New research points to origin of planet formation

Researchers at Texas State University are making big discoveries that better inform the public on the processes behind rocky planet formation.

TXST Department of Physics Assistant Professor Andrea Banzatti is leading the research team, which includes Postdoctoral Research Associate Anusha Kalyaan–an expert in predictive modeling.

“Most processes that we are studying take way too long for us to observe them in real time,” Banzatti said, adding that the only way to view the formation of stars and rocky planets is to view snapshots at different points in the process.

Banzatti said the research utilizes the James Webb Space Telescope Mid-Infrared Instrument data to study two compact and two extended protoplanetary disks, all of which are surrounding young stars that are forming at the center. He said within the inner portion of these disks, new rocky planets are also forming. Disks get their name from their shape, which is flat, and Banzatti said would look like a line if viewed from one angle and a circle if viewed from another.

Extended disks have gaps between rings of various sizes from smaller in the middle to larger on the outer portions like the lines on a record, and compact disks do not have gaps or rings.

“Every young star forms at the center of a disk. The disk is feeding gas to the star,” Banzatti said. “The leftovers of this process are also making planets.”

Banzatti said the disks are composed of dust and gas, and surround every young star that forms in space.

The compact disks could form water-rich super Earths, which are larger than our Earth, due to a larger supply of icy pebbles from their outer disk.

The extended disks with gaps and rings could form planets more similar to the first four rocky planets in our solar system, which are smaller and relatively water-poor, due to an inefficient delivery of icy pebbles from the outer disk.

“This is a fundamental dichotomy in the planet- formation process proposed by theories to be at the origin, possibly, of why some stars have a super earth and other stars don't have it,” Banzatti said. “Our solar system has relatively small planets that are relatively water- poor, and the reason for that could be that our solar system looked like a ringed disk back during the formation.”

Kalyaan said that although the term is pebbles, the sizes of icy pebbles in the disks range from very small to a meter wide.

“They are present everywhere in the disk,” Kalyaan said, adding that if many of the pebbles combine quickly through a process called pebble accretion, “They can quickly add to the mass of something like an asteroid and make it into a planet.”

Kalyaan said as the ice-covered pebbles drift from the outer disk to the inner disk, the pebbles deliver both rock and water to the planets that are forming in the inner disk.

When these pebbles cross the snowline, the ice sublimates into water vapor due to the higher temperature closer to the star, and this vapor is what JWST observes.

“These pebbles are rock and ice. They’re coming in from the outer disk where the temperatures are cold enough for ice to be on the surfaces,” Kalyaan said. “They bring in rocky material into the inner disk and that rocky material can be the building blocks of planets, especially the terrestrial planets [rocky planets similar to Earth and Venus].”

Banzatti added that the mystery behind planetary formation is related to the massive growth required to transform icy pebbles into an entire planet.

“The delivery of solid mass and water to the region where planets are forming is so fundamental in theories of planet formation,” Banzatti said. “We are talking about one of the most important processes that has to happen in order to form planets in a disk like that.”

According to the NASA website, the MIRI has both a camera and a spectrograph that can process light in the mid-infrared region of the electromagnetic spectrum–wavelengths that are too long to be seen by the human eye.

MIRI covers the wavelength range from five to 28 microns. Its sensitive detectors allow it to process the red shifted light of distant galaxies, newly forming stars and faintly visible comets in addition to objects in the Kuiper Belt.

Red-shifted means the wavelength of the light is stretched, so the light is seen as shifted towards the red part of the spectrum.

Banzatti said the research at hand focuses on spectra from water vapor.

He said that the use of spectra is a way to study models without the need to physically obtain the objects being studied, so the research looks at light sources in the universe and disperses them to measure the imprint each molecule and atom gives the light.

It is meant to assist in studying the chemistry of the universe.

He said there is a unique pattern that emerges from the data and indicates that water is present.

Banzatti said he is proud of the opportunity to use JWST data, which he said is an extremely competitive process with applicants from across the world.

“In a very short time, we made a very big discovery,” Banzatti said, noting that the data has only been available to them since February of this year.

To learn more about the JWST go to https://webb. nasa.gov/content/about/ index.html.