Humans have long been fascinated with the sky . Our earliest stories speak of heroes laid to rest amidst the stars. Ancient structures such as Stonehenge were constructed to mark the apparent motions of the sun. Galileo in 1609 pointed an early telescope at Saturn's rings and Jupiter's moons, sparking a cultural revolution that toppled superstitions and re-directed humankind toward enlightened humanism based on experience.
A new era in astronomy, and perhaps in scientific history, begins (hopefully) tomorrow, when the James Webb Space Telescope rides into Earth orbit. Webb has five times the light-gathering power of the 31-year-old Hubble Space Telescope. While Hubble detected mostly visible light, Webb will detect mostly non-visible infrared "light" having a slightly longer wavelength. This is advantageous because the universe has expanded during its 13.8-billion-year history, stretching light waves into infrared waves.
For a glimpse of this mind-boggling instrument's technical finesse, consider its primary mirror that reflects incoming infrared to a secondary mirror and then to a detector. It's made of 18 hexagonal mirrors fitted together in a honeycomb pattern --a perfect mirror covering 357 square feet. The mirrors are made of beryllium coated with a very thin layer of highly reflective gold that was put onto the surface by "vacuum vapor deposition" in which small quantities of gold are vaporized and deposited on the beryllium surface. A thin layer of glass was then deposited on top of the gold layer to protect it from scratches. The total weight of the gold, a heavy metal, was just 50 grams or 1.8 ounces -- the weight of a golf ball!
After launch, project engineers will experience 30 days of terror as Webb unfurls its solar electric panels, its communications antenna, its huge sunshield and its mirrors. It must then maneuver itself into position orbiting Earth at a gravitational balance point called "L2," which is 1.5 million kilometers from Earth, too far to be repaired by visiting astronauts. So it's got to work flawlessly from the start. Unable to be refueled, it will have a limited lifetime. The limiting factor is the propellant that drives its repositioning thrusters, which will run out in 5 to 10 years.
During those years, Webb will report to Earth with data bearing on everything from the era when the first stars began shining, to the mysterious unseen dark matter that comprises 85 percent of the universe's matter, to deeper understanding of our own solar system, to conditions on other planets orbiting other stars, and whether these planets might provide a habitat for life.
Webb should spot evidence for the first stars formed directly from the simplest atoms, hydrogen and helium, created during the Big Bang's first few minutes. Some 200 million years later, as the universe expanded and thus cooled, hydrogen and helium gas fell together gravitationally to form stars. These early stars were possibly 1,000 times more massive (heavier) than our sun, causing them to "burn" (i.e. fuse their atomic nuclei together) rapidly and furiously, which exhausted their fusion fuel in a mere few million years. Hundreds of millions of years later, the first galaxies formed.
What about life in the universe? Astronomers discovered the first "exoplanets" around other stars during the 1990s. We have now found thousands and regard them as the norm around other stars. Webb will get to know them better, investigating how they are born, dissecting their material, and, most pertinently, studying their atmospheres. The idea is to detect a planet as it orbits directly in front (as seen from Webb) of its star. Starlight passing through the planet's atmosphere is altered by being partially absorbed. Webb receives this light and studies its "spectrum," from which scientists can deduce many chemicals in the exoplanet's atmosphere.
Hubble and other telescopes have already detected water vapor, methane and carbon monoxide in exoplanet atmospheres. Webb will detect these and many more, some (like water) essential for life as we know it and others (like methane) consistent with life. One knowledgeable scientist says "Webb will blow the door wide open" on exoplanet chemistry. Webb will sniff out the atmospheres of rocky planets similar to Earth but might not be capable of detecting direct signs of life such as oxygen or chlorophyll. With the help of a shield that blocks the overwhelming glare from an exoplanet's star, Webb will even be able to photograph some exoplanets.
Although Webb will capture spectacular exoplanet data, convincing evidence of life on other worlds will probably have to await an even larger space telescope.