Astronomers have observed water and other molecules for the first time in the highly irradiated inner, rocky-planet-forming regions of a disk in one of our galaxy’s most extreme environments. These findings suggest that the conditions for the formation of terrestrial planets can occur in a broader range of environments than previously thought.
An international team of astronomers used NASA’s James Webb Space Telescope to observe water and other molecules for the first time in the highly irradiated inner, rocky-planet-forming regions of a disk in one of our galaxy’s most extreme environments. These findings suggest that the conditions for the formation of terrestrial planets can occur in a broader range of environments than previously thought.
These are the first results from the James Webb Space Telescope program eXtreme Ultraviolet Environments (XUE), which focuses on the characterization of planet-forming disks (vast, spinning clouds of gas, dust, and chunks of rock where planets form and evolve) in massive star-forming regions. These areas are most likely representative of the conditions under which most planetary systems formed. Understanding the impact of the environment on planet formation is critical for scientists to gain insight into the diversity of exoplanet types.
We find that the inner disk around XUE 1 is remarkably similar to those in nearby star-forming regions. We found water as well as other molecules such as carbon monoxide, carbon dioxide, hydrogen cyanide, and acetylene. However, the observed emission was weaker than some models predicted. This could indicate a small outer disk radius.
Rens Waters
The XUE program seeks 15 disks in three areas of the Lobster Nebula (also known as NGC 6357), a large emission nebula in the constellation Scorpius located approximately 5,500 light-years from Earth. The Lobster Nebula is one of our galaxy’s youngest and closest massive star-formation complexes, and it is home to some of the most massive stars. Because massive stars are hotter, they emit more ultraviolet (UV) radiation. This can disperse the gas, resulting in a disk lifetime of only a million years. Astronomers can now study the effect of UV radiation on the inner rocky-planet-forming regions of protoplanetary disks around stars like our Sun, thanks to Webb.
“Webb is the only telescope with the spatial resolution and sensitivity to study planet-forming disks in massive star-forming regions,” said team lead María Claudia Ramírez-Tannus of the Max Planck Institute for Astronomy in Germany.
Astronomers aim to characterize the physical properties and chemical composition of the rocky-planet-forming regions of disks in the Lobster Nebula using the Medium Resolution Spectrometer on Webb’s Mid-Infrared Instrument (MIRI). This first result focuses on the protoplanetary disk termed XUE 1, which is located in the star cluster Pismis 24.
“Only the MIRI wavelength range and spectral resolution allow us to probe the molecular inventory and physical conditions of the warm gas and dust where rocky planets form,” added team member Arjan Bik of Stockholm University in Sweden.
Due to its location near several massive stars in NGC 6357, scientists expect XUE 1 to have been constantly exposed to high amounts of ultraviolet radiation throughout its life. However, in this extreme environment the team still detected a range of molecules that are the building blocks for rocky planets.
“We find that the inner disk around XUE 1 is remarkably similar to those in nearby star-forming regions,” said Radboud University in the Netherlands team member Rens Waters. “We found water as well as other molecules such as carbon monoxide, carbon dioxide, hydrogen cyanide, and acetylene. However, the observed emission was weaker than some models predicted. This could indicate a small outer disk radius.”
“We were surprised and excited because this is the first time that these molecules have been detected under these extreme conditions,” Radboud University’s Lars Cuijpers added. At the disk’s surface, the team discovered small, partially crystalline silicate dust. This is thought to be the foundation of rocky planets.
These findings are encouraging for the formation of rocky planets because the scientists discovered that the conditions in the inner disk are similar to those found in well-studied disks in nearby star-forming regions, where only low-mass stars form. This implies that rocky planets can form in a much wider variety of environments than previously thought.
The team emphasizes the importance of the remaining XUE program observations in determining the commonality of these conditions.
“XUE 1 shows us that the conditions to form rocky planets are there, so the next step is to check how common that is,” he said. “We will observe other disks in the same region to determine the frequency with which these conditions can be observed.”
