A Cosmic Photographer: Decades of Work to Get the Perfect Shot
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- Category: Research News
- Published: Friday, August 29 2025 01:40
John Mather, a College Park Professor of Physics at the University of Maryland and a senior astrophysicist at NASA, has made a career of looking to the heavens. He has led projects that have revealed invisible stories written across the sky and helped us understand our place in the universe.
He left his mark on physics by uncovering the earliest chapter of our universe’s story. He and his colleagues captured an image of the invisible remains of some of the universe’s first light. To get the image, they built and used NASA’s Cosmic Background Explorer (COBE) satellite, which Mather played a key role in making a reality in 1989. Researchers used the images of the primordial light, called the cosmic microwave background radiation, to confirm that the universe burst forth from a very hot and dense early state—a process commonly called the big bang. In 2006, Mather shared the Nobel Prize in physics for the work.
After COBE, Mather became a senior project scientist on NASA’s James Webb Space Telescope (JWST) in 1995. He worked for more than a quarter of a century to make the state-of-the-art telescope a reality before it finally launched in December of 2021.
But Mather wasn’t ready to end his career when the JWST became a reality. The launch of the JWST heralded a new chapter for him, in which he splits his time between sharing the JWST’s results with the world and developing new projects to uncover more of the universe’s mysteries.
JWST: A Long-Haul Effort
Launching the JWST was the start of its story as a tool for scientific discovery, but it was also the conclusion of a massive effort by Mather and many others. Mather had been part of the JWST team since the beginning. He worked on the original proposal in 1995 and proceeded to spend the next decades helping engineers design the telescope; coordinating with team members from Europe, Canada and across the US; and generally working to keep the project on track.
The years of effort produced an array of mirrors designed to unfold into a 21-foot-wide final configuration. The delicate mirrors and necessary equipment were placed on top of a rocket, and Mather and his colleagues put their faith into their years of preparation.
As the final seconds to the launch counted down, Mather watched the fate of the mission play out from his sofa at home. The JWST team had a busy schedule planned for months after the launch, and they didn’t want cases of COVID-19, or anything else, disrupting their carefully laid plans.
“Nobody was allowed to go anywhere, to take any chances with catching that bug,” Mather said. “Because we needed them to be alive and ready to work at any moment.”
The launch went off without a hitch, but that didn’t mean the team could breathe a sigh of relief. It was still possible the telescope could fail to produce any images. The telescope had to travel almost a million miles to its final orbit, successfully unfold itself and calibrate multiple components before researchers could tell if it was actually working.
Its predecessor, the Hubble Space Telescope, couldn’t take images in focus when it was first deployed because of a slightly misshapen mirror. A similar issue would be much more devastating for the JWST because its final destination was almost 3,000 times farther from Earth—about four times farther than the moon. So any repair visit would be impractical and unlikely to be attempted.
“The sort of moment of truth was the first image we got which showed focus,” Mather said. “About 40 people or so were assembled in the control rooms at the Space Telescope Science Institute. They all got to look at this wonderful image at the same time, and it was covered with galaxies. So we knew that not only had we done a great engineering job but there were things to study everywhere.”
JWST: Reaping the Benefits
The JWST has so much to study because it can see much farther than its predecessors. When light travels far enough, the waves making it up get stretched out and becomes harder to see (the universe itself is expanding which stretches out light along with it). As planned, detecting ancient light has revealed objects from the earliest periods of the universe that scientists have ever seen (after the messy period that produced the microwave background radiation). With this new window into the past, scientists have confirmed theories, such as how galaxies take time to spin themselves into shape, as well as uncovered new mysteries, like spotting unexpectedly bright galaxies in the early universe.
Besides capturing stretched-out light, the JWST has another tool for observing the farthest reaches of space. Like a photographer pulling out a high-powered lens to capture a distant subject, the JWST has tools for zooming in on distant corners of the universe. NASA didn’t have to make them; the JWST takes advantage of natural lenses that are formed by the gravity of many galaxies that are clustered together. The collective gravity warps space and makes a gravitational lens that directs light along a curved path similar to how a glass lens bends light.
A gravitational lens took center stage in the first JWST image released to the public and revealed the glittery details of one of Mather’s favorite galaxies to talk about—the “Sparkler Galaxy.” The signature sparkles are dense clusters of stars that are important for understanding the initial formation of a galaxy.
The JWST isn’t only revealing the distant universe; it is also giving us better snapshots of our own neighborhood. The specialized cameras on the JWST have been used to detect light carrying the signatures of interactions with specific molecules. Researchers have used this to study other planets and moons in our solar system.
“I was ignorant about the solar system, and I am really surprised and pleased to see that we're able to map the presence of molecules on the satellites in our solar system,” Mather said. “We see that on Titan, which is a satellite of Saturn, we're able to make a map of where different molecules are, and that's interesting, because it's the only satellite in the solar system that has an atmosphere of its own to speak of.”
The data from inside and outside our solar system keep pouring in, and researchers continue to propose new ways the JWST can advance science. After the team was sure the project was running smoothly, Mather handed over his position as the JWST’s senior project scientist to Jane Rigby in 2023. But that doesn’t mean he hasn’t been keeping an eye on the mission.
“Following the conclusion of my work on the James Webb Space Telescope, I follow along the science that's being produced, and I give a lot of public talks about that,” Mather said. “I really enjoy doing that because people want to know what we found, and they are still thrilled with the brilliant engineering.”
Orbiting Starshades: Going the Distance to Get the Shot
While the JWST results continue to excite Mather, he wanted to return to his roots problem-solving and developing projects to uncover new pieces of the heavens.
“I enjoy the creative part at the beginning, and after you get past that, then I'm a little nervous and impatient, and my job was basically running a lot of meetings for a long time, and that's not as much fun as thinking of something new to work on, for me,” Mather said. “It's definitely important to do, but it's just a different thing.”
The new project that has caught Mather’s interest is getting the perfect lighting to photograph planets in other solar systems—exoplanets. To do so, he wants to put a satellite, called a starshade, into orbit. A starshade would obstruct the light of a star before it reaches a telescope, but they need to be outside the atmosphere to work. One could be paired with a telescope that is also in space, like the Hubble Space Telescope, but Mather thinks they have the greatest potential when partnered with the massive telescopes we build on the ground.
Obstructing the light from a star should allow the telescope to pick up the much dimmer light reflected by a planet orbiting it. It’s like watching a plane flying in the same part of the sky as the sun: To avoid being blinded, you raise your hand to block out the sun.
By blocking a star’s light, a telescope can not only spot nearby planets but also detect the signature of molecules, like oxygen and water, that the light interacted with when it passed through a planet’s atmosphere. Such measurements would dramatically upgrade our ability to discover and study many more planets throughout the universe.
Current methods of identifying exoplanets generally rely on observing a planet’s gravitational influence on a star or detecting it pass between its star and us (we notice a slight dimming of the star, rather than actually observing the planet). These approaches let us discover planets around stars that are much smaller than our sun or detect large planets—similar to the gas giants in our solar system—that are near their star. But the available techniques leave us effectively blind to the planets most like Earth.
However, before they can hunt for Earth-like exoplanets, researchers must solve the unique challenges of getting a working starshade in orbit. A planet can be billions of times dimmer than the star, and because of the vast distances between us and other solar systems, planets and their sun are almost indistinguishable specks. To get the right lighting, scientists must place the starshade in front of the star without accidentally covering the planet right next to it.
They must also account for the fact that light sometimes deviates from a straight-line path. Light travelling from one medium, like air to water or thin air to dense air, shifts its direction (stars “twinkle” because of these distortions occurring as its light travels through Earth’s atmosphere). Light also changes its direction by bending around the edges of objects—including the edges of the starshade.
Combining all the known constraints gave Mather and his colleagues strict requirements for designing a starshade to work with a telescope on the ground.
“It needs to be a pointy sunflower, 100 meters in diameter, located at least 175,000 kilometers away from us in orbit around the Earth,” Mather said. “So that's huge. And the normal ways we would build something like that would make it also very heavy.”
The petals of the massive flower shape that researchers have settled on ensure the stray light deflected around them doesn’t get sent toward the center of a telescope. But the potential bulk of the structure has a cost; heavy satellites are expensive to launch and difficult to maneuver into position. So now Mather and his colleagues are brainstorming ways to make the starshade as light as possible.
One of the approaches they are considering is making it inflatable: Cut a sheet into the right shape and make a balloon frame to support it. But the approach leaves them concerned about the whole thing popping. While space is mostly empty, there are small objects—micrometeorites—zipping around, and over time collisions happen. So Mather and his colleagues also need to make the starshade durable.
A key idea they are pursuing is sending up multiple layers of sheets so that when a micrometeorite slams through them, the different layers can still block out most of a star’s light. It’s only an issue if the star’s light happens to follow the exact same trajectory as one of the micrometeorites. However, the team still needs a way to reinforce the inflatable framework to survive collisions.
The team is considering building the frame using resins or other materials that could undergo a chemical transformation into a sturdy structure after being deployed into shape. Another idea they are playing with is to deflate the starshade when it is not in use so that it is a smaller target and will get hit less often.
While developing the starshade, Mather is also pursuing related projects, like putting a stable standard light source—an artificial star—in orbit to aid ground-based telescopes. Having a steady light at a known brightness in the sky can help astronomers study stars. Astronomers don’t always know the actual brightness of objects they see through telescopes, and analysis is complicated because the atmosphere distorts the light before it reaches the telescope. Having a steady light above the atmosphere gives astronomers a point of comparison for determining the true brightness of what they observe. More importantly, it can also help them reverse engineer the distortions of the atmosphere and piece together the original image.
This technique will support future experiments using orbiting starshades since any light from the planet that reaches the ground will be distorted and require correction. Mather is part of a project led by George Mason University researchers that plans to put an artificial star into orbit in 2029.
Mather is also throwing his support behind other projects that are further into their development, like the Black Hole Explorer, which aims to observe light that has orbited black holes. While Mather’s various projects generally look into the far reaches of space, he’s still invested in learning about our home. Both Mather’s past and upcoming work explore our origins as they open up the wider universe to us.
“We actually said we were going to try to discover our own history by looking at the history of other places,” Mather said. “So what's the history of our own galaxy? Well, you can't really tell, but you can look at the formation of galaxies. You can look back in time by looking at things that are far away. So we're getting a photo album of ourselves by looking at our cousins way out there and seeing what were they like when they were young.”
Written by Bailey Bedford
