This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility:
This artist's illustration shows two trans-Neptunian objects in the distant reaches of the solar system. New research examines how a stellar flyby in the early solar system set TNOs on their unusual orbits. Credit: Southwest Research Institute
Trans-Neptunian objects (TNO) are some of our solar system's lesser-known objects. They number in the thousands, and they get their name from their orbits. These dwarf planets orbit the sun at a greater average distance than Neptune does. Pluto is the group's most well-known member, having been demoted from planet to TNO in recent years.
TNOs are relics from the early solar system. They formed in the cold, distant reaches of the protoplanetary disk. Back then, the young solar system was more chaotic and dynamic, and as the giant planets migrated, gravitational interactions shaped the orbits that TNOs follow.
As a result, many follow eccentric orbits that are somewhat inclined to the planetary plane. They make up what is called the scattered disk. TNOs also have one other unusual feature: a complex color distribution from gray to red as revealed by surveys like the Outer Solar System Origins Survey (OSSOS) and the Dark Energy Survey. Astronomers think that's due to the different ices and complex chemicals on their surfaces. Tholins are one of these chemicals, and they're noteworthy for giving Pluto its reddish hue. (Though Pluto is a TNO, it is not part of the scattered disk.)
It's notable that the color distribution isn't random and suggests a correlation with their orbits. So a TNO's color is indicative of where in the protoplanetary disk it formed and its subsequent dynamical interactions with other bodies.
New research to be published in The Astrophysical Journal Letters suggests that TNOs' unusual orbits and colors are the result of a stellar flyby. It's titled "TNO colours provide new evidence for a past close flyby of another star to the solar system," and the lead author is Prof. Dr. Susanne Pfalzner from the Julich Supercomputing Center in Germany. It is currently available on the arXiv preprint server.
"TNOs are remnants of the planets' formation from a disk of gas and dust, so it is puzzling that they move mostly on eccentric orbits inclined to the planetary plane and show a complex red-to-gray color distribution," the paper states. "A close stellar flyby can account for the TNOs' dynamics, but it is unclear if this can also explain the correlation between their colors and orbital characteristics."
If a flyby occurred, it was likely very early in the solar system's history. "The flyby probably took place during the early phases of the solar system in the sun's birth cluster," the authors write. "In such clusters, the stellar density is about 1,000 to a million times higher than the local stellar density, and therefore, close flybys are much more common."
To find out if a flyby can explain these TNO features, the researchers turned to supercomputer simulations. They simulated a 0.8 solar mass star performing a flyby of a disk modeled with 10,000 and 50,000 particles. Astronomers don't know how large the solar system's disk was, but observations of other disks range from about 100 au to 500 au. "We model the effect of a flyby up to a radius of 150 au," the authors write. The simulated perturber star reached a periastron distance of 110 au and was inclined by 70 degrees.
... continue reading