In Scientific Controversies, hosted by our own Janna Levin, we tackle complex, conceptual, occasionally amorphous topics like animal consciousness and string theory. These rich, hour-long conversations take place in person at Pioneer Works, and feature big thinkers exchanging on big questions. To watch is a feast. “5 Takeaways” is a snack, an amuse-bouche for the mind. Because comprehension sometimes demands—or, at the very least, appreciates—distillation, and the internet loves a listicle. Below, for the benefit of lay science enthusiasts, leading astronomy journalist Stuart Clark serves up key takeaways from a conversation on the James Webb Space Telescope between Wendy Freedman and John Mather, clips of which we've sprinkled throughout.

What’s with the buzz about this thing called JWST?

JWST, or the James Webb Space Telescope, is the largest telescope we’ve ever sent into space. A joint effort between NASA, the European Space Agency (ESA), and the Canadian Space Agency, the telescope is so big, it had to be folded origami-style into the nose cone of ESA’s Ariane 5 rocket. Weeks after its launch on Christmas Day, 2021, NASA engineers and enthusiasts everywhere held their collective breath as the JWST successfully completed a series of maneuvers, with numerous single points of failure, each of which could have doomed the mission. Soon after separating from the rocket, it deployed its solar array and sped towards a special place in space called the second Lagrange Point (L2), almost a million miles from Earth. During the first week of its journey, JWST opened its sunshield, a tennis court-sized barrier that shelters the telescope from the heat of the Earth and the Sun. Made of five layers of polymer material, each about one thousandth of an inch thick each, the sunshield had to unfold perfectly, with no snags or tears. And it did. Its purpose is to create a temperature difference of about 570 degrees Fahrenheit between its sunward side and the telescope’s optics and instruments, which work in its shade. The JWST took a month to reach L2, at which point it had deployed its telescope tower, and the primary and secondary mirrors, all while powering up its instruments. At 6.5 meters across, the JWST’s primary mirror is now the largest telescope mirror in space.

What makes the mirror so special?

It has 6.25 times the light collecting area of its predecessor, the 2.4-meter mirror of the Hubble Space Telescope (HST). Also, unlike the HST’s monolithic mirror, the JWST’s mirror has eighteen hexagonal elements, each made of ultra-light and stiff beryllium. JWST unfolded its mirror as it flew to L2, and once it arrived, NASA engineers aligned these hexagonal elements to a precision of about ten-thousandths of the thickness of human hair. This allows them to act as a single, large mirror. The mirror’s size, and the chill afforded by its sunshield, means that the JWST can observe light at infrared wavelengths. Compared to the HST, which sees mainly in optical wavelengths, JWST can detect cooler objects. Since infrared light can go through dust, much like X-rays through bodies, the JWST can peer through dust clouds, which often harbor newly-forming planets and stars. It might even see some of the earliest objects that formed in our universe, because the cosmos’ expansion would have stretched the light from these objects into JWST’s infrared range.

Why should astronomers study these earliest objects?

Scientific curiosity, for one. JWST is designed to look for the first objects that formed a few 100 million years after the cosmic microwave background (CMB) radiation, the big bang’s fossil radiation, flooded the universe. Were these objects stars or galaxies or black holes? JWST should see the first glimmers of such objects and thus help answer an astrophysical mystery: how did the supermassive black holes that we see today at the center of most galaxies get so big so quickly? Did they start forming soon after the big bang, or did they arise from processes we don’t yet understand? The JWST will look for the potential seeds of these supermassive black holes. Finding them could give astrophysicists further insights into the formation of galaxies, in particular, and the general evolution of structure in the universe.

What else can such observations tell us about the universe?

The JWST will also help solve another mystery that’s been exquisitely set up by the Hubble Space Telescope. Before the HST was launched in 1990, astronomers were struggling to put bounds on something called H0 (read that as “H-naught”), the Hubble constant—a single number that tells us how fast the universe is expanding today. Calculating this number requires precise measurements of the distances to objects such as Cepheid variable stars and type IA supernovae. Before HST, estimates of H0 varied wildly, landing anywhere between 50 and 100 kilometers per second per megaparsec. The HST’s observations have helped astronomers pin this number down to 73.04 ± 1.04. But an entirely different method, using precise observations of the cosmic microwave background, gives H0 to be 67.49 ± 0.53. Either one of these estimates is wrong or we are missing something crucial in our understanding of the universe and its evolution. The JWST will help resolve this debate by studying so-called red-giant-branch stars, which are stars at the end of their lives that have expanded and cooled somewhat. JWST will accurately measure the luminosity of such stars, which will help astronomers calculate the distance to galaxies that host these red giants and make a more precise estimate of H0.

Is there anything close by that the JWST will set its sights on?

Yes, among its targets are exoplanets in our own galaxy. The JWST has the instruments to analyze the spectrum of starlight that filters through the atmosphere of planets orbiting other host stars. The spectrum can tell astronomers about the chemical elements in the planet’s atmosphere: is there water, or carbon, or oxygen, or methane, for example? Already, the JWST has found carbon dioxide and sulfur dioxide in the atmosphere of WASP-39b, a Saturn-sized planet orbiting a star about 700 light years from Earth. JWST will soon study a system of seven rocky, Earth-sized planets orbiting TRAPPIST-1, a red dwarf star that’s a mere 40 light years away. A number of these planets could be potentially habitable. So even as we marvel at JWST’s ability to look deep into the distant past, its most momentous discoveries may come from closer to home. ♦