In 2003, the Hubble Space Telescope made an intriguing discovery: evidence of a massive planet orbiting an ancient star almost as old as the universe itself.
The James Webb Space Telescope has provided groundbreaking insights into how planets formed in the universe’s infancy, shedding light on a long-standing astronomical mystery. By revisiting findings from the Hubble Space Telescope in 2003, researchers have confirmed that planet-forming disks around certain stars lasted much longer than previously thought, fundamentally challenging our understanding of early planetary evolution.
In 2003, the Hubble Space Telescope made an intriguing discovery: evidence of a massive planet orbiting an ancient star almost as old as the universe itself. This was puzzling because such ancient stars, formed mostly of hydrogen and helium, contain only trace amounts of heavier elements like carbon and iron—the essential building blocks of planets. Existing theories suggested that planets wouldn’t have enough time to grow large under these conditions. Yet, Hubble’s observations hinted otherwise.
To investigate, astronomers turned to the Small Magellanic Cloud, a dwarf galaxy close to the Milky Way that shares chemical similarities with the early universe. Webb’s advanced instruments focused on NGC 346, a young star cluster in this galaxy with relatively few heavier elements. The team aimed to understand how planet-forming disks could persist and support planet formation in such environments.
Surprising Longevity of Planet-Forming Disks
Webb’s observations confirmed that stars in NGC 346, some 20 to 30 million years old, are still surrounded by planet-forming disks—far older than the 2-3 million years typical for similar stars in our Milky Way. This discovery challenges long-standing models that predicted these disks would quickly dissipate due to the lack of heavier elements.
“We see that these stars are still gathering material from their disks even after tens of millions of years,” explained Guido De Marchi, the study’s lead researcher from ESA. “This gives planets more time to grow, defying conventional expectations.”
This finding aligns with earlier Hubble data but provides new clarity thanks to Webb’s ability to capture high-resolution spectra. The spectra confirmed that stars in NGC 346 are actively accreting material, solidifying the evidence that their disks persist far longer than expected.
Why Do These Disks Last Longer?
The longevity of these disks likely stems from two factors, the researchers propose:
- Low Heavy Element Content
Radiation pressure, which disperses disks, relies on heavier elements in the gas. In environments like NGC 346, where heavier elements are only 10% as abundant as in the Sun, the process takes much longer. - Larger Initial Gas Clouds
Stars forming in such environments may start with larger gas clouds, leading to more massive disks. These larger disks take significantly more time to dissipate, providing ample time for dust and gas to coalesce into planetary cores.
“This discovery reshapes our understanding of how planets form under extreme conditions,” said co-researcher Elena Sabbi of NSF’s NOIRLab. “In environments scarce in heavy elements, planets not only form but have time to grow larger, leading to potentially different planetary architectures.”
These findings have far-reaching implications. If disks in environments with few heavy elements last longer, it could explain the formation of massive planets in the universe’s early days, providing a blueprint for how planetary systems evolve in extreme conditions.
Webb’s data paves the way for future studies, offering insights into how stars and planets formed when the universe was still young. It also opens new possibilities for understanding exoplanetary systems in metal-poor regions, which might reveal entirely different planetary structures and dynamics.
