There's a period of time after the Big Bang, when the universe was in its infancy and the very first stars were blinking into existence, that remains one of the most mysterious chapters in the history of the cosmos.
If astronomers could study those chaotic, heady days of the early universe, they could begin to unravel how the cosmos evolved over more than 13 billion years. They might finally understand what extraordinary forces gave rise to stars, galaxies, black holes and planets — including worlds beyond Earth that may support life.
Yet even with the most sophisticated observatories in space and on the ground, scientists lacked the means to observe the oldest and most distant objects in the universe.
That is, until now.
NASA is set to launch into space humanity's largest and most powerful telescope, a $10 billion behemoth called the James Webb Space Telescope. The tennis court-sized observatory, slated to lift off Saturday from a European spaceport in French Guiana, will be able to see deeper into space and in greater detail than any telescope that has come before it.
NASA has billed the mission as an "Apollo moment" — a giant leap forward that could revolutionize our understanding of the universe and humanity’s place in it.
"It's kind of a cliché to say that it’s going to change the course of astronomy, but it might very well do that," Marcia Rieke, an astronomer at the University of Arizona, said.
Rieke has spent the past 20 years leading the development of one of the Webb telescope's four main instruments, a specially designed infrared camera known as NIRcam. She said Webb could unlock mysteries of the early universe, from as far back as 100 million years after the Big Bang. It could also observe exoplanets with instruments sensitive enough to study their atmospheres, looking for potential biosignatures of alien life.
For all its potential benefits, the mission is also one of NASA's most daring.
After launch, the Webb telescope will spend about a month journeying to a point in orbit around the sun that is about 1 million miles away from Earth.
The observatory's destination is known as the second Lagrange, or L2, point and was chosen because the telescope can remain in a stable orbit with one side of the telescope permanently facing Earth and the sun. This helps shield the telescope's instruments from heat and light that could interfere with its observations.
But at a million miles away, NASA won't be able to send astronauts to the telescope to make upgrades or repairs if anything goes wrong. Astronauts famously visited the Hubble Space Telescope in low-Earth orbit on five separate servicing missions between 1993 and 2009. That won't be an option this time, said Greg Robinson, Webb’s program director at NASA.
"There's no help on the way," Robinson said. "Once it leaves the planet, it's on its own."
Next-generation space telescope
The James Webb Space Telescope is a collaboration between NASA, the European Space Agency and the Canadian Space Agency. First proposed more than 30 years ago, the observatory is designed to help astronomers piece together how the modern universe came to be.
But the project has not been without controversy. Over the course of its development, the telescope ran billions of dollars over budget and was finished more than a decade behind schedule. For the thousands of scientists and engineers around the world involved with the project, it has been a long and often bumpy journey.
Now, Webb is finally ready for launch.
The observatory will build on the legacy of the iconic Hubble Space Telescope, which has been operating since 1990. Though Hubble is responsible for decades of scientific discoveries and some of the most jaw-dropping images of the cosmos, including the famed Pillars of Creation, the telescope is limited in what it can see — and how far.
The Webb telescope’s primary mirror, which collects and focuses light from objects in the cosmos, will be the largest to fly in space.
Measuring more than 21 feet across, Webb's mirror is nearly three times the size of Hubble's, allowing it to observe more of the cosmos and in greater detail. Altogether, the Webb telescope will be 100 times more powerful than Hubble, Robinson said.
In other words, if Hubble opened a window to the universe, then Webb will likely kick down the door.
"We knew that there were going to be things that we find where Hubble gave some tantalizing clues but didn’t have the right suite of capabilities to pursue," Rieke said.
But the impressive size of Webb's mirror was also one of the mission's greatest design challenges. To fit inside the rocket for launch, the mirror needs to be folded up and then subsequently unfolded once in space. Each of the 18 gold-coated, hexagonal segments requires ultraprecise alignment to function as one single mirror.
The telescope's enormous sunshield will also unfurl once the observatory reaches space. The diamond-shaped sunshield is designed to keep the telescope's mirror and instruments ultracold, allowing them to pick up the faintest heat signals in the universe without interference from Earth or the sun.
Seeing the past
Webb's ability to detect distant stars and galaxies owes to the telescope's infrared "eyes," which probe beyond the range of human sight and beyond other telescopes, including Hubble, that see primarily visible light.
The longer wavelengths of infrared light can pierce through thick veils of cosmic gas and dust that might otherwise obscure some celestial objects.
Infrared instruments are also better suited for trying to detect the universe's earliest stars and galaxies. Telescopes essentially function as time machines because it takes time for light to travel through space. As such, light that reaches the Webb telescope from the most distant galaxies don't tell of present conditions but rather offer insights into how the universe was billions of years ago.
Since the universe is expanding, light from the earliest stars and galaxies is stretched, shifting into longer infrared wavelengths undetectable by Hubble or the human eye.
"We will see things that we've never known were there, and we'll see things we've known about differently and better," said John Mather, the Webb telescope's senior project scientist at NASA's Goddard Space Flight Center.
Mather, who has been involved with the Webb telescope for the past 26 years, called it a once-in-a-generation mission, adding that the telescope's discoveries will "keep astronomers busy for decades."
"We'll be able to write a much better history of the expanding universe. We'll see how it happened that galaxies have black holes in the center and how it's possible that a planet can exist that is capable of supporting people," he said.
But perhaps more exciting are the new questions that Webb could raise — ones that scientists didn't even know to ask. Mather said he hopes the mission will inspire curiosity in the general public for generations to come.
"Science is about discovery and the unknown," Mather said. "We're always puzzling our way through the unknown, and I want to invite people to come along and join us in that quest."