Free Astronomy Magazine January-February 2025

13 JANUARY-FEBRUARY 2025 ASTRO PUBLISHING Flight Center in Greenbelt, Mary- land, and American University in Washington, DC, lead author of the study. “Webb really opened the door to a resolution and sensitivity that was impressive to us — when we saw the data for the first time, we were excited. We had never seen anything like this.” Centaurs’ distant orbits and conse- quent faintness have inhibited de- tailed observations in the past. Data from prior radio wavelength obser- vations of Centaur 29P showed a jet pointed generally toward the Sun (and Earth) composed of CO. Webb detected this face-on jet and, thanks to its large mirror and in- frared capabilities, also sensitively searched for many other chemicals, including water (H 2 O) and CO 2 . The latter is one of the main forms in which carbon is stored across the solar system. No clear indication of water vapor was detected in the at- mosphere of 29P, which could be re- lated to the extremely cold temper- atures present in this body. The telescope’s unique imaging and spectral data revealed never-before- seen features: two jets of CO 2 ema- nating in the north and south direc- tions, and another jet of CO point- ing toward the north. This was the first definitive detection of CO 2 in Centaur 29P. Based on the data gathered by Webb, the team created a 3D model of the jets to understand their ori- entation and origin. They found through their modeling efforts that the jets were emitted from different regions on the centaur’s nucleus, even though the nucleus itself can- not be resolved by Webb. The jets’ angles suggest the possibility that the nucleus may be an aggregate of distinct objects with different com- positions; however, other scenarios can’t yet be excluded. “The fact that Centaur 29P has such dramatic differences in the abun- T his is an animation portraying the outgassing activity of Cen- taur 29P/Schwassmann-Wachmann 1 based on data gathered by NASA’s James Webb Space Telescope’s NIR- Spec (Near-Infrared Spectrograph) instrument. Centaur 29P is one of the most active objects in the outer solar system, undergoing quasi-pe- riodic outbursts in brightness. The video begins by zooming in for a closer view of an artist’s concept of Centaur 29P. The scene is over- laid with graphics that help define the four different jets of gas before the centaur is rotated so the object can be examined from different angles. [NASA, ESA, CSA, Leah Hus- tak (STScI)] dance of CO and CO 2 across its sur- face suggests that 29P may be made of several pieces,” said Geronimo Villanueva, co-author of the study at NASA Goddard. “Maybe two pieces coalesced together and made this centaur, which is a mixture be- tween very different bodies that un- derwent separate formation path- ways. It challenges our ideas about how primordial objects are created and stored in the Kuiper Belt.” The reasons for Centaur 29P’s bursts in brightness, and the mechanisms behind its outgassing activity through the CO and CO 2 jets, con- tinue to be two major areas of in- terest that require further inves- tigation. In the case of comets, sci- entists know that their jets are often driven by the outgassing of water. However, because of the cen- taurs’ location, they are too cold for water ice to sublimate, meaning that the nature of their outgassing activity differs from comets. “We only had time to look at this object once, like a snapshot in time,” said Adam McKay, a co-au- thor of the study at Appalachian State University in Boone, North Carolina. “I’d like to go back and look at Centaur 29P over a much longer period of time. Do the jets always have that orientation? Is there perhaps another carbon monoxide jet that turns on at a dif- ferent point in the rotation period? Looking at these jets over time would give us much better insights into what is driving these out- bursts.” The team is hopeful that as they increase their understanding of Centaur 29P, they can apply the same techniques to other centaurs. By improving the astronomical com- munity’s collective knowledge of centaurs, we can simultaneously bet- ter our understanding on the for- mation and evolution of our solar system. !