The Taurus star-forming region is only a few hundred light-years away, and it may be the nearest star formation region to Earth. It’s a stellar nursery with hundreds of young stars, and attracts a lot of astronomers’ attention. One of the young stars in Taurus is named IRAS 04302. IRAS 04302 is sometimes called the “Butterfly Star” because of its appearance when viewed edge-on.
The JWST image of IRAS 04302 is the latest ESA/Webb Picture of the Month.
Astronomers are intensely interested in the details of planet formation, and one of the JWST’s science goals is the study of planets forming in protoplanetary disks around young stars like IRAS 04302. Many of the images we have of planets forming in protoplanetary disks come from ALMA, the Atacama Large Millimeter/submillimeter Array. These images show the disks in a “top down” orientation. In those images, astronomers can spot the rings and gaps that signal planet formation.
ALMA has captured many images of protoplanetary disks around young stars. These three are typical, and show gaps and rings where planets are likely forming. As young planets take shape, they sweep up gas and dust in the disk, creating the gaps. Image Credit: ALMA/ESO
IRAS 04302 is oriented so that we see its protoplanetary disk from the side. IRAS 04302 is a fine example of a young star that is still accreting mass while planets could be forming in its protoplanetary disk, and the edge-on view provides more than just a pretty picture. This viewpoint gives astronomers a different look at disks. It shows the disk’s vertical structure and can reveal how thick the dusty disk is.
In this image, the dust disk acts almost like a coronagraph, blocking out some of the star’s light and making detail in the disk stand out. Reflection nebulae on either side of the disk are illuminated by the star, giving IRAS 04302 its nickname Butterfly Star.
The image is created from the JWST’s Mid-Infrared Instrument (MIRI) and Near-Infrared Camera (NIRCam), and the Hubble also contributed optical data. The Webb shows how dust grains are distributed and how dust extending out from the disk reflects near-infrared light. The Hubble shows the dust lane itself, as well as clumps and streaks, evidence that the star is still gathering mass. It also shows jets and outflows, more evidence of its ongoing growth.
IRAS 04302 as imaged with the JWST. The disk is about 65 million km across, making it several times larger than our Solar System. Image Credit: ESA/Webb, NASA & CSA, M. Villenave et al. LICENCE: CC BY 4.0 INT
There’s no scientific journal devoted solely to protoplanetary disk, but there could be, considering how much research goes into them. These JWST images are more than just pictures, they’re associated with a study published in The Astrophysical Journal titled “JWST Imaging of Edge-on Protoplanetary Disks. II. Appearance of Edge-on Disks with a Tilted Inner Region: Case Study of IRAS04302+2247.” The lead author is Marion Villenave from NASA’s Jet Propulsion Laboratory.
“Because planet formation occurs in the protoplanetary disk phase, studying protoplanetary disk evolution can allow us to better understand planet formation,” the article’s authors write. The main thrust of this type of research is to understand how tiny dust particles gradually form kilometer-sized bodies that eventually form planetesimals and then planets. It can take only a few million years, or even less, for these kilometer-size rocks to form. One of the big questions is sometimes called the “Bouncing Barrier.” The problem is that once dust grains reach a certain size, their collisions are more energetic. Instead of sticking to one another, they bounce off each other. For planetesimals to form, some force has to overcome the Bouncing Barrier.
This figure from the research is an image gallery of the JWST observations of IRAS04302. Image Credit: M. Villenave et al. 2025. ApJ
“In the current paradigm, high dust concentrations are thought to accelerate grain growth by promoting disk instabilities that lead to planetesimal formation (e.g., streaming instability), and subsequently allowing efficient growth via pebble accretion,” the authors write.
Answers to the Bouncing Barrier and other questions regarding planet formation can only be found in protoplanetary disks. In this research, the scientists examined IRAS 04302’s edge-on disk hoping to find clues. One of the answers to planet formation questions may lie in dust settling.
“Dust vertical settling in the disk is the result of gas drag on dust grains subject to stellar gravity and gas turbulence,” the authors write. “This mechanism leads large dust grains to fall into the disk midplane and accumulate there, which is favorable for planet formation.” The authors note that this mechanism is poorly constrained by observations.
This is why IRAS 04302 is such a desirable target.
“Highly inclined protoplanetary disks are favorable targets to investigate this mechanism because they allow a direct view of the disk’s vertical structure,” the researchers explain.
The authors observed that IRAS 04302’s inner disk is tilted and asymmetrical, as are 15 out of 20 other observed edge-on disks. If tilt and asymmetry are this common, it has implications. It affects how disks evolve and how their dynamics play out. In turn, it must affect how planets form, and what the eventual architecture of a solar system will be.
This figure shows 20 observed edge-on disks. 15 of them show clear asymmetry, while five do not. Though the five that are considered symmetrical have some curves, they’re not curved enough to be considered asymmetrical. Image Credit: M. Villenave et al. 2025. ApJ
The researchers didn’t reach a clear conclusion for how all of this works. No single study can answer all of our questions, but each one nudges us toward a greater understanding. They note that further observations will deepen their understanding of tilted disks and how they affect planet formation.