Planet-forming disks surrounding stars often last much longer than expected

Long-standing investigations into the birth and formation of stars, planets, and galaxies have given rise to many exciting revelations. One such fascinating area of research is the study of planet-forming disks – the cosmic nurseries that assist in the generation of new planets.

Traditionally, researchers believed that these disks existed for only a brief period in a star’s life. Most estimates suggested that within 10 million years, they would dissipate, leaving behind either fully formed planets or barren remnants.

However, new research is challenging this assumption, and has revealed that some disks can last far longer under specific conditions.

This unexpected discovery opens up fresh possibilities for understanding how planets form and whether long-lived disks might increase the chances that life exists beyond Earth.

Cosmic discovery defies expectations

A team of researchers at the University of Arizona has discovered that planet-forming disks can persist for much longer than previously believed. Their study focused on stars with a mass of one-tenth of the sun or less.

The findings suggest that under these conditions, disks can survive for as long as 30 million years – three times longer than earlier estimates.

This breakthrough was made possible by NASA’s James Webb Space Telescope, which allowed researchers to conduct a detailed chemical analysis of an unusually long-lived disk.

Their study, published in Astrophysical Letters, sheds new light on the timeline of planet formation. The longer a disk survives, the more time it provides for planets to form, which could significantly impact the development of planetary systems.

“In a sense, protoplanetary disks provide us with baby pictures of planetary systems, including a glimpse of what our solar system may have looked like in its infancy,” explained Feng Long, the lead author of the study and a Sagan Fellow at the Lunar and Planetary Laboratory.

The star that changed the timeline

The research focused on a star designated WISE J044634.16–262756.1B, which is more conveniently known as J0446B.

This star, located in the constellation Columba and about 267 light-years from Earth, has managed to hold onto its disk far longer than expected.

Most young stars lose their planet-forming disks within 10 to 20 million years. Yet, J0446B has retained its disk for about 30 million years, making it an anomaly in planetary science.

The team’s analysis suggests that small stars like J0446B might be capable of maintaining their disks for extended periods, allowing planets more time to form and develop stable orbits.

“Because materials in the disk provide the raw materials for planets, the disk’s lifespan determines how much time the system has to form planets,” explained Long.

Stable environment for planet formation

A key finding of this study is that even though these disks last longer, their chemistry stays mostly the same.

The team observed that the gases and dust in the disk remain relatively stable, providing a consistent environment in which planets may form.

This stability is crucial, as it ensures that planets forming around small stars have the necessary materials for an extended period.

By analyzing the gas content in J0446B’s disk, the researchers ruled out the possibility that it was a debris disk.

Unlike protoplanetary disks, debris disks are made of second-generation material formed by asteroid collisions, and do not support the formation of new planets. The presence of primordial gas confirmed that J0446B’s disk was still in its original state.

“We detected gases like hydrogen and neon, which tells us that there is still primordial gas left in the disk around J0446B,” said Chengyan Xie, a doctoral student at the Lunar and Planetary Laboratory.

Implications for life beyond Earth

The discovery of long-lived planet-forming disks has profound implications for planetary systems outside our own.

One of the most intriguing planetary systems for researchers is TRAPPIST-1, which lies 40 light-years from Earth. This system features a red dwarf star surrounded by seven planets similar in size to Earth.

Three of these planets exist in the habitable zone, where conditions could allow for liquid water and, potentially, for life.

The star in the TRAPPIST-1 system is similar in size to J0446B. Scientists think long-lasting disks help shape planets around small stars. The extra gas in these disks might affect how planets move and settle into their orbits.

“To make the specific arrangement of orbits we see with TRAPPIST-1, planets need to migrate inside the disk, a process that requires the presence of gas,” explained Ilaria Pascucci, a professor of planetary sciences at the Lunar and Planetary Laboratory.

“The long presence of gas we find in those disks might be the reason behind TRAPPIST-1’s unique arrangement.”

Why our solar system evolved differently

The sun and bigger stars lose their disks faster. They change quickly, giving planets less time to form. This might be why our solar system looks different from ones around smaller stars.

Even though these stars are different, studying long-lasting disks helps us learn more about processes that take place in space.

Small stars are much more common than larger stars like the sun, so they might help scientists discover how planets form and whether they can support life.

“Developing a better understanding of how low-mass star systems evolve and getting snapshots of long-lived disks might help pave the way to filling out the blanks in the photo album of the universe,” Long said.

New perspective on planet formation

Since planets need time and the right conditions to in order to develop, the discovery that planet-forming discs may last longer raises new questions.

If small stars hold onto their planet-forming materials for longer, they might have a better chance of creating planets where life could exist.

With powerful telescopes, scientists hope to learn even more about these long-lasting disks. This discovery could completely change how we understand the requirements for planets to form and survive.

Researchers will continue studying these cosmic nurseries to learn more about how planets form and whether any of them could be home to life beyond Earth.

The study is published in The Astrophysical Journal Letters.

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