Astronomers using the NASA/ESA/CSA James Webb Space Telescope have detected abundant water, carbon monoxide, carbon dioxide, hydrogen cyanide and acetylene in the inner few astronomical units (AU) of XUE 1, a highly irradiated protoplanetary disk in the Lobster Nebula. The findings imply that the inner regions of highly irradiated disks can retain similar physical and chemical conditions to disks in low-mass star-forming regions, thus broadening the range of environments with similar conditions for rocky planet formation to the most extreme star-forming regions in our Galaxy.
An artist’s impression of the massive star-forming region, with the planet-forming disk XUE 1 in the foreground. Image credit: Maria Cristina Fortuna, www.mariacristinafortuna.com.
Protoplanetary disks are vast, spinning clouds of gas, dust, and chunks of rock where planets form and evolve.
These regions are representative of the environment in which most planetary systems formed.
Understanding the impact of environment on planet formation is important for scientists to gain insights into the diversity of the different types of exoplanets.
Protoplanetary disks are the targets of the eXtreme Ultraviolet Environments (XUE) James Webb Space Telescope program.
Thanks to Webb, astronomers can now study the effect of UV radiation on the inner rocky-planet forming regions of protoplanetary disks around stars like our Sun.
“Webb is the only telescope with the spatial resolution and sensitivity to study planet-forming disks in massive star-forming regions,” said Dr. María Claudia Ramírez-Tannus, an astronomer at the Max Planck Institute for Astronomy.
Dr. Ramírez-Tannus and colleagues aimed to characterize the physical properties and chemical composition of the rocky-planet-forming regions of 15 protoplanetary disks in three areas of the Lobster Nebula using the Medium Resolution Spectrometer on Webb’s Mid-Infrared Instrument (MIRI).
“We are examining 15 planet-forming disks around young solar-mass stars influenced by strong UV radiation emitted by numerous nearby massive stars,” said Pennsylvania State University’s Professor Konstantin Getman.
“This emission has the potential to alter the planet-forming process.”
Also known as NGC 6357, the Lobster Nebula is a large emission nebula roughly 5,500 light-years away from Earth in the constellation of Scorpius.
The nebula is one of the youngest and closest massive star-formation complexes, and is host to some of the most massive stars in the Milky Way.
Massive stars are hotter, and therefore emit more ultraviolet radiation. This can disperse the gas, making the expected lifetime of the disk as short as a million years.
One of the protoplanetary disks studied by the team, XUE 1, is located in the star cluster Pismis 24.
“Within the inner regions of a highly irradiated disk called XUE 1, we discovered molecules containing water and carbon,” Professor Getman said.
“The presence of these molecules indicates that Earth-like planets may form in a diverse range of environments.”
“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,” said Dr. Arjan Bik, an astronomer at Stockholm University.
Due to its location near several massive stars in the Lobster Nebula, the 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 terrestrial planets.
“We find that the inner disk around XUE 1 is remarkably similar to those in nearby star-forming regions,” said Dr. Rens Waters, an astronomer at Radboud University.
“We’ve detected water and other molecules like carbon monoxide, carbon dioxide, hydrogen cyanide and acetylene.”
“However, the emission found was weaker than some models predicted. This might imply 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,” said Dr. Lars Cuijpers, an astronomer at Radboud University.
The team also found small, partially crystalline silicate dust at the surface of XUE. This is considered to be the building blocks of rocky planets.
“XUE 1 shows us that the conditions to form rocky planets are there, so the next step is to check how common that is,” Dr. Ramírez-Tannus said.
“We will observe other disks in the same region to determine the frequency with which these conditions can be observed.”
The results appear in the Astrophysical Journal.
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María Claudia Ramírez-Tannus et al. 2023. XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Protoplanetary Disk. ApJL 958, L30; doi: 10.3847/2041-8213/ad03f8
