Thursday, 9 November 2023 – 12:39 WIB
VIVA – The James Webb Space Telescope (JWST) or the James Webb Space Telescope has observed planet-forming disks emitting cold “vapor,” providing important evidence for the leading theory explaining how planets form.
This excess water vapor was detected by the James Webb Space Telescope in two disks of gas and dust surrounding young stars that are only 2 million to 3 million years old, which is very young in the scope of our universe’s timeline. The disk is located in the star-forming region of Taurus, which is about 430 light years away.
Astronomers believe that planets form through a process that begins with what is called “pebble accretion.” It involves small chunks of silicate rock, ranging in size from a centimeter to about a metre, covered in ice.
They are thought to begin their lives on the outside of frozen planet-forming disks, usually home to comets, and eventually begin to experience friction with the gas within the disk.
This friction may rob the pebble of orbital energy and cause it to migrate to the interior of the disk.
As they gathered in the inner world, the pebbles are thought to have started colliding with each other and sticking together, slowly growing into larger and larger objects until they became protoplanets.
From there, the protoplanet’s much stronger gravity allowed them to sweep up the pebbles at a faster rate, accelerating their growth. That’s the long-standing theory of planet formation.
The water vapor detected by JWST’s Mid-Infrared Instrument (MIRI) is evidence of this process because this type of water is thought to originate from migrating ice pebbles.
Illustration of an asteroid approaching Earth.
As ice pebbles drift inward, they are believed to cross a boundary called the “snow line.” In our solar system, the snow line is just inside Jupiter’s orbit when the planets formed.
Within this limit, the temperature inside the disk is considered too high to allow water to become ice. The layer of ice on the gravel will evaporate, causing the injection of cold water vapor into the interior of the disc.
“Webb finally uncovered the connection between water vapor in the inner disk and the movement of ice pebbles from the outer disk,” Andrea Banzatti of Texas State University, lead author of a new paper describing the JWST observations, said in a statement.
JWST observed a total of four planet-forming disks, two disks that were quite compact, and two disks that were elongated and did not experience much inward migration. Water vapor was only found in two compact disks.
However, there are still unanswered questions. For example, two expanded disks, belonging to systems named CI Tau and IQ Tau, appear like rings in images taken by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.
How these rings form is still debated, but one theory is that when migrating gravel encounters an area of higher pressure, the flow into it slows.
Illustration of Earth and Moon.
The deceleration is thought to hold the pebble inside this kind of pressure trap, forcing it to manifest as a ring. However, how these rings affect the formation of planets due to the addition of gravel in them is still unclear.
It is also interesting that two compact disks, called GK Tau and HP Tau, show no evidence of a ring-like structure.
Another open question concerns the accretion process — what conditions are necessary for pebbles to stick together when they collide and form larger objects without breaking apart?
JWST observations supporting inward migration of gravel suggest an answer to this puzzle, but we just need to find out what the answer is. JWST hopes to be key, this observatory can help strengthen a more modern picture of how planets form.
“In the past, we had a very static picture of planet formation, almost like isolated zones where planets formed,” said Colette Salyk of Vassar College in New York, who is one of the authors of the paper explaining the JWST results.
“Now we have evidence that these zones can interact with each other.”
Salyk also points out that pebble accretion is thought to have occurred 4.5 billion years ago in our solar system, meaning JWST’s observations tell us not only about how exoplanets formed, but also how our planet Earth was born.
2023-11-09 05:39:57
#James #Webb #Telescope #Finds #Clues #Earths #Origins
