Astronomers are hoping that the Webb will be able to collect light that is very far away from us and is moving still farther away. The universe has been expanding ever since the big bang got it started, but scientists reckon that if the telescope is powerful enough, they just might be able to see the birth of the first galaxies, some 13.5 billion years ago.
“This is similar to archaeology,” says Harvard astrophysicist Avi Loeb, who helped plan Webb’s science mission. “We are digging deep into the universe. But as the sources of light become fainter and farther away, you need a big telescope like the James Webb.”
Named for a former NASA director, the 21-foot-diameter Webb telescope will be 100 times as powerful as the Hubble Space Telescope, which was launched in 1990. Although Hubble wasn’t the first space telescope, its images of far-off objects have dazzled the public and led to breakthroughs in astrophysics, such as determining how fast the universe is expanding.
The Webb will be both bigger and located in a darker part of space than Hubble, enabling it to capture images from the faintest galaxies. Four infrared cameras will capture light that is moving away from us very quickly and that has shifted from the visible to the infrared spectrum, described as red-shifted. The advantage of using infrared light is that it is not blocked by clouds of gas and dust that may lie between the telescope and the light. Webb’s mirrors are covered in a thin layer of gold that absorbs blue light but reflects yellow and red visible light, and its cameras will detect infrared light and a small part of the visible spectrum. As objects move away from us, the wavelength of their light shifts from visible light to infrared light. That’s why the Webb’s infrared cameras will be able to see things that are both far away and moving away from us.
In the meantime, scientists such as Sara Seager of MIT, who studies exoplanets that revolve around distant stars, are imagining the discoveries that will occur once Webb directs its mirrors toward deep space. As a planet moves in front of a star, researchers hope to see the fingerprints of its atmosphere, which absorbs starlight. By analyzing the chemical spectrum of the light, they may be able to determine the atmosphere’s composition. Oxygen has a spectral fingerprint, as does methane, carbon dioxide and other gases found in atmospheres.