Unveiling Planet Formation: The PDS 70 System Through the Eyes of JWST

In the vast expanse of the cosmos, planets are born from swirling disks of gas and dust that encircle young stars. This intriguing process of planet formation has captivated astronomers, and understanding it is a key objective of the James Webb Space Telescope (JWST). One of the most promising targets in this quest is PDS 70, a nearby star that is home to two nascent planets, PDS 70b and PDS 70c, which are among the few exoplanets that have been directly imaged.

Situated approximately 370 light-years away, PDS 70 is an orange dwarf star hosting two young, growing planets. The European Southern Observatory’s Very Large Telescope (VLT) made headlines in 2018 when it successfully captured direct images of both planets using its innovative SPHERE instrument. Notably, PDS 70b holds the distinction of being the first protoplanet ever imaged directly, paving the way for further exploration of the planet formation process.

Recently, researchers employed a new observational strategy with the JWST to delve deeper into the PDS 70 system. The findings are detailed in a recent paper published in The Astronomical Journal, led by Dori Blakely, a graduate student in Physics and Astronomy at the University of Victoria, BC, Canada. The JWST’s Near Infrared Imager and Slitless Spectrograph (NIRISS) utilized a technique known as Aperture Masking Interferometry (AMI), which enhances the telescope’s resolution by creating an interferogram that effectively increases the size of the telescope.

The results of this innovative approach were groundbreaking. The researchers reported evidence of material surrounding both PDS 70b and PDS 70c, reinforcing the notion that these planets are still in the process of formation. “This is like seeing a family photo of our Solar System when it was just a toddler,” Blakely remarked in a press release, emphasizing the significance of these observations.

Previous studies of the PDS 70 planets were conducted at shorter wavelengths, which were interpreted through models for low-mass stars and brown dwarfs. However, the JWST’s ability to observe at longer wavelengths revealed more light than earlier observations could explain, suggesting the presence of warm material around both planets. This material is interpreted as being part of a circumplanetary disk, which is crucial for the planets’ growth.

The star itself, a T-Tauri star only about 5.4 million years old, is still actively accreting material and has not yet transitioned to the Main Sequence, which it won’t reach for tens of millions of years. This dynamic environment provides a rare opportunity to observe planetary formation in real-time. Doug Johnstone, a co-author from the Herzberg Astronomy and Astrophysics Research Centre, stated, “Seeing planets in the act of accreting material helps us answer long-standing questions about how planetary systems form and evolve.”

Moreover, this new research lends additional credence to the existence of a potential third planet in the PDS 70 system, tentatively named PDS 70d. Previous hints of this third planet emerged in a 2024 paper, but uncertainties surrounded its nature. The latest findings help constrain some properties of this object, regardless of whether it is indeed a planet or merely a dust clump. If confirmed, PDS 70d would likely exhibit a different atmospheric composition compared to its sibling planets.

The implications of these discoveries extend far beyond the PDS 70 system. By observing the mechanisms of planet formation in action, astronomers are piecing together the puzzle of how planetary systems, including our own, come to be. As follow-up observations are planned, the astronomical community eagerly anticipates further insights into the nature of PDS 70 and its intriguing planets.