Space and Physics

We May Have Just Solved A Mystery About The Weird Icy Worlds Beyond Neptune


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockJul 8 2020, 18:39 UTC

Scientists have long struggled to explain the existence of the solar system's "detached objects," which have orbits that tilt like seesaws and often cluster in one part of the night sky. (Credit: Steven Burrows/JILA)

Beyond the orbits of the giant planets in our Solar System lies the Kuiper Belt, a vast and spread out collection of strange, small, icy bodies. Their distribution and the inclination of their orbits has led researchers to believe that a mysterious ninth planet exists very far away from the Sun affecting these objects. However, other researchers disagree with this hypothesis.


In a new study, published in The Astronomical Journal, researchers provide evidence for a different hypothesis without a Planet Nine. They suggest all these tiny ice bodies disrupted their own orbits. This happened due to small gravitational interactions over hundreds of millions of years – but there is a catch. There ought to be a lot of these small worlds out there with a total mass about 20 times the Earth. So far, we haven't observed anything close to that figure.

"Individually, all of the gravitational interactions between these small bodies are weak, but if you have enough of them, that becomes important," co-author professor Ann-Marie Madigan, from Colorado University Boulder, said in a statement.

You would need "objects that added up to something on the order of 20 Earth masses. That's theoretically possible, but it's definitely going to be bumping up against people's beliefs."

Kuiper Belt objects (KBOs) have two peculiar features that are difficult to explain. Their orbit is tilted with respect to the plane of the Milky Way and they seem to cluster in one particular area of the sky. By using supercomputer simulations, the team showed that if there is enough initial mass, it is possible to recreate what we see out there.


"We modeled something that may have once existed in the outer Solar System and also added in the gravitational influence of the giant planets like Jupiter," added lead author Alexander Zderic also from CU Boulder.

The team was pleased to show that the KBOs didn’t need Planet Nine to end up in a similar configuration but the missing mass is a big if in this scenario. So far, the objects discovered are as small as a city or larger than the Moon. They are tens of times the distance between the Earth and the Sun, so seeing them is difficult. New observatories such as the Vera C. Rubin Observatory, which will come online in 2022, will help with this task.

"A lot of the recent fascination with the outer Solar System is related to technological advances," Zderic said. "You really need the newest generation of telescopes to observe these bodies."

Space and Physics