Why JWST Found Carbon Dioxide On An Exoplanet
The light hitting one of humanity's most powerful telescopes right now left its home planet 700 years ago, before Columbus set sail, back when knights still rode into battle. That planet sits about 4.12 quadrillion miles from Earth, a gas giant so hot its air roasts at around 1,600 degrees Fahrenheit. And when the James Webb Space Telescope caught that ancient light, it found something no telescope had ever detected in the atmosphere of an alien world: carbon dioxide, a gas that on Earth signals the breath of living things.
The Telescope and Its Namesake
The James Webb Space Telescope (JWST), also known as Webb, is named after James E. Webb (October 7, 1906 - March 27, 1992). Webb was the NASA administrator from 1961 to 1968 during the Apollo, Gemini, and Mercury programs. He was known for promoting racial integration at NASA and increasing participation, hiring, and promotion of Black scientists.
As innovative as its namesake, the James Webb Space Telescope is an observatory that extends the Hubble Space Telescope's discovery capabilities. Launched on Dec. 25, 2021, the JWST was built by an international collaboration of NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The mission of the JWST is to study space and how the universe evolved from the Big Bang, the beginning of the Universe. The telescope studies the formation of stars, planets, exoplanets, and other celestial entities.
How the JWST "Sees" Distant Worlds
The JWST doesn't take photographs the way a phone camera does. To learn what a planet 700 light-years away is made of, it splits incoming light apart. Its primary mirror is a gold-coated giant built from 18 separate segments that unfolded like a flower once the telescope reached space, giving it a huge surface to catch the faint glow of far-off worlds.
The real magic happens with two instruments. The NIRSpec (Near Infrared Spectrograph) can watch up to 100 objects at once, breaking their light into a rainbow of colors. Each gas leaves its own fingerprint in that rainbow, so the pattern reveals exactly which chemicals float in a planet's atmosphere. The NIRCam (Near Infrared Camera) handles the imaging, and one of its tricks is crucial for planet-hunting: it can block the blinding glare of a star, the way you might raise a hand against the Sun, so that a dim planet next to it finally becomes visible. Together, these tools let the JWST identify the invisible gases surrounding a world it will never physically reach.
Keeping the Telescope Colder Than Deep Space
To detect heat signatures from across the galaxy, the JWST has to be colder than almost anything around it. A sunshield the size of a tennis court blocks the Sun's heat by more than a million times, and a special cooler chills its most sensitive detectors to about 7 kelvins, roughly minus 447 degrees Fahrenheit. That's only a few degrees above absolute zero, the coldest temperature physically possible. Any warmer, and the telescope's own heat would drown out the faint infrared light it's straining to see.
WASP-39b: A Furnace in the Sky
WASP-39 b is a gas giant, a planet with no solid ground to stand on, just swirling layers of hydrogen and helium wrapped around a hidden core. It circles a yellow star much like our own Sun, but it orbits so close that its atmosphere blisters at around 1,600 degrees Fahrenheit, hot enough to melt aluminum. Even its "cooler" parent star burns at 5,330 kelvins, more than 9,000 degrees Fahrenheit. This is not a world where anything could survive; it's a scorched, airless furnace. And yet it became one of the most important planets in the history of astronomy.
Why the JWST Found Carbon Dioxide
Reaching WASP-39 b in person is essentially impossible. Even traveling at the speed of light, the fastest speed in the universe, the trip would take 700 years. With today's spacecraft, it would take far longer, tens of thousands of years, meaning generations of humans would be born and die before anyone arrived. That impossible distance is exactly why the JWST exists: to "visit" alien worlds without ever leaving Earth's neighborhood.
What the telescope found was a landmark. As starlight filtered through WASP-39 b's atmosphere, the JWST detected both water vapor and, for the first time ever on a planet beyond our solar system, carbon dioxide. On Earth, carbon dioxide pours out of living, breathing organisms, so finding it around distant worlds is one clue scientists watch for when hunting signs of life. WASP-39 b itself is far too hot to host anything living. But proving the JWST could sniff out this gas across 4.12 quadrillion miles changed what astronomers believe is possible, opening the door to searching cooler, gentler worlds for the true chemical signatures of life.
The Future of JWST
Despite its amazing discoveries, the JWST cannot go on its mission forever. The telescope is fueled by a propellant that will eventually run dry. Initially, NASA thought the JWST would be operational for 5 to 10 years, but it has lasted longer thanks to the precision of the Ariane 5 rocket that launched it, which saved fuel by placing the telescope almost perfectly on course. When the last of the fuel burns away, pressure from the Sun will slowly shove the JWST out of its orbit. It will drift into a wider, silent path around the Sun, becoming a solar relic in a hushed graveyard of space debris. With its predicted end around 2040, there are no rescue missions planned and no spacecraft on Earth capable of reaching it. Watching in awe at the images it sends home while it still can may be the only memorial it will ever get.
