Even the universe was young once. Someday soon, astronomers hope to snap a few of its baby pictures.
The tool they'll use to do it is the James E. Webb Space Telescope, set to launch into space atop a European Space Agency rocket in 2011.
Once it's up and running--it is now being built by Northrup Grumman for NASA, the European Space Agency and the Canadian Space Agency--astronomers hope to peer back in time to when the universe was a toddler, a mere 200 million years after its birth in the "Big Bang" that took place [some 15 billion years ago].
Space telescopes act like time machines because the objects they look at are so far away that the light has taken billions of years just to get to the telescope, even though that light has been traveling at the speed of, well, light. And while scientists have a good understanding of what happened during the first 100 million years or so of the universe's life, there's a big blank spot in its timeline from that point to about a billion years after the Big Bang. Their hope is to see examples of the earliest stars and galaxies and study their evolution and the production of elements, which in turn leads to better understanding of the origins of life.
What will astronomers see? Things that are as yet only theorized. "We have lots of stories that say there should have been a first generation of stars," says John Mather, NASA's senior astrophysicist working on the Webb telescope. These primordial stars--known as "population 3" stars, would have formed early in the history of the universe out of pure hydrogen and helium, burned for a short three million years or so and then exploded.
"We don't have any direct evidence that these stars existed, but we can see traces of them in the cosmic background radiation," Mather says. That background radiation is a form of electromagnetic radiation that is seen in every direction in the universe, and considered the best available evidence for the Big Bang theory, which holds that the universe came into being in an unbelievably massive explosion [some 15 billion years ago].
But seeing all this isn't easy. The Hubble Space Telescope, in orbit around Earth since 1990, has given us a good look at the universe going back to about 400 million years after the Big Bang, Mather says. The Webb Telescope will differ from Hubble in many important ways that will give it a better vantage point.
First, it will be positioned farther away from Earth than the Hubble, says Eric Smith, program scientist on the Webb telescope project. The Hubble orbits us at an altitude of 375 miles, within easy range of the Space Shuttle and other manned orbital vehicles. Since it was launched, astronauts have visited the Hubble Telescope on repair and maintenance missions four times, the last in 2002. A fifth mission was recently cancelled in the wake of last year's in-flight loss of the Space Shuttle Columbia (see "Columbia's Gone But Space Exploration Goes On").
Such maintenance missions won't be possible with the Webb. It will be placed at a point in space a million miles away from Earth, about four times as far away as the Moon, at a point called L2. That's one of five so-called "Lagrangian points" (named for an 18th Century mathematician who discovered them) in space where the forces of gravity are in a balance and will allow the telescope to stay in one place.
Placing Webb so far away helps with two key problems, Smith says. L2 is cold. The Webb telescope will essentially be a great big infrared camera in space, and the colder it is, the better. Being closer to Earth, which is heated by the sun, would hinder the camera's ability to detect the faint infrared images from so far away. Mather says the temperature at L2 is about 35 degrees Kelvin, or about 370 degrees below zero on the Fahrenheit scale. That's so cold that the telescope itself won't emit enough heat to foul up its own ability to detect faint IR radiation. Protecting the telescope from sunlight will be a shield approximately the size of a tennis court.
The core component of the telescope is a 50-million pixel digital camera, which when completed will be the biggest, highest resolution NASA has ever had. Central to the camera will be a huge mirror about 20 feet in diameter made of beryllium and consisting of 18 individual hexagonal parts, each about four feet across.
Its distance from Earth also means the Webb telescope won't need the metallic tube that gives the Hubble its distinctive appearance. That cuts down on the overall size and weight, making it easier to launch aboard a rocket. The Webb telescope will be a little more than half the weight of Hubble.
Controlling how light is recorded by the camera will be an array of microshutters--akin to the shutters on a conventional camera that open and close in order to let light in--that will let light into the telescope from different areas of space at different times. Each shutter is about the diameter of a human hair and will open and close individually in order to precisely control light exposure. The result, Mather says, is a vast improvement in image quality and contrast.
Once inside the telescope, Mather says, the light is diverted to a spectrometer, which breaks it up into different colors of the light spectrum where it can be analyzed. Based on that analysis, astronomers can tell a great deal about an object's temperature and its chemical composition and density.