Webb's mission builds upon and expands the work of NASA's Great Observatories, four remarkable space telescopes whose instruments cover the waterfront of electromagnetic spectra. The four overlapping missions enabled scientists to observe the same astronomical objects in the visible, gamma ray, X-ray and infrared spectra.
The school-bus-sized Hubble, which sees primarily in the visible spectrum with some ultraviolet and near-infrared coverage, kicked off the program in 1990 and, with further servicing, should last long enough to hand off the baton to Webb. Appropriately named for Edwin Hubble, the astronomer who discovered many of the occurrences that it was built to investigate, the telescope has since become one of the most productive instruments in scientific history, bringing phenomena like star birth and death, galactic evolution and black holes from theory to observed fact [source: NASA].
Joining the Hubble in the big four are the Compton Gamma Ray Observatory (CGRO), Chandra X-ray Observatory and Spitzer Space Telescope.
- The CGRO, launched in 1991 and no longer in service, detected high-energy, violent spectacles in the 30 kiloelectron volts (keV) to 30 gigaelectron volts (GeV) spectrum, including the energy-spewing nuclei of active galaxies.
- Chandra, deployed in 1999 and still going strong, monitors black holes, quasars and high-temperature gases in the X-ray spectrum, and offers vital data about the universe's birth, growth and ultimate fate.
- Spitzer, which occupies an Earth-trailing orbit, views the sky in thermal infrared (3-180 microns), a bandwidth useful for viewing star births, galactic centers and cool, dim stars, and for detecting molecules in space.
Webb will gaze deeply into the near- and mid-infrared, aided by its position at the L2 point beyond the moon and by its solar shields, which will block intrusive light from the sun, Earth and moon while also efficiently cooling the craft. Scientists hope to observe the very first stars in the universe, the formation and collision of infant galaxies, and the birth of stars and protoplanetary systems -- possibly ones containing the chemical constituents of life.
These first stars could hold the key to understanding the structure of the universe. Theoretically, where and how they formed relates to early patterns of dark matter -- unseen, mysterious matter detectable by the gravity it exerts -- and their life cycles and deaths caused feedbacks that affected the formation of the first galaxies [source: Bromm et al.]. And as supermassive, short-lived stars, estimated at around 30-300 times the mass (and millions of times the brightness) of our sun, these firstborn stars might well have exploded as supernovae then collapsed to form black holes, later swelling and merging into the huge black holes that occupy the centers of most massive galaxies.
Witnessing any of this is a feat beyond any instrument we've built so far. That's about to change, thanks to a package of instruments -- and a spaceship -- built for the job.