Astronomers using NASA’s James Webb Space Telescope (JWST) have discovered water, methane, ammonia, and carbon dioxide in the atmosphere of a gas giant planet called HATS-6 b, located about 500 light-years away. This planet, roughly the size of Jupiter, orbits an M dwarf—a small, cool, reddish star—every three days. The findings, published in the Astronomical Journal, challenge existing theories about how giant planets form and evolve, especially around small stars. HATS-6 b is part of a rare group of planets known as "giant exoplanets," which are much larger than Earth but not as massive as the Sun. These planets are typically found around stars similar to our Sun, but HATS-6 b orbits an M dwarf, a star much smaller and cooler than our Sun. According to the study's lead author, Giannina Guzmán Caloca, an astronomy Ph.D. candidate at the University of Maryland, the planet's size should not be possible around such a small star. "Smaller stars have smaller disks of gas and dust from which planets form," she explained. "So, the fact that HATS-6 b exists is really interesting because it shouldn't be possible with what we know." HATS-6 b is one of seven planets being studied in a JWST program called "Giant Exoplanets around M-dwarf Stars" (GEMS), which aims to compare these unusual planets with more familiar giant planets around stars like our Sun. Guzmán Caloca noted that each of these planets challenges current theories of planet formation. By analyzing their atmospheres, scientists can determine whether they formed in a similar way to the "hot Jupiters" found around sun-like stars or if different processes are at play. The team used a technique called transmission spectroscopy to study HATS-6 b’s atmosphere. This method involves observing how starlight filters through the planet's atmosphere as it passes in front of its star. The analysis revealed four molecules—water, methane, ammonia, and carbon dioxide—in the planet’s atmosphere. The presence of ammonia, in particular, is significant because it has rarely been detected in the atmospheres of exoplanets. "Carbon, hydrogen, and oxygen have been found before, but ammonia is something almost never detected," Guzmán Caloca said. "It's an entirely new molecule to think about." The discovery also raises questions about the planet’s temperature. While HATS-6 b is commonly estimated to be around 800 degrees Fahrenheit (425 degrees Celsius), this is based on assumptions about how the planet absorbs and distributes heat. Earlier studies suggested a much lower temperature, closer to 250 degrees Fahrenheit (120 degrees Celsius), which seems too cool for a planet so close to its star. Guzmán Caloca speculated that clouds or haze might be reflecting a significant amount of starlight, preventing the planet from warming up as expected. This idea is similar to how Venus is shrouded in thick clouds that trap heat. These findings have broader implications for understanding exoplanets. Temperature is a key factor in determining the composition of a planet’s atmosphere, and a discrepancy as large as this could affect how scientists interpret atmospheric data for planets around small, active stars. Guzmán Caloca and her team are continuing to study HATS-6 b with longer-wavelength observations to uncover more clues. As astronomers have discovered over 6,000 exoplanets, many of which are unlike any in our solar system, analyzing their atmospheres can help determine if other solar systems formed in ways similar to our own. "What is our context? And how rare or how common are we?" Guzmán Caloca asked. "This is one planet out of thousands, but the way I like to think about it is that Earth is also one planet out of thousands and yet it holds everything that ever lived here."