John Mather on James Webb, Exoplanets & Cosmic Discovery

Susan Wise: Welcome to Star Launch Pod, Space Technology and Research Sciences, brought to you by starsciences.org, where we connect, collaborate, and accelerate. I’m your host, Susan Wise, and I’m thrilled to have with us today John Mather, Senior Astrophysicist at NASA Goddard Space Flight Center, cosmologist, Nobel Prize winner in Physics, and Senior Project Scientist for the James Webb Telescope.
John Mather, welcome to our show—welcome to Launch Pod.

John Mather: Thank you. I’m glad to be here with you all.

Susan Wise: It’s truly an honor. I’m actually a little nervous, I don’t mind saying, because I watched Cosmic Dawn the other day. What a great documentary—it taught me so much about the Webb Telescope and everything that went into it. It’s been in the news lately with some exciting discoveries. What are you currently working on to help further the space industry?

John Mather: My current idea is called a hybrid observatory for Earth-like exoplanets. The idea is that we have large telescopes being built on the ground, and if we could block the starlight coming in, we would be able to see the small planets hovering nearby. People usually think we need a space telescope for this, but I believe we can also use ground-based telescopes. At least three giant telescopes are in progress—two U.S.-led and one European-led in Chile. They are far larger than anything we can launch into space right now. If we can harness their power with a star shade, we could capture images of other Earth-like planets—just small dots, not continents or oceans, but planets orbiting other stars.

Susan Wise: Is this still in the dream stage, or has it moved forward?

John Mather: It’s still in the dream stage in the sense that we don’t yet have a finalized design. What’s required is pretty amazing. We need something called a star shade, which looks like a giant sunflower about 100 meters in diameter—the length of a football field. It must be ultra-light so we can maneuver it in space with rocket engines, positioning it between the star and telescope. If we succeed, we could capture pictures of entire solar systems.

Susan Wise: Wow, that would be amazing. Would the star shade be launched in pieces and assembled in space while the telescope is on the ground?

John Mather: The telescopes are already being built on the ground, and yes, the star shade would be unfolded in space. We’re still exploring designs: inflatables, modular cubes assembled by robots, or mechanical structures that unfold themselves. We haven’t settled on the best option yet.

Susan Wise: This is exciting because the James Webb Telescope was groundbreaking, but you’re talking about taking things even further.

John Mather: That’s our hope. Astronomers have long wanted a telescope designed specifically to find Earth-like planets. Such a mission would be as complex, expensive, and ambitious as Webb. But with the star shade, we might not need to build a new telescope—just the shade. Of course, it’s easier said than done, but we think it’s achievable.

Susan Wise: It all starts with an idea. What has been one of your biggest “aha” moments?

John Mather: There have been several. The first led to the Nobel Prize. In graduate school, many of us realized that with a satellite we could measure the cosmic microwave background radiation—the leftover heat from the early universe—much better than from the ground. My thesis project involved measuring its color to prove it was truly cosmic. The COBE satellite was launched 15 years later, and when we saw the data confirming the prediction, it was an incredible moment. It proved the radiation really is from the early universe.

Another “aha” was realizing we needed to map the background radiation to see if it was uniform. We proposed that in 1974, right after I finished graduate school. We were young and unsure, but with NASA Goddard’s engineering support, we built it. When we discovered the hot and cold spots—the pink and blue blobs—you see in sky maps, it was a breakthrough no one had expected at the start.

Susan Wise: I imagine you’ve faced challenges along the way. Is there one that stands out?

John Mather: Many challenges are team challenges. With COBE, the biggest was the Challenger disaster. We had planned to launch on the Shuttle, but after the accident we had to redesign the satellite for a Delta rocket. That was a huge change, but the team succeeded.

There were also personal challenges. Twice I discovered errors in my own calculations that others were relying on. The lesson: never trust the boss—not even if you are the boss. Always have someone check your work. Teamwork and verification are essential.

With the James Webb Telescope, the biggest challenge was running out of money. Congress and Senator Mikulski asked for an independent review, which concluded the project was sound but underfunded. We received additional funding and time, which allowed us to finish despite COVID delays.

Susan Wise: So the lesson is to ask for more than you think you need.

John Mather: Exactly. James Webb, NASA’s second administrator and the telescope’s namesake, once doubled his budget request in a taxi on the way to the White House. If he hadn’t, the Apollo program could have failed. You’re never smart enough to predict everything in advance—so ask for more resources.

Susan Wise: What’s the most exciting discovery from the James Webb Telescope so far?

John Mather: Several things. One is a category of objects we call “little red dots,” seen in the first billion years of the universe. They may be compact galaxies or galaxies with black holes, but no one knows yet. This could be a clue to how black holes formed.

Another is studying exoplanets. We can’t yet study Earth-sized ones well, but we’ve examined large planets close to their stars, analyzing their atmospheres, chemistry, and temperature. It’s not Earth 2.0 yet, but there are many candidates. I’d be shocked if no Earth-like planets exist, though our solar system’s exact structure may be rare.

Susan Wise: What advice would you share with our listeners?

John Mather: If your work is important to the world, you’ll find a way to do it—but don’t do it alone. Ask for help. Declaring your project worthy of help makes others willing to join. Build a team. Life is a team sport.

Susan Wise: Do you have a passion project you’d like to share?

John Mather: Yes—the orbiting star shade. Few people took it seriously at first, but I think it could work. It could revolutionize how we study exoplanets and improve ground-based telescopes through hybrid observatories.

Susan Wise: I cannot wait to see the first pictures from these future projects.

John Mather: Thank you. We have high hopes and many possibilities.

Susan Wise: Thank you so much for joining us on Launch Pod. We deeply appreciate you, John Mather—Senior Astrophysicist at NASA Goddard Space Flight Center, cosmologist, Nobel Prize winner in Physics, and Senior Project Scientist for the James Webb Telescope. Be sure to join starsciences.org to receive a free one-year membership by entering promo code FRIENDS321. If you enjoyed this episode, leave us a review and subscribe. Until next time, keep looking up. Thank you, John.