Following an important increase in the JWST financial budget, NASA has questioned the entire programme in 2005, and especially the science objectives. One of the conclusions was that JWST will not compete with the terrestrial telescopes but will keep the whole newness of its capacity.
A second was that MIRI, with its coronographic mode, will lead to the most important discoveries:
- hydrogen emission and search of the first luminous objects,
- formation of the first galaxies in the universe,
- emission of obscured elements in Active Galactic Nuclei,
- formation of stars and proto-planetary systems,
- evolution of planetary systems, sizes of Kuiper Belt objects and faint comets,
- observation of brown dwarfs and giant planets,
- search of conditions capable of supporting life.
NIRCam aims to:
- detect light from the first stars, star clusters or galaxy cores,
- study very distant galaxies seen in the process of formation,
- detect light distortion due to dark matter,
- search for supernovae in remote galaxies,
- study the stellar population in nearby galaxies, young stars in the Milky Way and the Kuiper Belt objects in our Solar System.
NIRSpec is sensitive over a wavelength range that matches the radiation from the most distant galaxies and capable of observing more than 100 objects simultaneously. The key scientific objectives of this instrument are:
- studies of star formation and chemical abundances of young distant galaxies,
- investigation of disc and gas structures in Active Galactic Nuclei (very luminous and energetic galaxies, observable at wavelengths spanning from radio waves to X-rays),
- study of the distribution of star masses in young star clusters.
MIRI (Mid-Infrared Camera-Spectrograph) combines a mid-IR camera (1.4' x 1.9') (MIRIM) and a spectrograph (R~3000) covering wavelengths 5 - 28 µm.
NIRCam (Visible/Near Infrared Camera) is a wide field (2.2' x 4.4') near-IR camera covering wavelengths 0.6 - 5 µm.
NIRSpec (Near-Infrared Multi-Object Dispersive Spectrograph) is a wide field (3.5' x 3.5') multi-object near-IR spectrometer covering wavelengths 0.6 - 5 µm at spectral resolutions of R~100, R~1000 and R~3000.
After more than 10 years of development, the JWST telescope will be launched by an Ariane 5 rocket in direction of the L2 Lagrangian point of the Earth-Sun system. This point is located at approximately 1.5 million km on the Sun-Earth axis beyond the Earth orbit in the opposite direction to the Sun. This point is in the shadow cone of the Earth, but JWST will orbit around this point at great distances (several hundred thousand kilometres around), which implies it will be illuminated and heated by the Sun.
After launch, JWST will undergo a commissioning period of about 6 months during which all on-board sub-systems and scientific experiments and all ground means will be tested before declaring the telescope operational.
The operational phase is planned to last 5 years. As for the Hubble Space Telescope, the Flight Dynamics Facility will be located at the NASA Goddard Space Flight Center while the Science Operation Center will be hosted at the Space Telescope Science Institute. One expertise centre in Europe for MIRI and one in France for MIRIM will participate to the performance improvements during the whole mission.