Our Solar System contains a large population of icy bodies stretching well beyond the orbit of Neptune. These objects are remnants from the early formation of the Solar System that were scattered outward from their birth location by Neptune. New research from the University of Colorado Boulder may help solve the mystery why so many of these trans-Neptunian icy bodies don’t circle the Sun the way they should.
An artist’s concept of the minor planet Sedna, one of the detached trans-Neptunian objects. Image credit: NASA / JPL-Caltech.
The orbits of extreme trans-Neptunian objects, which astronomers call ‘detached objects,’ tilt and buckle out of the plane of the Solar System, among other unusual behaviors.
Some scientists have suggested that something big could be to blame — like an as-of-yet-unseen ninth planet lurking beyond Neptune — that scatters objects in its wake.
But University of Colorado Boulder astronomer Ann-Marie Madigan and colleagues prefer to think smaller.
Drawing on exhaustive computer simulations, the researchers make the case that these detached objects may have disrupted their own orbits — through tiny gravitational nudges that added up over millions of years.
“The findings provide a tantalizing hint to what may be going on in this mysterious region of space,” Dr. Madigan said.
The scientists used supercomputers to recreate the dynamics of the outer Solar System in greater detail than ever before.
“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,” said Alexander Zderic, a graduate student at the University of Colorado Boulder.
In the process, the team discovered something unusual: the icy objects in their simulations started off orbiting the Sun like normal. But then, over time, they began to pull and push on each other.
As a result, their orbits grew wonkier until they eventually resembled the real thing.
What was most remarkable was that they did it all on their own — the asteroids and minor planets didn’t need a big planet to throw them for a loop.
Comparison of the largest trans-Neptunian objects: Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, 2002 MS4, Orcus and Salacia. Image credit: Lexicon / CC BY-SA 3.0.
“Individually, all of the gravitational interactions between these small bodies are weak. But if you have enough of them, that becomes important,” Dr. Madigan said.
The authors had seen hints of similar patterns in earlier research, but their latest results provide the most exhaustive evidence yet.
In order to make their theory of ‘collective gravity’ work, the outer Solar System once needed to contain a huge amount of stuff.
“You needed objects that added up to something on the order of 20 Earth masses,” Dr. Madigan said.
“That’s theoretically possible, but it’s definitely going to be bumping up against people’s beliefs.”
“One way or another, scientists should find out soon. A new telescope called the Vera C. Rubin Observatory is scheduled to come online in Chile in 2022 and will begin to shine a new light on this unknown stretch of space.”
“A lot of the recent fascination with the outer Solar System is related to technological advances. You really need the newest generation of telescopes to observe these bodies,” Zderic said.
The results were published in two papers in the Astronomical Journal and the Astrophysical Journal Letters.
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Alexander Zderic & Ann-Marie Madigan. 2020. Giant-planet Influence on the Collective Gravity of a Primordial Scattered Disk. AJ 160, 50; doi: 10.3847/1538-3881/ab962f
Alexander Zderic et al. 2020. Apsidal Clustering following the Inclination Instability. ApJL 895, L27; doi: 10.3847/2041-8213/ab91a0
