Webb reveals that planet-forming disks can last longer than previously thought

If there was something like a cosmic photo album, it could contain a snapshot of a pancake-like disc of gas and dust, swirling around the newly formed stars throughout the Milky Way. Known as planetary formation discs, they are considered to be most, if not all, of young stars, most, if not all, of the short-lived features that provide the raw materials from which planets form.

Most nursery schools on these planets are short-lived, usually lasting only about 10 million years, and are fleeting by cosmic standards. Now, in a surprising discovery, researchers at the University of Arizona have discovered that if a star is less than a tenth of the mass of the sun, the disc can adorn the host stars much longer than previously thought.

In a paper published in the Astrophysical Letters Journal, a research team led by Feng Long of Lunar and Planetary Laboratory at the University of Science reports detailed observations of protoplanetary discs in 30 million years of ripe old age. Presenting the first detailed chemical analysis of long-lived discs using NASA’s James Webb Space Telescope, this paper provides new insights into the formation of planets and the habitability of planets outside the solar system.

“In a sense, Protoplanetary Discs provide photos of babies in the planetary system, including glimpses of what our solar system looks like in its early stages,” said Long, the paper’s lead author and Sagan Fellow of the Priest b and Planetary Lab.

As long as the stars have a certain mass, high-energy radiation from young stars can no longer function as a raw material for building planets, as long as they have a certain mass.

The team observed the official designation of wise J044634.16–262756.1b (the star known more conveniently as J0446B). Researchers have discovered that the planet-forming disks have been around three times longer than expected.

“We know that most disks are distributed within 10 to 20 million years, but we’ve seen that for certain types of stars, the disks can last much longer,” Long said. “Because the materials in the disc provide raw materials to the planet, the lifespan of the disc determines the time the system forms the planet.”

The small star holds the disc for a long time, but the chemical makeup of the disc does not change significantly. Regardless of age, similar chemical compositions indicate that chemistry does not change dramatically even as the disc reaches older age. Such a long lifespan and stable chemical environment can form more time on planets around low-mass stars.

By analyzing the gas content of the disc, the researchers ruled out the possibility that the disc around J0446B is a so-called fragmentary disk.

“We detected gases like hydrogen and neon, indicating that there is still primitive gas remaining on the discs around J0446B,” said Chengyan Xie, a doctoral student at LPL.

According to the author, the presence of gas-rich, long-life discs affects life outside the solar system. Of particular interest to researchers is the Trapist-1 system, located 40 light years from Earth, consisting of a star of the Red Star and seven Earth-like planets. Three of these planets are in “a habitable zones” and offer the possibility that liquid water exists, at least in principle, life will form.

The existence of long-lived discs is of particular interest in the evolution of planetary systems, as stars with long-lived planetary discs fall into a similar mass category as central stars in the trappist-1 system.

“To achieve a specific arrangement of orbitals seen in Trapist-1, the planet needs to move into the disk, a process that requires the presence of gas,” said Ilaria Pascucci, professor of planetary science at LPL, who co-authored the study. “The long presence of gas we find on these discs may be the reason behind Trapist-1’s unique arrangement.”

Stars in such systems evolved much faster and less planetary formation times, so long-lived discs were not found on high-mass stars such as the Sun. Although our solar system took a different evolutionary route, the authors pointed out that long-lived discs can tell researchers much about the universe.

“A better understanding of how low-mass star systems evolve and take snapshots of long-lived disks may help open up ways to fill in the blanks in the universe’s photo album,” Long said.