The Before Times of a Solar System
New observations of young stars capture the cosmic forces that can transform tiny particles into colossal worlds.
Many moons ago, before the pandemic—before we even had moons—our home in the universe was a ring of glowing material, with the young sun in the center, like a donut sprinkled with cosmic dust and gas. Round and round the disk went, whisking particles around, until the material began to stick together in clumps. After millions of years, the clumps curved into the planets and the moons as we know them today, a rich assortment of worlds.
This is our story, but it has happened—is happening—countless times across the cosmos, around other stars. Astronomers have long known about such swirling structures, known as protoplanetary disks, which are the leftovers from the fiery birth of new suns. Telescopes have even managed to observe them in stunning detail (well, as stunningly detailed as you can get many light-years from Earth).
The latest batch of images, released this week, offers one of the highest-resolution views of these planetary nurseries yet.
An international team of astronomers has captured images of the innermost rings of disks swirling around 15 stars, many hundreds of light-years away. Previous observations have never glimpsed this part of a protoplanetary disk, quite close to the parent star, this deeply before. To the untrained eye, the disks, shown at the top of this article, might look like bright splotches of oranges and purples. But to astronomers, they are tantalizing splotches of oranges and purples; there, in those blurry pixels close to the star, is where cosmic forces can transform tiny particles into colossal worlds—especially rocky planets like our own.
“It’s an unexplored area,” says Johanna Teske, an astronomer at the Carnegie Institution for Science, who was not involved in the new research.
According to theories of planet formation, a baby planet’s position inside a protoplanetary disk dictates what kind of world it turns out to be. Gaseous worlds—like Jupiter and Saturn—arise farther out from their star, where it’s cold enough for molecules to condense into ice and stay that way. Rocky worlds—like Earth and Mars—coalesce closer in, where the warmth of the star tends to evaporate icy material, but spares bits of rock. The thought of peering into these inner regions and searching for rocky planets, the only planets on which we know that life can arise, is a tantalizing one indeed.
None are visible in these images, mind you, but there are a few hints. Growing baby planets can perturb nearby matter in these disks, twisting and bending it. The indentations in some of the disks could be signs of material gathering in little whirlpools and sticking together, forming clumps with enough gravity of their own to tug at their surroundings.
Astronomers have found similar hints in other, more zoomed-out observations of protoplanetary disks. The rings in images like this one, for example, are likely the result of lurking planets carving a path through the dust and gas as they circle their star.
In 2018, astronomers even captured photographic evidence of a planet bending clouds of dust and gas around its young star, known as HL Tauri, as it swirled into being. They scrutinized the faint light emanating from the planet and discovered that it is an extremely hot, gaseous planet several times the mass of Jupiter. Perhaps another blood-orange-ish splotch to the rest of us, but a momentous discovery to researchers.
Such images are not quite photographs. To capture the inner edges of protoplanetary disks in the latest batch, astronomers blended together starlight absorbed by four different ground-based telescopes. This is a delightful hack in astronomy work: If a telescope isn’t powerful enough to see a target, make a bigger one by syncing a bunch of small telescopes so that they scan the skies as one. (This is the same technique that produced the first-ever image of a black hole, which took 10 telescopes across four continents.)
The researchers then combined those data with mathematical models to reconstruct the finer details of the disks. The final result is a reconstruction of the real thing, though several astronomers who weren’t involved in the research tell me it’s a very good one. According to Jacques Kluska, the lead author of the research and an astronomer at KU Leuven, a university in Belgium, the views of the inner disks would amount to only a few pixels in a direct image from a single, powerful telescope. “These are pretty unprecedented physical scales,” says Kate Folette, an astronomer at Amherst College who uses ground-based telescopes to search for planets around young stars, and wasn’t involved in the latest work.
To peer much deeper into these disks of new beginnings, astronomers would need to use dozens of telescopes to simulate the resolution of an observatory much larger than anything currently in existence. Closer in, they could detect movements, patterns, orbits. They might even discover, in the cosmic fog, a rocky planet gliding at an Earth-like distance from its star. The view would present a perspective equally forward-looking and nostalgic: There would be the thrill of finding a world that might resemble ours, even though we cannot cross the unfathomable expanse to reach it. And there would be the realization of seeing the beginnings of our planet’s own story, like uncovering a photograph from a past we don’t remember. Until then, there is plenty to marvel at in our cosmic neighborhood, all grown up.