How long does it take for planets to form from the disk of gas and dust orbiting a star? A new study led by the University of Arizona gives scientists a better understanding of how our solar system came to be.

Scientists believe that planetary systems, such as our solar system, contain more rocky objects than gas-rich ones. These include the inner planets around our Sun (Mercury, Venus, Earth, and Mars), the asteroid belt, and Kuiper belt objects such as Pluto.

On the other hand, Jupiter, Saturn, Uranus and Neptune contain mostly gas. But scientists have also long known that the disks that form planets initially had 100 times more mass of gas than solids; This raises an urgent question: When and how does most of the gas leave the newly formed planetary system?

Uncovering the secrets of the planetary disk

New research led by Naman Bajaj of the University of Arizona Lunar Planetary Laboratory Astronomy Magazinegives answers. Using the James Webb Space Telescope (JWST), the team captured images of one such newborn planetary system, also known as a circumstellar disk, which is in the process of actively shedding gas into the surrounding space.

“Knowing when gas dissipates is important because it gives us a better idea of ​​how long gaseous planets need to consume gas from their surroundings,” said Bajaj, a second-year postdoctoral researcher at the University of Arizona Lunar Planetary Laboratory. “With unprecedented images of these disks surrounding young stars, the birthplaces of planets, JWST is helping us learn how planets form.”

The formation process of planets

According to Bajaj, in the very early stages of the formation of a planetary system, planets coalesce into a disk of gas and small dust orbiting a young star. These particles stick together to form increasingly larger pieces called planetoids. Over time, these planetoids collide and stick together to form planets. The type, size and location of planets formed depend on the amount of material present and how long it remains in the disk.

“So in short, the outcome of planet formation depends on the evolution and propagation of the disk,” Bajaj said. said.

The discovery follows the observation that T Cha, a young star about 4.6 billion years old relative to the Sun, is surrounded by an erosive circumstellar disk characterized by a wide dust gap spanning about 30 astronomical units, or au. is based on. It is the average distance between the Earth and the Sun.

For the first time, Bajaj and his team managed to image the disk wind, which is the name given to the gas that gradually separates from the disk that forms the planet. Astronomers took advantage of the telescope’s sensitivity to light emitted by an atom when high-energy radiation hits one or more electrons in the atom’s nucleus, as in starlight. This is known as ionization, and the light emitted in the process can be used as a type of chemical “fingerprint” that tracks neon and argon, two noble gases, in the case of the T Cha system. The observations also mark the first time double ionization of argon has been detected in a planet-forming disk, the team wrote in the paper.

“The neon signature in our images tells us that the disk wind is coming from a large region away from the disk,” Bajaj said. “These winds can be driven either by high-energy photons (essentially light escaping from the star) or by the magnetic field penetrating the planet-forming disk.”

Stellar impacts and evolving disks

This time with a Ph.D. from Leiden University in the Netherlands. To tell them apart, the same group, led by Andrew Selleck, simulated the scattering caused by stellar photons, the intense light emitted from a young star. They compared these simulations with actual observations and found that scattering of high-energy stellar photons could explain the observations and thus could not be ruled out as a possibility. This study concluded that the amount of gas emitted from the T Cha disk each year is equivalent to the amount of gas emitted by Earth’s satellite. These results will be published in a companion paper currently under review in the Astronomical Journal.

Although neon signatures have been detected in many other astronomical objects, they were not known to originate from low-mass planet-forming disks until they were first detected in 2007 by Ilaria Pascucci, a professor at LPL, who soon identified them as tracer disk winds. . These early discoveries revolutionized research efforts aimed at understanding the scattering of gas from circumstellar disks. Pascucci is the principal investigator of the latest observational project and co-author of the publications reported here.

“Our discovery of spatially resolved neon emission with the James Webb Space Telescope and the first detection of doubly ionized argon may be the next step in transforming our understanding of how gas is cleared from the planet-forming disk,” Pascucci said. said. “This understanding will help us better understand its history and impact on our own solar system.”

Additionally, the team found that T Cha’s inner disk evolved over a very short time period of decades; They found that the spectrum observed by JWST was different from the previous spectrum detected by Spitzer. According to second-year LPL doctoral student Chenyang Xie, who is leading this ongoing study, this discrepancy could be explained by a small asymmetric disk inside T Cha that lost some of its mass in the short 17 years between the two. observations.

“Together with other studies, this also indicates that the T Cha disk has reached the end of its evolution,” Xie said. “We may witness the entire mass of dust in T Cha’s inner disk dissipating within our lifetime.”