By observing two young planet-forming disks, the JWST has detected an excess of water vapor, which is believed to originate from icy pebbles migrating inwards from the outer regions of the disks.
This inward migration of icy pebbles, known as pebble accretion, is a key process in the formation of planets. As these pebbles collide and stick together, they gradually grow into larger objects, eventually forming protoplanets. The presence of water vapor in the inner regions of the disks suggests that this process is indeed occurring, lending support to the pebble accretion theory.
The JWST observations were made using its Mid-Infrared Instrument (MIRI), which is sensitive to faint infrared emissions. The telescope detected water vapor in two disks, located in the Taurus star-forming region about 430 light-years away. These disks are both relatively compact, indicating that they have already undergone significant inward migration of material.
In contrast, two other disks that were observed by the JWST, belonging to systems named CI Tau and IQ Tau, showed no signs of water vapor. These disks are more extended, suggesting that they have not experienced as much inward migration. This difference in water vapor abundance between the two types of disks suggests that pebble accretion may be more efficient in compact disks.
The JWST observations have also raised intriguing questions about the process of ring formation in planet-forming disks. Images taken by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile show rings in the two extended disks, CI Tau and IQ Tau. However, the two compact disks, GK Tau and HP Tau, show no evidence of rings. Scientists are still investigating how these rings form and how they affect planet formation.
Overall, the JWST observations have provided significant new insights into the process of planet formation. By detecting water vapor in the inner regions of planet-forming disks, the telescope has strengthened the evidence for pebble accretion as a key mechanism in planetary growth. Further observations with the JWST are expected to shed even more light on this fascinating process.