 |
| An artist’s concept depicts Centaur 29P/Schwassmann-Wachmann 1’s outgassing activity, highlighting new observations from NASA’s James Webb Space Telescope that revealed additional jets of gas, expanding on prior findings of a jet directed toward Earth. |
Inspired by the half-human, half-horse creatures of Ancient Greek mythology, the field of astronomy has its own kind of centaurs: distant objects that orbit the Sun between Jupiter and Neptune. Recent observations from NASA’s James Webb Space Telescope have mapped the gases emitted by one of these centaurs, revealing a diverse composition and offering new insights into the formation and evolution of our solar system.
Centaurs are former trans-Neptunian objects that have been nudged inside Neptune’s orbit by the gravitational influences of the planets over the last few million years, and they may eventually evolve into short-period comets. These objects are “hybrid” in nature, existing in a transitional phase of their orbital evolution. Many exhibit characteristics of both trans-Neptunian objects, originating from the cold Kuiper Belt, and short-period comets, which undergo significant changes from repeated close encounters with the Sun.
Since these small icy bodies are in a transitional orbital phase, they have been the focus of numerous studies aimed at understanding their composition, the mechanisms behind their outgassing—specifically the loss of subsurface ices—and their role as a link between primordial icy bodies in the outer solar system and evolved comets.
Recently, a team of scientists utilized Webb’s NIRSpec (Near-Infrared Spectrograph) to gather data on Centaur 29P/Schwassmann-Wachmann 1, known for its highly active and quasi-periodic outbursts that occur every six to eight weeks, making it one of the most dynamic objects in the outer solar system. They identified a new jet of carbon monoxide (CO) and previously unseen jets of carbon dioxide (CO2), providing fresh insights into the centaur’s nucleus.
Centaurs can be considered some of the leftovers from our planetary system’s formation. Stored at very cold temperatures, they preserve information about volatiles from the early solar system,explained Sara Faggi of NASA’s Goddard Space Flight Center and American University, lead author of the study. Webb opened the door to an impressive resolution and sensitivity—we were thrilled when we first saw the data; we had never encountered anything like this.
Webb and the Jets.
The distant orbits and faintness of centaurs have historically limited detailed observations. Prior radio wavelength data on Centaur 29P indicated a jet primarily directed toward the Sun (and Earth) composed of carbon monoxide (CO). Using its large mirror and infrared capabilities, the James Webb Space Telescope not only detected this face-on jet but also searched for other chemicals, including water (H2O) and carbon dioxide (CO2), the latter being a major carbon storage form in the solar system. Notably, no water vapor was found in 29P’s atmosphere, possibly due to the extremely cold temperatures of this body.
Webb’s unique imaging and spectral data uncovered unprecedented features: two jets of CO2 emanating in the north and south directions, along with another CO jet directed northward. This marked the first definitive detection of CO2 in Centaur 29P.
IFU Graphic.
 |
| An artist’s concept illustrates Centaur 29P/Schwassmann-Wachmann 1’s outgassing activity, highlighting new insights from NASA’s James Webb Space Telescope, which revealed the front jet’s composition and identified three additional jets of gas from the surface. |
Based on the data collected by Webb, the team developed a 3D model of the jets to analyze their orientation and origin. Their modeling revealed that the jets originated from different regions of the centaur’s nucleus, despite Webb’s inability to resolve the nucleus itself. The angles of the jets suggest that the nucleus might be an aggregate of distinct objects with varying compositions; however, other scenarios remain possible and cannot be ruled out at this stage.
The dramatic differences in the abundance of CO and CO2 across Centaur 29P’s surface suggest that it may be composed of several pieces,” said Geronimo Villanueva, co-author of the study at NASA Goddard. “It’s possible that two distinct bodies coalesced to form this centaur, representing a mixture of objects that followed separate formation pathways. This challenges our understanding of how primordial objects are created and stored in the Kuiper Belt.
The reasons behind Centaur 29P’s bursts in brightness and the mechanisms driving its outgassing activity via the CO and CO2 jets remain key areas of inquiry needing further exploration.Unlike comets, which often have jets driven by water outgassing, centaurs are too cold for water ice to sublimate, resulting in fundamentally different outgassing processes.
“We only had time to examine this object once, like a snapshot in time,” noted Adam McKay, a co-author of the study at Appalachian State University. “I’d like to revisit Centaur 29P over a longer duration. Do the jets maintain their orientation? Is there a carbon monoxide jet that activates at a different point in its rotation? Observing these jets over time would provide valuable insights into what drives these outbursts.”
The team is optimistic that by enhancing their understanding of Centaur 29P, they can apply similar techniques to other centaurs. This broader knowledge could deepen our understanding of the formation and evolution of our solar system.These findings have been published in Nature, based on observations from General Observer program 2416.
