JWST uses interferometry mode to reveal two protoplanets around a young star

JWST is flexing its muscles with its interferometry mode. Researchers have used it to study a known extrasolar system called PDS 70. The goal? To test the interferometry mode and see how it works when observing a complex target.

The mode uses the telescope’s NIRISS (Near Infrared Imager and Slitless Spectrograph) as an interferometer. It’s called Aperture Masking Interferometry (AMI) and it allows JWST to reach its highest level of spatial resolution.

A team of astronomers used JWST’s AMI to observe the PDS 70 system. PDS 70 is a young T-Tauri star about 5.4 million years old. At that young age, its protoplanetary disk still surrounds it. PDS 70 is a well-studied system that has attracted the attention of astronomers. It is unique in that its two planets, PDS 70 bic, make it the only known multiplanetary protoplanetary disk system.

The researchers wanted to determine how easily the AMI would find the two known planets in PDS 70 and what else it might observe in the system.

His research paper is titled “The James Webb Interferometer: Space-based interferometric detections of PDS 70 b and c at 4.8 µm”. It is available on the preprint server archiv and has not yet been peer reviewed. The lead author is Dori Blakely of the Department of Physics and Astronomy at the University of Victoria, BC, Canada.

PDS 70 is known for its pair of planets. PDS 70 b is about 3.2 Jupiter masses and follows an orbital period of 123 years. PDS 70 c is about 7.5 Jupiter masses and follows a 191-year orbit. One of the most puzzling things about the system is that PDS 70 b appears to have its own accretion disk. The system also shows intriguing evidence of a third body, perhaps another star.

JWST interferometry easily detected both planets. Indeed, observations found evidence of emissions from circumplanetary discs around PDS 70 bi c. “Our photometry of both PDS 70 b and c provides evidence for circumplanetary disk emission,” the researchers write.

This means we can see the star and its protoplanetary disk, where the planets form, and the individual circumplanetary disks around each planet. These disks are where the moons form, and seeing them in a system 366 light years away is very impressive.

JWST’s AMI observations also found a third point source. Its light is different from the light of the pair of planets and more like the light of the star. If it is another planet, its composition is different from the others. If it’s not another planet, that doesn’t mean it must necessarily be another star. JWST could be seeing scattered starlight from another gaseous and dusty structure or cluster in the disk.

“This indicates that what we observe is not due to a simple inner disc structure, and may indicate a complex morphology of the inner disc, such as a spiral or lumpy features,” the researchers explain.

The third unexplained source could be something more exotic. Previous research also identified the source and suggested it could be an accretion stream flowing between PDS 70 bi c. “We interpret its signal in the direct vicinity of planet c as a trace of the accretion current feeding its circumplanetary disk,” the authors of the previous research wrote.

Or, perhaps most excitingly, the source could be another planet. “Another scenario is that the signal we observe is due to an additional inner planet in the orbit of PDS 70 b,” the authors explain. “Follow-up observations will be needed to determine the nature of this emission,” the authors write.

Part of the success of the observations comes from what it didn’t detect. Protoplanetary disks are dusty and difficult to examine. JWST has a leg up because it can see infrared light. When used in interferometry mode, it is a powerful tool. The fact that I haven’t been able to detect any other planets is progress, though. “Furthermore, we place the deepest constraints on additional planets,” a part of the disc. These constraints will help future researchers examine the PDS 70 system and other extrasolar systems.

The results also show another of AMI’s strengths: its ability to see parts of the parameter space that other telescopes cannot. “Furthermore, our results show that NIRISS/AMI can reliably measure the relative astrometry and contrasts of young planets in a part of the parameter space (small separations and moderate to high contrasts) that is unique to this mode of observation and inaccessible to all other current facilities at 4.8 µm,” the authors explain.

The JWST has already established its place in the history of astronomy. It has fulfilled its promise and has already contributed significantly to our understanding of the cosmos. The telescope’s observations with its aperture masking interferometry mode will further cement its place in history.

“Here, using the power of the James Webb Interferometer, we detect PDS 70, its outer disk, and its two protoplanets, bi c. These are the first planets detected with space-based interferometry,” the authors write.