early development of stars and the formation of planets.
Planetary Systems and the Origins of Life studies the physical and chemical properties of planetary systems (including our own) and investigates the potential for life elsewhere in the Universe.
The observations required to address these science themes require a large telescope sensitive to the infrared Universe.
The JWST observatory consists of a passively cooled, 6.5-m aperture telescope, optimised for diffraction-limited performance in the near-infrared (2 - 5 μm) region, but with extensions to either side into the visible (0.6 - 2 μm) and mid- infrared (5 - 28 μm.).
The large aperture and shift to the infrared embodied by JWST is first and foremost driven scientifically by the desire to follow the contents of the faint extragalactic Universe back in time and redshift to the epoch of 'First Light' and the ignition of the very first stars. Nonetheless, like its predecessor, JWST will be a general-purpose observatory and carry a suite of astronomical instruments capable of addressing a very broad spectrum of outstanding problems in galactic and extragalactic astronomy. In contrast to HST, however, JWST will be placed into a Sun-Earth L2 halo orbit and will not be serviceable after launch.