Drifting pebbles supply water to interior regions of planet-forming disks
How are planets born? Scientists have long proposed that ice-covered pebbles are the seeds of planet formation. These icy solids are thought to drift toward the newborn star from the cold, outer reaches of the disk surrounding it. The theory predicts that when these pebbles entered the hottest region, closer to the star, they would release significant amounts of cold water vapor, bringing both water and solids to the nascent planets.
Now the James Webb Space Telescope witnessed this process in action, revealing the connection between water vapor in the inner disk and drifting icy pebbles from the outer disk. This discovery opens up exciting new perspectives in the study of the formation of rocky planets.
Findings from NASA’s Webb Space Telescope support long-proposed planet formation process
Scientists use NASAThe James Webb Space Telescope has just made a revolutionary discovery by revealing how planets are made. By observing water vapor in protoplanetary disks, Webb confirmed a physical process involving the drift of ice-covered solids from the outer regions of the disk into the area of rocky planets.
Theories have long proposed that icy pebbles forming in the cold, outer regions of protoplanetary disks – the same area where comets originate in our solar system – should be the fundamental seeds of planet formation. The main requirement of these theories is that the pebbles drift toward the star due to friction in the gaseous disk, delivering both solids and water to the planets.
Confirmation of theoretical predictions
A fundamental prediction of this theory is that when icy rocks enter the warmer region of the “snow line” – where ice turns to vapor – they should release large quantities of cold water vapor. This is exactly what Webb observed.
“Webb finally revealed the connection between water vapor in the inner disk and the drift of icy pebbles from the outer disk,” said principal investigator Andrea Banzatti of Texas State University, San Marcos. , in Texas. “This discovery opens up exciting perspectives for the study of the formation of rocky planets with Webb! »
“In the past, we had this very static picture of planet formation, almost as if there were isolated areas from which planets formed,” said team member Colette Salyk of Vassar College in Poughkeepsie. , New York. “We now have evidence that these areas can interact with each other. This is also something that would have happened in our solar system.
Harnessing the Power of Webb
The researchers used Webb’s MIRI (Mid-Infrared Instrument) to study four disks – two compact and two extended – around Sun-like stars. These four stars are estimated to be between 2 and 3 million years old, which would only be newborns in cosmic time.
Both CDs should experience effective pebble drift, delivering pebbles a distance equivalent to Neptunethe orbit. In contrast, extended disks should have their pebbles held in several rings up to six times the orbit of Neptune.
Webb’s observations were designed to determine whether compact discs have a higher abundance of water in their rocky interior region, as expected if pebble drift is more efficient and provides plenty of solid mass and water to the inner planets . The team chose to use MIRI’s MRS (Medium Resolution Spectrometer) because it is sensitive to water vapor present in the disks.
The results confirmed expectations by revealing an excess of cold water in compact discs, compared to large discs.
As the pebbles drift, whenever they encounter a pressure bump – an increase in pressure – they tend to accumulate there. These pressure traps do not necessarily stop the drift of stones, but they do hinder it. This is what seems to happen in large disks with rings and spaces.
Current research suggests that large planets could cause rings of increased pressure, in which pebbles tend to accumulate. It could also have been a role of Jupiter in our solar system – inhibiting the delivery of rocks and water to our small, rocky, relatively water-poor interior planets.
Solving mysteries with Webb data
When the data first came in, the results were confusing to the research team. “For two months, we were stuck on these preliminary results that told us that compact discs had colder water, and that large discs had warmer water overall,” Banzatti recalls. “This made no sense, because we had selected a sample of stars with very similar temperatures.”
It was only when Banzatti superimposed the compact disc data on the large disc data that the answer became clear: Compact discs contain very cold water just inside the snow line, about ten times closer than the orbit of Neptune.
“Now we finally see unambiguously that it is the coldest water that has an excess,” Banzatti said. “This is unprecedented and entirely due to Webb’s higher resolving power!”
The team’s results appear in the November 8 edition of Astrophysical journal letters.
Reference: “JWST Reveals Excess Cold Water Near the Snow Line in CDs, Consistent with Cobble Drift” by Andrea Banzatti, Klaus M. Pontoppidan, John S. Carr, Evan Jellison, Ilaria Pascucci, Joan R. Najita, Carlos E. Muñoz-Romero, Karin I. Öberg, Anusha Kalyaan, Paola Pinilla, Sebastiaan Krijt, Feng Long, Michiel Lambrechts, Giovanni Rosotti, Gregory J. Herczeg, Colette Salyk, Ke Zhang, Edwin A. Bergin, Nicholas P. Ballering, Michael R. Meyer and Simon Bruderer, November 8, 2023, Letters from the astrophysical journal.
The James Webb Space Telescope is the world’s first space science observatory. Webb solves the mysteries of our solar system, looks beyond distant worlds around other stars, and probes the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.