Space is full of surprises, and the most recent of these is: Spirals are the solar system’s favorite shape. Astronomers have uncovered a surprising spiral structure at the edge of our solar system that closely resembles the distinctive shape of our Milky Way.
The discovery was made using NASA’s Pleiades supercomputer. It simulated the behavior of the Oort Cloud — a vast, spherical shell of icy bodies at the edge of our solar system, beyond view. It is so remote that even NASA’s Voyager 1 spacecraft, traveling at about 1.6 million kilometers per day, won’t reach it for another 300 years.
The Oort Cloud is home to countless frozen bodies that occasionally get knocked toward the inner solar system, becoming the comets we see streaking through the sky. But until now, no one suspected these objects sit in a spiral pattern. Astronomers have generally thought of the Oort Cloud as a random collection of icy bodies.
The spiral arms of the Oort Cloud. Imahe: Nesvorný et al., 2025
Unfathomably huge
The simulations indicate that the inner region of the Oort Cloud forms the spiral structure, much like the spiral arms of the Milky Way. This spiral spans approximately 15,000 astronomical units (au) in length. One au equals 150 million kilometers, the distance between our planet and the Sun. So 15,000 of those is unfathomably large.
“We found that some comets in the inner Oort Cloud, found between 1,000 au to 10,000 au, form a long-lasting spiral structure,” Luke Dones, a co-author of the new study, told Space.com. “We were quite surprised. Spirals are seen in Saturn’s rings, disks around young stars and galaxies. The universe seems to like spirals! Only a small fraction of comets in the Oort Cloud are in this spiral, but that’s still billions of comets.”
Why the solar system favors spirals is a mystery. Scientists believe the structure could be due to the complex gravitational influences of the galaxy, passing stars, and even the movement of the solar system itself as it orbits the Milky Way. However, we’re a long way from understanding all the forces at play well enough to explain the tendency for spirals to form.
