The James Webb Space Telescope: Science on the Edge
Artist's concept: Envisioning the telescope in operation
The James Webb Space Telescope promises to open up new horizons as we gaze to the edges of the visible universe. Webb is an infrared telescope, seeing in a wavelength of light difficult to observe from Earth. It will be larger than any space telescope ever placed in orbit. The telescope will function at temperatures just tens of degrees above absolute zero — the temperature at which even atoms are so cold they cannot move.
Its launch in 2018 will help astronomers answer some of the most pressing questions in astronomy, such as, How did the first galaxies form? How do stars, galaxies, and planets come into existence? Are we alone in the universe?
Infrared light is invisible to our eyes, but not to Webb's powerful instruments. Orbiting 1 million miles from Earth, the Webb telescope will peer back to the time when new stars and developing galaxies first began to light up the universe billions of years ago. Webb will see light from the early universe that has been stretched as it travels across the expanding fabric of space. It will see through clouds of dust to the warm, infrared-emitting objects hidden within. Our view of the universe will expand as Webb gazes on previously unexplored territory.
Why an infrared telescope?
Two views of the Horsehead Nebula: In visible and near-infrared light
Infrared is light beyond the red end of the visible-light spectrum. It is invisible to the human eye. However, if we can detect it using special instruments that observe infrared light, we gain valuable information about the workings of the universe.
Astronomers prize infrared light for several reasons.
First, the expansion of the universe causes all galaxies to move away from one another. Visible light from the most distant objects gets stretched as it travels through space, turning into infrared light. To see the farthest and earliest galaxies in the universe, astronomers have to look at the stretched, once visible light that reaches Earth in the form of infrared light.
Two views of the Whirlpool galaxy: In visible and near-infrared light
Second, infrared light penetrates the dark clouds of dust present in the universe. Everything gives off some infrared light, but warm objects — those at room temperature — emit large amounts. We see this effect on Earth. Night-vision goggles rely on infrared vision to form an image of warm bodies. Certain snakes also detect their prey with infrared-sensing organs. Dust clouds block visible light, but not infrared light. By detecting infrared light, astronomers can see through the clouds to the warm objects within.
Third, some things mostly emit infrared light. Not all objects glow in visible light, but even the dimmest objects give off some infrared light. Older planets, dust around stars, the early stages of star formation, and clouds of dust drifting in space are all visible in infrared light. In many cases, they are easier to spot in the infrared than in visible light.
By studying the universe with Webb's infrared vision, our understanding of space and our place in the universe will be reshaped by the telescope's discoveries.
Massive stars in the early universe
The universe's first stars are believed to be 30 to 300 times as massive as our sun and millions of times as bright. They would have burned for only a few million years before dying in tremendous explosions, or "supernovae." These explosions ejected the chemical elements of the massive stars outward into the universe, enriching later generations of stars. The dying stars then collapsed into black holes or were destroyed.
Scientists suspect the newborn black holes gobbled up gas and stars around them, becoming the extremely bright objects called "mini-quasars." The mini-quasars may have grown and combined with other mini-quasars to become the huge black holes found in the centers of galaxies. Webb will try to find these supernovae and mini-quasars to help astronomers put theories of early universe formation to the test.
Hunting for the first galaxies
Hubble Ultra Deep Field: In near-infrared light
Galaxies are where the action is. They're where most star birth, life, and death takes place. The production of heavy elements, the formation of planets, and, eventually, the beginning of life also take place in galaxies.
The Webb telescope is designed to study the small groups of stars that make up the early building blocks of today's galaxies. Webb will reveal when galaxies first appeared and will provide information about their environment. Webb will analyze the heavy elements produced by supernovae. It will examine the exchange of material between galaxies and the gas, dust, and space between galaxies, called the intergalactic medium. The telescope will help scientists test the theory that small galaxies cluster together and merge to form larger galaxies. It will investigate the relationship between the evolution of galaxies and the development of the huge black holes at their centers.
The birth of stars and planets
A planet orbits the star, Fomalhaut
Stars and planets form together from clouds of gas and dust within galaxies like our Milky Way. Portions of these clouds collapse under their own gravity into denser and denser clumps to create the cores of just-forming stars. A small amount of dust and gas remains free of the stars and combines, forming flattened, pancake-shaped disks around the young stars. Within a few million years, this disk material collects into large bodies and clumps of debris, forming giant and rocky planets — perhaps like those in our own solar system.
Webb will probe deeply into the dusty disk that surrounds and hides young stars. The telescope can explore the structure of this material to determine the conditions in the disk at the time of planet formation. These observations will help unravel the questions that surround the birth and early evolution of stars and the origins of planets, including the mysteries of the earliest objects in our own solar system.
Seeking living planets
An exoplanet orbits its parent star
Planets exist outside of our solar system, orbiting distant stars. If other planets exist, could life have taken hold elsewhere in the universe? Learning about the formation and evolution of planets — including our own — will help us understand whether other stars could develop life-bearing planets.
Webb will investigate the nature of Jupiter-like planets in other solar systems to help astronomers determine how their formation might affect the creation of rocky planets like Earth.
Scientists believe that the disks of dust and debris found circling certain stars may be the beginnings of new solar systems. Webb will study these disks around young stars to look for similarities and differences between their composition and the materials in our own solar system.
Today's telescopes can find planets by watching the changes in the light of a star that occur as a planet passes in front of it. Webb will be able to determine the sizes of the planets and even the chemical makeup of their atmospheres, providing a rich survey of extrasolar planetary systems.
Our solar system beginnings
Jupiter: In near-infrared light
Webb will study the atmospheres of solar system planets such as Mars. The telescope also will observe moons, including Titan, to analyze their chemical makeup. Webb's observations of the giant planets, such as Jupiter and Saturn, will give astronomers a better picture of the planets' seasonal weather. The telescope's infrared vision also will be useful for studying the surfaces of planets and moons in the outer solar system, and those obscured by cloud layers.
The New Horizons Pluto flyby provided astronomers with new information about the dwarf planet Pluto, located in the outer solar system. Astronomers plan to use the Webb telescope for follow-up observations of Pluto. Webb also will be able to measure the surface chemistry of Pluto, its moons, and many other icy objects that reside in the Kuiper belt. The Kuiper belt is a large region of ancient, icy rocks that are the building blocks of our solar system's makeup 4.5 billion years ago.
The Webb telescope also will closely examine comets, which are made of material left over from the formation of the planets. Scientists can compare the makeup of comets with planet- and star-forming dust and debris to learn how solar system objects form and evolve. Comets are also one possible supplier of the Earth's water, seeding the planet with water vapor through millions of impacts over billions of years. Webb will help confirm or dismiss this theory by examining comets' composition.
Future, unknown science
When scientists sent Hubble into space, they never expected to find that the expansion of the universe was speeding up. Theory said it should be slowing down. Nor did they realize they would have obtained front-seat tickets to watch a comet crash into Jupiter or see a Mars global dust storm.
Webb's true value will be known only after it reaches its place among the stars. The greatest science it reveals may be the questions no one has thought to ask yet, the discoveries so unknown, so unexpected, that they open new realms of thought, new floods of questions. Webb's greatest science may very well lie in areas that have yet even to be imagined.