Scientists have unlocked one of the solar system’s many secrets from an unexpected source: a planetarium show opening to the public on Monday.

At the American Museum of Natural History last fall, experts were hard at work preparing “Encounters in the Milky Way,” a deep dive into our home galaxy shaped by the movements of stars and other celestial objects.

They were fine-tuning a scene featuring what’s known as the Oort Cloud, a region far beyond Pluto filled with icy relics from the solar system’s formation. Comets can hurtle toward Earth from the cloud, but scientists have never glimpsed its true shape.

One evening while watching the Oort Cloud scene, scientists noticed something strange projected onto the planetarium’s dome.

“Why is there a spiral there?” said Jackie Faherty, an astrophysicist who leads the museum’s educational programs and helped put together the planetarium show.

The inner section of the Oort Cloud, made of billions of comets, resembled a bar with two waving arms, similar to the shape of our Milky Way galaxy.

Scientists had long thought the Oort Cloud was shaped like a sphere or flattened shell, warped by the push and pull of other planets and the Milky Way itself. The planetarium show hinted that a more complex shape could lie inside.

The museum contacted the researcher who provided the Oort Cloud data for the show, who was also surprised to see the spiral.


“It’s kind of a freak accident that it actually happened,” said David Nesvorny with the Southwest Research Institute.

Realizing they’d stumbled on something new, the researchers published their findings earlier this year in The Astrophysical Journal.

The spiral is “a striking shift in our understanding of the outer solar system,” planetary scientist Andre Izidoro with Rice University, who was not involved with the study, said in an email.