How NASA's most powerful telescope ever will reveal unseen corners of the universe

The Christmas launch for the long-delayed James Webb Space Telescope goes off without a hitch. Here's everything you need to know about the mission.

Monisha Ravisetti Former Science Writer
Monisha Ravisetti was a science writer at CNET. She covered climate change, space rockets, mathematical puzzles, dinosaur bones, black holes, supernovas, and sometimes, the drama of philosophical thought experiments. Previously, she was a science reporter with a startup publication called The Academic Times, and before that, was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. When she's not at her desk, she's trying (and failing) to raise her online chess rating. Her favorite movies are Dunkirk and Marcel the Shell with Shoes On.
Monisha Ravisetti
7 min read

After many delays NASA's revolutionary James Webb Space Telescope finally launched on Christmas morning as astronomers worldwide held their breath watching the instrument head to space aboard an Ariane 5 rocket. The ambitious successor to the Hubble telescope lifted off from South America and promises to forever alter our knowledge of the universe.

Decades of work led to the launch at 4:20 a.m. PT, or 9:30 a.m. local time at the European Space Agency launch base in French Guiana. Prior to that successful launch, tensions were high.

"Twenty years of my life will all come down to that moment," said Mark Voyton, Webb observatory integration and test manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland. But after a launch that went "exactly as expected," according to ground control, an eruption of exhilarated applause in the mission operations center welcomed the next chapter of astronomy.

Armed with unprecedented infrared imaging power integrated with state-of-the-art machinery, Webb will travel 1 million miles (1.6 million kilometers) from Earth to give us access to the deepest, darkest and oldest secrets of space. 

It's equipped to peer past the cosmic dark ages and document the first specks of light to flood the universe, see stars form behind dust clouds that Hubble couldn't penetrate, zoom into supermassive black holes with unparalleled precision, detect galaxies invisible to the naked eye and begin cataloging planetary systems in search of habitable exoplanets.

While other space probes, such the 1989 Cosmic Background Explorer, have technically studied a greater distance into the universe than Webb will, this telescope "was designed not to see the beginnings of the universe, but to see a period of the universe's history that we have not seen yet," said John Mather, senior project scientist for the James Webb Space Telescope.


A timeline of the universe. Webb will offer us access to the region before what scientists call the cosmic dark ages of the universe.


Think of it as the difference between looking up at the stars from a light-saturated New York City, then from a dark forest glen. Standing beneath the shadows of dense greenery, you'd see a myriad more sparkles even though you're viewing the same sky -- you're just viewing it unfiltered by light pollution. 

Imagine a lens that can look out into the depths of space, unfiltered. One day, Webb could even help us answer a potentially chilling question: Are we alone in the universe? Read on to learn why NASA's James Webb Space Telescope might well be the most important mission of our generation.


A 2017 image of Webb in "full bloom." The 18-segmented gold mirror is designed to capture infrared light from the first galaxies that formed in the early universe and will help the telescope peer inside dust clouds where stars and planetary systems are forming today.

NASA/Desiree Stover

Telescope or time machine?

Every time you look at the moon, you're looking back in time because light doesn't travel instantaneously. The farther the light source, the longer it takes for its light to reach you.

Down on Earth, if someone across the room switched on a lightbulb, it would take an infinitesimally short time for its illumination to hit your eye. But if someone were to stand on the moon and switch on a lightbulb, it would take 1.3 seconds for you to see it back on Earth. In essence, every time moonlight reaches your eye, you're looking back in time by 1.3 seconds -- and that's just the moon, some 238,855 miles (nearly 384,400 kilometers) away.

The James Webb Space Telescope can look much farther into deep space, about 13.7 billion light-years away, which means it can look 13.7 billion years back in time. That's just 100 million years after the universe was born.  


An artist's conception of the James Webb Space Telescope flying through space.

Adriana Manrique Gutierrez, NASA Animator

As it searches for clues to what happened right after the Big Bang, it will use natural cosmic flashlights called quasars to watch the epoch unfold. Thought to be powered by supermassive black holes, quasars live in the centers of galaxies and emit immensely luminous light.

"If you want to study the universe, you need very bright background sources," said Camilla Pacifici, who is affiliated with the Canadian Space Agency and works as an instrument scientist at the Space Telescope Science Institute in Baltimore. "A quasar is the perfect object in the distant universe because it's luminous enough that we can see it very well."


An artist's concept of a galaxy with a brilliant quasar at its center. Using the unique capabilities of Webb, scientists will study six of the most distant and luminous quasars in the universe.

NASA, ESA and J. Olmsted (STScI)

Plus, thanks to a long list of high-intensity equipment, Webb won't just be taking pictures of the distant universe as is; Webb is programmed to employ infrared imaging.

Infrared signatures

Arguably the most crucial feature of Webb is its infrared imaging capabilities -- the primary reason it can capture such rich, unfiltered glimpses of the ancient universe.

As cosmic bodies get farther away from Earth, along with the rest of space's fabric, the light illuminating them stretches out simultaneously, resulting in a phenomenon called redshift. Redshift has to do with the way light on the electromagnetic spectrum exists in wavelengths, which sort of look like curvy zigzags. 

On one end of the spectrum, we have blue light, and on the other end, red light. Blue light wavelengths are shorter, so you can think of them as having a ton of narrow, pointy waves on the zigzag. Red light has longer, stretched-out wavelengths. 

As the universe expands, quasars' wavelengths of blue light slowly stretch out like pulling on a rubber band -- and as they get longer, they become redder. Once those wavelengths get really far on the red end of the spectrum, they'll enter what's called the infrared light region. 

Unfortunately, the human eye can't see infrared light, and Hubble can see only a portion of it. Webb is designed for the job.


A comparison of Hubble's visible and infrared views of the Monkey Head Nebula. While Hubble has some infrared capabilities, they're nothing compared to Webb's.


It will pierce through dust clouds to study objects in space illuminated by light in the infrared region. Because infrared information can also reveal physical properties, Webb will identify whether molecules like water are present on faraway planets. And that's just the beginning.

While there are some hypotheses about what Webb might find, like the way particles once reionized to form stars, the discoveries it makes will likely be of things we never even thought to ask about.

"We think that the tiny ripples of temperature [other telescopes like COBE] observed were the seeds that eventually grew into galaxies," Mather said. But because those probes weren't armed with infrared imaging, "we don't know exactly when the universe made the first stars and galaxies -- or how, for that matter. That is what we are building JWST to help answer."

Breakdown of Webb's specs and its role in finding alien life

For the unfiltered effect, the international team behind the spacecraft integrated many of Webb's instruments with its high-tech infrared imaging processors. Here are some specifics.

Webb's mirror: 21.3 feet (6.5 meters) across, with 18 gold-plated hexagonal segments that collect infrared light. NASA calls it a "light bucket."

Sunshield: A five-layer metal umbrella the size of a tennis court to protect the probe from the heat of the sun, the Earth and the moon.

Near-Infrared Camera (NIRCam): Webb's primary imager that will detect the earliest stars and galaxies forming.

Near-Infrared Spectrograph (NIRSpec): This tool can use infrared information to inform scientists on physical properties like chemical composition and temperature of galactic bodies.

Mid-Infrared Instrument (MIRI): This has both a camera and spectrograph that can detect objects in the mid-infrared electromagnetic region.

Near-Infrared Imager and Slitless Spectrograph (NIRISS): This one's thought to be particularly  useful in exoplanet detection.

Fine Guidance Sensor (FGS): Used for navigation.

A 3D rendering of how James Webb will look in space once fully deployed.

NASA's Goddard Space Flight Center Conceptual Image Lab

Data sent back to Earth from the James Webb Space Telescope will promptly be available to researchers across the globe. A wide array of minds will heavily scrutinize it to unravel mysteries like: Are there early universe stars that collapsed into black holes we haven't studied before? Is there life anywhere else in the universe? Are there planets beyond our Milky Way galaxy conducive to supporting life in the future? 

The latter two come into play when Webb starts using a different approach to infrared detection -- heat signatures.

"If we see the signatures of thermochemical equilibrium, we would conclude that the planet is too hot to be habitable," Renyu Hu, a researcher at NASA's Jet Propulsion Laboratory, said in a statement. "Vice versa, if we do not see the signature of thermochemical equilibrium and also see signatures of gas dissolved in a liquid-water ocean, we would take those as a strong indication of habitability."

Lifting off a priceless mission

Equal to this telescope's grandeur is its complicated -- and expensive -- deployment sequence. Its countdown signified the culmination of decades of engineering, planning and over $9.8 billion in funding.

Once the liquid-fueled engine of the Ariane 5 roared and the launch vehicle entered space, the Webb telescope was exposed to the void, then detached. Then, it successfully unfurled its solar array and began charging up to continue its decade-long journey. 


The Ariane 5 rocket on which Webb will be launched in French Guiana in northeast South America.


Over the following 30 days, while slowly unfurling from its origami-like folds, it will travel to an orbit around the sun at what's called the second LaGrange point. This spot is special. From there, Webb has a clear, uninterrupted view out into space, and its sunshield can protect it from the light and heat of Earth, the sun and the moon. 


Webb will orbit the sun 1.5 million kilometers (1 million miles) away from the Earth at what's called the second Lagrange point, or L2. Note: This graphic isn't to scale.


Because infrared light can sometimes be detected as heat, Webb must be kept at a low temperature. 

NASA said it will have to conduct about six months of other scientific operations, like optics checks and calibrations of Webb's instruments, before getting into the thick of the mission. 


NASA engineer Ernie Wright looks on as the first six flight-ready primary mirror segments of Webb are prepped to begin final cryogenic testing at NASA's Marshall Space Flight Center.

NASA/MSFC/David Higginbotham