According to a survey published in The Astronomical Journal by Naman S. Bajaj of the University of Arizona and 12 colleagues, the James Webb Space Telescope has detected escaping gas around 66 out of 72 young planetary systems. The study uses warm hydrogen and ionised neon as tracers of gas leaving their protoplanetary discs.
Webb Target Selection and MIRI Instrumentation Details
The research team reanalysed archival observations from Webb’s Mid-Infrared Instrument, or MIRI. It is not simply collecting a picture.
Extended emission from one or both appeared around 66 of the 72 discs. Those categories can overlap. Indeed, every system with a neon jet also showed a wind traced by molecular hydrogen or oxygen.
Differentiating Jets, Disc Winds, and Photoevaporative Flows
Material in a young disc orbits because it carries angular momentum. Magnetic fields threading the disc can help. The result can take more than one form. Jets are fast and tightly collimated, emerging roughly along the star’s rotational axis. Disc winds are broader and can rise across a larger area. Both remove mass, but their geometry, speed and physical origin need not be identical.
The inclined orientation of the survey’s discs helps separate these structures on the sky. That selection also matters when interpreting the result.
Did you know? Magnetically launched winds do not only destroy a disc. By carrying angular momentum away, they can enable gas to flow inward. The same process that helps organise an accreting system also steadily reduces its mass.
How Accretion Rates Drive Outflow Evolution
The strongest trend was with the rate at which disc material falls on to the star. Detection fractions for both molecular-hydrogen winds and neon jets rose with accretion rate. Hotter H2 wind components disappeared faster as the accretion rate fell than the cooler component did. At lower accretion rates, the fast jets weakened and the remaining wind signatures were predominantly atomic.
The SETI Institute’s account of the study describes the 72 systems as frames in a film.
The Core-Accretion Timeline Problem for Giant Planets
When that core becomes sufficiently massive, its gravity can bind gas efficiently and the envelope grows rapidly. The order is important. The core must be ready while hydrogen and helium still dominate the disc. Jupiter-like worlds do not merely require enough total material at the beginning.
Space Daily previously covered Webb’s atmospheric measurements of the four giant planets around HR 8799. A core that reaches the critical stage early can become a gas giant.
Frequently Asked Questions
How did the James Webb Space Telescope detect escaping gas?
Extended emission from one or both appeared around 66 of the 72 discs.
What is the difference between a jet and a disc wind?
Jets are fast and tightly collimated, emerging roughly along the star’s rotational axis. Disc winds are broader and can rise across a larger area. Both remove mass, but their geometry, speed and physical origin need not be identical.
Why is disc dispersal a problem for forming Jupiter-like planets?
Hydrogen and helium are plentiful around a newborn star, but only while its planet-forming disc survives.
Did researchers track a single disc aging over time?
No. The team observed different systems, not the same disc ageing before the telescope.