How planets evolve into the diversity of worlds we see in the universe remains one of the most pressing questions for scientists trying to understand how we got here and where we are headed.
Now, a team of scientists has used data from the Webb Space Telescope to solve a puzzle raised by a veteran space telescope more than 20 years ago that has upended planetary scientists’ understanding of how the earliest worlds formed from the cosmic ether.
In 2003, the Hubble Space Telescope discovered the oldest known planet, a massive world about 13 billion years old. This discovery raised the question of how such worlds are born when their stars were similarly young and contained only a small amount of heavy elements, a crucial component in the formation of planets as we know them.
In the new study, the team used the Webb Space Telescope – a state-of-the-art space observatory capable of observing some of the earliest light sources ever detected – to study stars in a nearby galaxy that are similarly lacking in heavy elements. The team found that these stars have planet-forming disks, and these disks are older than the disks around young stars in our galaxy.
“With Webb, we have a very strong confirmation of what we saw with Hubble, and we have to rethink how we model planet formation and early evolution in the young Universe,” said Guido De Marchi, a researcher at the European Space Research and Technology Center and lead author of the study, in a NASA press release.
In the new study, published in the Astrophysical Journal earlier this month, the team observed stars in NGC 346, a star-forming cluster in the Small Magellanic Cloud. The masses of the stars ranged from about 0.9 times the mass of our Sun to 1.8 times the mass of our host star.
The team found that even the oldest stars they looked at were still accreting gas, and that the stars appeared to have disks around them. This confirmed Hubble observations from the mid-2000s that found stars tens of millions of years old that retained planet-forming disks that were thought to dissipate after a few million years.
Summarizing, the team wrote in the paper that the results “suggest that in low-metal environments, circumstellar disks may live longer than previously thought.”
Researchers believe that the disks may be delayed for several reasons. One is that the absence of heavy elements actually benefits the disks, allowing them to better withstand the pressure of stellar radiation that would otherwise quickly blow them away. Another possibility is that stars like the Sun are formed from large gas clouds that take longer to dissipate simply because they are larger.
“The more matter there is around the stars, the longer accretion takes,” says Elena Sabbi, chief scientist at the National Science Foundation’s Gemini Observatory, part of NOIRLab, in the same release. “Disks are taking ten times longer to disappear. It affects how you shape the planet and the type of system architecture you can have in these different environments. It’s so fascinating.”
The team used the Webb Space Telescope’s Near Infrared Spectrograph instrument (NIRSpec) to study stars scattered across the Small Magellanic Cloud. Last year, a team of scientists used NIRSpec to see muddy clouds on a nearby exoplanet; earlier this year, the instrument was used to detect the first so-called “Einstein zigzag” in space. Unlike the spectrographs on older space observatories, Webb’s NIRSpec can observe 100 objects simultaneously, which accelerates the speed of data collection and, indirectly, discovery.
Studying ancient and young star-forming regions can help clarify the origin of our own solar system, which is about 4.6 billion years old.
