Webb Study Reveals Rocky Planets Can Form in Extreme Environments

Focusing on one of the most extreme environments in our galaxy, the results suggest that conditions for the formation of terrestrial rocky planets can occur in a possible broader range of environments than previously thought. The research, ‘XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Protoplanetary Disk,’ is detailed in The Astrophysical Journal.

These are the first results from the eXtreme Ultraviolet Environments (XUE) programme, which focuses on characterising planet-forming disks in massive star-forming regions.

These regions likely represent the environment in which most rocky planets are formed. Understanding the impact of the environment on planet formation is important for scientists to gain insights into the diversity of the different types of exoplanets.

The XUE programme targets a total of 15 disks in three areas of the Lobster Nebula (also known as NGC 6357), a large emission nebula roughly 5,500 light-years away from Earth in the constellation Scorpius.

The Lobster Nebula is one of the youngest and closest massive star-formation complexes and hosts some of the most massive stars in our galaxy. Massive stars are hotter and emit more ultraviolet (UV) radiation.

Thanks to Webb, astronomers can now study the effect of UV radiation on the regions that form rocky planets and protoplanetary disks around stars like our Sun.

“The James Webb Space Telescope 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 characterise 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.

Arjan Bik of Stockholm University explained: “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.”

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 were surprised and excited because this is the first time that these molecules have been detected under these extreme conditions,” commented Lars Cuijpers of Radboud University.

The team also found small, partially crystalline silicate dust at the disk’s surface. This is considered to be the building blocks of a rocky planet.

These results are good news for the study of planet formation, as the science team finds that the conditions in the inner disk resemble those found in the well-studied disks located in nearby star-forming regions, where only low-mass stars form.

This suggests that rocky planets can form in a much broader range of environments than previously believed.

The team notes that the remaining observations from the XUE programme are crucial to establishing 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,” concluded Ramírez-Tannus. “We will observe other disks in the same region to determine the frequency with which these conditions can be observed.”

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