Rocky Planets Found to Form in Highly Adverse Environments, Webb Observations Reveal

The James Webb Space Telescope, a collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), has made a groundbreaking discovery. Scientists using the telescope have found water and other important molecules within the inner regions of a protoplanetary disk located around a star. What makes this finding even more remarkable is that the star is situated in one of the most extreme environments in our galaxy, where massive stars are formed.

Traditionally, rocky planet formation is observed in protoplanetary disks around low-mass stars. However, the new results from the James Webb Space Telescope suggest that rocky planets can form in a broader range of environments. This discovery was made as part of Webb’s new eXtreme UV Environments (XUE) program, which aims to study planet-forming disks in various environments throughout our galaxy, specifically regions where massive stars form. These regions have similar conditions to where most planetary systems formed, and understanding their influence on planetary formation can provide insights into the diversity of exoplanets.

The observations were conducted on 15 disks in three distinct areas of the Lobster Nebula (NGC 6357), a large emission nebula located approximately 5,500 light-years away from Earth in the constellation Scorpius. The Lobster Nebula is one of the youngest and closest stellar nurseries to our planet and is home to some of the most massive stars in the galaxy.

But why are scientists particularly interested in how massive stars affect planetary formation? Massive stars are much hotter than low-mass stars like our Sun, emitting more ultraviolet (UV) radiation into their surroundings. This UV radiation disperses the gas within protoplanetary disks surrounding massive stars, shortening their lifespan to just a few million years. Scientists have long theorized about how these hostile conditions would impact planetary formation, and with the James Webb Space Telescope, they are finally getting answers.

Lead author María Claudia Ramírez-Tannus from the Max Planck Institute for Astronomy in Germany explains that Webb is the only telescope with the necessary spatial resolution and sensitivity to study planet-forming discs in regions where massive stars are formed. To characterize the physical and chemical properties of the rocky-planet-forming regions of protoplanetary disks in the Lobster Nebula, the team used Webb’s Medium Resolution Spectrometer, which is part of the Mid-InfraRed Instrument on the telescope. The first set of results focused on a protoplanetary disk named XUE 1 in the star cluster Pismis 24.

The observations surprised the team, as they identified a wide range of molecules essential for rocky planet formation, including water, carbon monoxide, carbon dioxide, hydrogen cyanide, and acetylene. However, the emission was weaker than some models predicted, suggesting a small outer disc radius. Co-author Rens Waters from Radboud University in the Netherlands expressed excitement about these findings, as they are the first time such molecules have been detected under such extreme conditions.

This initial set of results from the James Webb Space Telescope indicates that rocky planet formation within the disks of massive stars is similar to that around low-mass stars. Further observations will be necessary to confirm these theories and hypotheses. However, this discovery suggests that rocky planets can form in a variety of environments and protoplanetary disks, not just around low-mass stars.

Ramírez-Tannus emphasizes that XUE 1 shows that the conditions for rocky planet formation exist in extreme environments. The next step will be to observe other disks in the same region to determine how frequently these conditions can be observed.

The results from Ramírez-Tannus et al. were published in The Astrophysical Journal on November 30, 2023. This groundbreaking discovery opens up new possibilities for understanding planetary formation and the potential habitability of planets in extreme environments. The James Webb Space Telescope continues to push the boundaries of our knowledge, revolutionizing our understanding of the universe and the diversity of planetary systems.