Clemson grad student’s study sheds light on planet formation in infant stars

A little over three decades ago, we didn’t know any planets existed in the universe except those that orbit our sun.

But the advent of more powerful ground-based telescopes and new space-based observatories since then has led to the discovery of thousands of exoplanets, or planets that orbit around stars other than our sun.

The vast majority of the exoplanets that have been found orbit older stars, said Janus Kozdon, a graduate student in the Clemson University Department of Physics and Astronomy. 

Very few have been found orbiting stars in their infancy, where they are gravitationally collecting gas and dust and forming a protoplanetary disk, he said.

“The reason why planets have not been detected very much in these young stars with disks is because the disk itself can hide the planet. It obscures its signature,” Kozdon said. 

Validation

Kozdon and his colleagues validated a novel technique to study forming planets in young stars via the disk’s morphology.

Kozdon will present the research at the June American Astronomical Society meeting  in Madison, Wisconsin. He was the first author of a paper published in the Astronomical Journal in August 2023 titled “Rovibrational Spectrocscopy of CI Tau — Evidence of a Multicomponent Eccentric Disk Induced by a Planet.”  

CI Tau is a young star, about 2 million years old, located approximately 523 light-years away from Earth in the constellation Taurus. A close-in exoplanet was already discovered to still inhabit the protoplanetary disk. Thus, CI Tau served as a one-of-a-kind opportunity to study planet-disk interactions.

Nine nights

Kozdon observed CI Tau for nine consecutive nights — the time it took for the exoplanet to make one full orbit — in January 2022. 

Using spectroscopy and a model he created, Kozdon analyzed gas in the protoplanetary disk — specifically carbon monoxide — to reveal its kinematic behavior and spatial extent. His research showed that the disk is separated into two components (inner and outer), each with opposite orientations, providing evidence for the planet’s existence.

The findings were the first empirical evidence of disk eccentricities being potentially induced by an embedded planet.

Sean Brittain, Clemson’s associate provost and dean of undergraduate learning; Jeffrey Fung, assistant professor in the Department of Physics and Astronomy; and physics graduate students Stanley Jensen and John Kern also worked on the project. Researchers/ collaborators from the University of Maryland, the National Science Foundation National Optical-Infrared Astronomy Research Laboratory and Texas State University were also involved in the research.