The Hubble Telescope has given us astonishing images of distant stars, but despite its accomplishments, it has a limited view of the heavens. Scientists and engineers are hard at work on a larger, more powerful successor — the James Webb Space Telescope. Hubble has had an impressive run — it’s been used to detect clouds on distant planets, find evidence of planets with glass rain, and image a star near the end of its life — but the Webb will be able to do more. The researchers behind Webb hope to probe the early universe by gathering some of the earliest, most distant light. And engineers building the telescope have recently completed a major milestone: finishing and delivering the mirrors that will be pieced together for Webb’s huge primary mirror.
That mirror will be a stunning a 21 feet high, made of 18 smaller hexagonal mirrors. It’ll be used to help the telescope capture images of the night sky and also break down the spectrum of the incoming light to analyze properties of galaxies, stars, and even exoplanet atmospheres. The Webb venture isn’t just an American endeavor, but is part of an international collaboration that includes NASA, the European Space Agency, and the Canadian Space Agency.
A telescope to probe the early universe
The lead scientist on the project, Nobel laureate John Mather, says that agencies wanted a new telescope because "[researchers] believed when they built [Hubble], when they designed it, that it would be able to see the first galaxies forming in the early universe. They found a big surprise — they couldn’t." The reason being that the oldest light in the universe has undergone a doppler shift — much like the pitch of a car horn shifts as it passes you, light shifts due to the expansion of the universe. The Hubble telescope can detect the same colors the human eye can detect and a little beyond, but it can’t detect this stretched-out, infrared light from the early universe.
Indeed, detecting infrared light poses some daunting challenges. A telescope like Hubble generates its own heat and is exposed to the rays of the sun, both sources of of infrared light. These factors could drown out the weak infrared signals from far-away galaxies. To keep cool, the Webb will orbit a million miles from Earth — four times further than the moon. At its orbital point, the Earth, moon, and sun will all be in the same direction, so they can all be shaded with one sunshade.
Each of the mirrors take a large amount of effort to construct, and it took years to actually make them. The Webb has to be very cold to operate, but materials can warp with temperature change. The researchers selected the metallic element beryllium because it will warp very little with falling temperatures. Even still, the process of constructing the mirrors required much care and many iterations: after polishing the mirrors at room temperatures, engineers cool it down to see how it warps, and then try another polish to compensate for this warping.
The final versions of those mirrors have recently been delivered to the Goddard Space Flight Center. But despite that major milestone, Webb won’t be ready for liftoff until 2018. There is still testing needed for the telescope’s existing components, and construction for the rest of the parts that will comprise the observatory and the rockets, among other elements.
Once in space, Webb will probe the first stars and galaxies, the birth of stars, and Earth-like planets. Scientists are looking for plenty of things, but Mather himself hopes to peer toward the unknown. "The real hope is we’ll get some big surprises," he said. And by looking where no other telescope can see, Webb has a good chance of surprising us.