Astronomers, utilizing NASA’s James Webb Space Telescope, have achieved a groundbreaking milestone by observing water and other molecules within the intensely irradiated inner regions of a disk involved in the formation of rocky planets. This extraordinary feat, part of the eXtreme Ultraviolet Environments (XUE) James Webb Space Telescope program, sheds light on the conditions conducive to the formation of terrestrial planets in environments previously considered extreme.
The focus on characterizing planet-forming disks within massive star-forming regions unveils insights into the environments where most planetary systems likely originated. These findings offer a broader perspective on the potential range of conditions influencing terrestrial planet formation, providing essential knowledge for understanding the diversity of exoplanets in various environments across our galaxy.
The eXtreme Ultraviolet Environments (XUE) program focuses on examining 15 disks within three regions of the Lobster Nebula (NGC 6357), situated approximately 5,500 light-years away in the Scorpius constellation. As one of the youngest and closest massive star-forming complexes, the Lobster Nebula harbors some of the galaxy’s most massive stars, emitting substantial ultraviolet (UV) radiation. The intense UV radiation from these massive stars can disperse gas, potentially shortening the expected lifetime of protoplanetary disks to as little as a million years.
With the unique capabilities of the James Webb Space Telescope, astronomers can now investigate the impact of UV radiation on the inner regions of rocky-planet forming disks around stars, including those akin to our Sun. María Claudia Ramírez-Tannus from the Max Planck Institute for Astronomy in Germany, the team lead, emphasizes that Webb’s spatial resolution and sensitivity make it the sole telescope capable of studying these disks in massive star-forming regions.
The astronomers involved in the eXtreme Ultraviolet Environments (XUE) program are dedicated to characterizing the physical attributes and chemical makeup of the rocky-planet-forming regions within the disks of the Lobster Nebula, employing the Medium Resolution Spectrometer on the James Webb Space Telescope’s Mid-Infrared Instrument (MIRI). The initial focus of their efforts centers on XUE 1, a protoplanetary disk situated within the star cluster Pismis 24.
Team member Arjan Bik from Stockholm University underscores the critical role of MIRI’s wavelength range and spectral resolution, which uniquely enable the examination of the molecular inventory and physical conditions within the warm gas and dust environments where rocky planets take shape.
XUE 1 shows data from a protoplanetary disk.
The spectral data from the protoplanetary disk, XUE 1, within the star cluster Pismis 24, provides intriguing insights. Highlighted in blue, the inner disk of XUE 1 exhibits distinct signatures of water, alongside acetylene (C2H2) in green, hydrogen cyanide (HCN) in brown, and carbon dioxide (CO2) in red. Notably, some emissions are weaker than predicted by models, hinting at a potentially smaller outer disk radius.
Positioned in proximity to several massive stars in NGC 6357, XUE 1 has likely experienced continual exposure to high levels of ultraviolet radiation. Despite this extreme environment, the research team detected a diverse range of molecules—key building blocks for the formation of rocky planets. This finding challenges previous assumptions about the limits of planetary formation in such intense radiation environments.
The inner disk surrounding XUE 1, as revealed by the team, closely resembles those in nearby star-forming regions, according to Rens Waters of Radboud University in the Netherlands. Detection of water, along with molecules like carbon monoxide, carbon dioxide, hydrogen cyanide, and acetylene, provides valuable insights. However, the observed emission is weaker than some models predicted, indicating a potentially smaller outer disk radius. The groundbreaking aspect, highlighted by Lars Cuijpers of Radboud University, is the first-time detection of these molecules under extreme conditions.
Additionally, the team identified small, partially crystalline silicate dust at the disk’s surface, considered the building blocks of rocky planets. These findings bode well for rocky planet formation, suggesting that the inner disk’s conditions mirror those in well-studied regions where only low-mass stars form. This challenges previous assumptions, indicating that rocky planets can potentially form in a much broader range of environments than previously believed.
The XUE 1 spectrum shows the presence of CO.
The spectral data from the protoplanetary disk, XUE 1, situated in the star cluster Pismis 24, unveils observed signatures of carbon monoxide across the range of 4.95 to 5.15 microns. This insight into XUE 1 serves as a vital step in understanding the conditions conducive to rocky planet formation. The team emphasizes that additional observations from the ongoing XUE program are crucial to establishing the prevalence of these conditions.
Lead researcher Ramírez-Tannus states, “XUE 1 shows us that the conditions to form rocky planets are there, so the next step is to check how common that is. We will observe other disks in the same region to determine the frequency with which these conditions can be observed.” The findings have been detailed in The Astrophysical Journal, marking a significant contribution to our understanding of planet formation in extreme environments.