NASA’s James Webb Space Telescope Discovers Ancient Planet Formation Lasted Longer Than Expected

This is a James Webb Space Telescope image of NGC 346, a massive star cluster in the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbors. With its relative lack of elements heavier than hydrogen and helium, the NGC 346 cluster serves as a nearby proxy for studying stellar environments with similar conditions in the early, distant universe. Ten, small, yellow circles overlaid on the image indicate the positions of the ten stars surveyed in this study.

NASA’s powerful James Webb Space Telescope has finally solved a decades-old puzzle stemming from a controversial Hubble Space Telescope discovery.

Back in 2003, the Hubble Space Telescope made a startling discovery: a massive planet orbiting a star nearly as old as the universe itself. This finding was deeply puzzling. These ancient stars are composed primarily of light elements, with very little of the heavier “building blocks” needed to form planets. Yet, this planet had not only formed but had grown to a colossal size, exceeding even Jupiter. This discovery challenged existing theories of planet formation.

To answer this question, researchers used Webb to study stars in a nearby galaxy that, much like the early universe, lacks large amounts of heavy elements. They found that not only do some stars there have planet-forming disks, but that those disks are longer-lived than those seen around young stars in our Milky Way galaxy.

“With Webb, we have a really strong confirmation of what we saw with Hubble, and we must rethink how we model planet formation and early evolution in the young universe,” said study leader Guido De Marchi of the European Space Research and Technology Centre in Noordwijk, Netherlands.

In the early universe, stars formed from mostly hydrogen and helium, and very few heavier elements such as carbon and iron, which came later through supernova explosions.

“Current models predict that with so few heavier elements, the disks around stars have a short lifetime, so short in fact that planets cannot grow big,” said the Webb study’s co-investigator Elena Sabbi, chief scientist for Gemini Observatory at the National Science Foundation’s NOIRLab in Tucson. “But Hubble did see those planets, so what if the models were not correct and disks could live longer?”

To investigate this, scientists directed the NASA Webb telescope toward the Small Magellanic Cloud, one of the Milky Way’s closest galactic neighbors. Their target was the massive star-forming cluster NGC 346, which, like the early universe, is relatively devoid of heavier elements. This cluster provided a nearby analog for studying early star and planet formation. Building on Hubble observations from the mid-2000s, which showed many stars in NGC 346, aged 20 to 30 million years, still retaining planet-forming disks, the scientists sought to further explore this contradiction of the conventional wisdom that such disks dissipate within just 2 to 3 million years.

“The Hubble findings were controversial, going against not only empirical evidence in our galaxy but also against the current models,” said De Marchi of NASA. “This was intriguing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of disks, or just some artificial effects.”

For the first time, thanks to NASA Webb’s powerful sensitivity and resolution, scientists have obtained spectra of forming, Sun-like stars and their immediate environments in a nearby galaxy.

“We see that these stars are indeed surrounded by disks and are still in the process of gobbling material, even at the relatively old age of 20 or 30 million years,” said De Marchi. “This also implies that planets have more time to form and grow around these stars than in nearby star-forming regions in our own galaxy.”