James Webb Space Telescope Snaps Its First Image of a Protoplanetary Disk

Artist’s impression of a protoplanetary disk

Credit: NASA / JPL-Caltech

Artist’s impression of a protoplanetary disk

In the last few decades, scientists have identified thousands of exoplanets scattered across the cosmos. All these worlds, from the largest gas giants to the tiniest rocky globes, began as a cloud of dust and gas orbiting a young star. The process by which that occurs is a subject of intense astronomical research, and the James Webb Space Telescope is uniquely equipped to help. Researchers from the University of Arizona’s Steward Observatory have used the new telescope to obtain the deepest look yet at stellar nurseries that spawn new stars and planets.

Past observations of young star systems have laid out the basics; clouds of gas coalesce into dense pockets that eventually grow to become stars capable of nuclear fusion. The remaining material in the system becomes a swirling protoplanetary disk, in which tiny fragments gain mass to become pebbles, planetesimals, and eventually, planets. The specifics are still a mystery because this process occurs in a cocoon of dust and gas that blocks most instruments from getting a clear view.

Webb is ideal for this work not only because it has a mirror 6.5 times larger than Hubble’s but also because its instruments operate in infrared. At these wavelengths of light, it is possible to peer through the envelope of gas that obscures the happenings in young solar systems. To test Webb’s protoplanetary skills, the team pointed it at several well-studied protostars, including HL Tauri (also called HL Tau). Previous observations with the ALMA radio observatory and other instruments have identified gaps in the disk that could indicate protoplanets sweeping dust out of the way.

The UArizona team was reportedly impressed by the level of detail in Webb’s images. However, the observatory was not able to spot the suspected exoplanets. HL Tau isn’t very far away in the grand scheme of things, either. It’s in the Taurus star-forming region, about 457 light-years from Earth.

HL Tau Webb

Solar system HL Tau with gap outlines from ALMA and material flowing in toward the star (orange) as seen by Webb. Credit: Camryn Mullin et al.

One of the newly published studies on the project notes that the observatory’s primary NIRCam instrument probably does not see far enough into the infrared to spot the glint of exoplanets amid the cloud of dust. Meanwhile, Webb’s MIRI instrument operates at longer wavelengths but doesn’t have enough angular resolution. “No current instruments have the resolution and wavelength range required for such an observation,” the study says.

Webb might not be able to spot still-forming protoplanets, but it can see distant worlds after solar systems have settled down. The team was surprised to see details of the proto-stellar envelope, a complex current of dust and gas surrounding the star itself. Material falls inward toward the star, increasing its mass and giving it fuel to burn. “We see a very complex and dynamic system with ‘streamers’ feeding material from the outer envelope into the inner regions of the disk, where we expect planets to be forming,” said study lead Jarron Leisenring.

This data will help scientists refine ideas about how planets come to be, but Webb won’t unlock all the secrets. It may take another generation of space telescope development before we can examine the earliest phases of planetary formation.