These six glimmering hexagons are part of the James Webb Space Telescope’s primary mirror. There are 18 segments in total, made from beryllium and coated in a golf ball’s worth of 24-karat gold, which helps reflect infrared light.
On this day 25 years ago, the Hubble Space Telescope hitched a ride to low-Earth orbit aboard space shuttle Discovery. It was the biggest, baddest space telescope ever launched, designed to stare back in time and tease cosmic secrets from the stars.
But, as in all good fairy tales, trouble soon followed. When Hubble’s first images came back to Earth, it was clear the 1.5-billion-dollar instrument—more than two decades in the planning—couldn’t see straight. The images were terrible. Hubble’s primary light-gathering mirror had been made perfectly, precisely wrong, the defect undiscovered until those first blurry stars appeared.
It would take three years and another shuttle visit to make the first fix of Hubble’s vision. And we all know what happened next: Not only did Hubble go on to make world-class, truly groundbreaking observations, it captivated millions of Earthlings with spectacular images of space. Hubble’s ghostly nebulae, glittering stars, and those tremendous, faraway galaxies have been printed on everything from refrigerator magnets to posters, and even tattooed on human skin.
It’s still in excellent shape, but our beloved eye in the sky can’t stare into space forever. Soon, another giant telescope—even bigger than Hubble—will be blasting off, ready to pick up where Hubble left off.
“We’re going to find all sorts of new things—and when we do that, we’re going to change the astronomical landscape again,” says Space Telescope Science Institute’s Jason Kalirai, project scientist for the upcoming James Webb Space Telescope.
Hubble's Big Sister
In some sense, the James Webb Space Telescope is a successor to Hubble. It's a major space-based, general-purpose observatory, says NASA’s Jennifer Wiseman, senior project scientist for Hubble.
“But in another way, it really is almost a sister to Hubble,” she says. She and others hope both telescopes will be operating at the same time, at least for a little while, so scientists can aim the sisters' eyes at some of the same objects.
Plagued by delays and cost overruns, but now set to launch in 2018, Webb is designed to peer farther back in time than any instrument has so far. Its infrared eye will be able to gather light from just 200 million years after the universe was born, an era when the first stars and galaxies were just taking shape, as well as study planets around other stars—and even the planets around our star. Unlike Hubble, it will do all of this from a perch about a million miles from Earth.
Named after the NASA administrator who played a key role in the Apollo program, the James Webb Space Telescope is huge. Its primary mirror measures 21 feet (6.5 meters) across (compared to Hubble’s 8-foot mirror) and looks like a giant insect’s eye, with 18 beryllium hexagons coated in a thin layer of gold. The whole assembly will be folded up for part of the two-month journey to the telescope’s destination, and will unfurl like a piece of high-tech space origami.
The plan isn’t without risk, though. When Webb leaves Earth, it will set a course for a point nearly a million miles away, known as Lagrange Point 2, or L2. Its destination is one of five spots where a spacecraft can pretty much park itself and stay in the same place relative to the sun and Earth. It’s dark and cold (and a sunshield will help make it colder) —but it’s so far away there’s no hope of rescue if something goes wrong.
“There’s some tension associated with it,” says Robert Williams of the Space Telescope Science Institute. “If there are failures, we have to come up with workarounds.”
Seeing in a New Light
Once on its way, the telescope will begin chilling itself to fewer than 50 degrees above absolute zero. This will allow it to observe the cosmos in a different light than Hubble. While Hubble’s powers of perception are especially strong in ultraviolet and visible wavelengths, Webb will see the sky in infrared. Slightly longer than the wavelengths human eyes can see, infrared light opens our window to the universe just a bit wider.
“The dust grains in space prevent us from seeing some things,” says Webb’s senior project scientist John Mather, of NASA’s Goddard Space Flight Center. But, he says, dust-shrouded newborn stars and planets won’t be able to hide from Webb. “It will let us see through those opaque clouds and see the stars being born.”
What's more, we can see farther back in time in infrared. Light stretches as it travels through space, and light that’s been on the road for billions and billions of years is stretched so much it leaves the visible spectrum and crosses the threshold into the infrared—so capturing infrared light will turn Webb into the most powerful time machine yet.
“It’s a tool for exploring the unknown,” says Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics.
Scientists can predict some of what the telescope is likely to see. It’ll spy on stars being born and planets orbiting other stars. Webb will also attempt to study the earliest stars and galaxies, which Mather says will probably look like little smudges in the dark. “They’re not going to be especially beautiful, except in the mind’s eye,” he says.
But a lot of what the telescope will discover remains a surprise. “Our imagination is not powerful enough to substitute for observation. We’ve got to go look,” Kirshner says. “It will be astonishing to me if we don’t find something really surprising and new.”
He and others suspect Webb will be every bit as captivating as Hubble. After all, who knows what hides in those distant reaches of the cosmos, where matter and energy could come together in ways we can’t even imagine?
“The universe is really, really big, and it’s often just beyond the reach of our ideas and our instruments,” says University of Chicago cosmologist Michael Turner. Now, finally, we’re starting to catch up, he says.
"This has got to be one of the most exciting times to be an astronomer," Turner says. “The big questions we’re hoping to answer are so diverse and so basic: Is there life elsewhere in the universe? What’s the universe made of? Why is it speeding up? What’s its destiny?”
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