The Kuiper Belt is a region on the outskirts of the Solar System filled with icy bodies. Usually the presence of binary systems in it is interpreted as the absence of the presence of chaos in this structure at the beginning of its existence. However, new research suggests that this is not the case.
Role of the Kuiper belt in the evolution of the Solar System
Attempts to understand the structure and evolution of the Solar System’s Kuiper Belt have kept researchers busy since its existence was hypothesized shortly after the discovery of Pluto in 1930. The presence of binary object systems in it is an important indicator because their existence today provides insight into how energetic or turbulent the evolution of the Solar System was at its beginning four billion years ago.
By carefully studying the evolution of binary systems in which the components are far apart, researchers have brought in more physics that reveals much about their architecture and deployment. They found that such systems may not have formed in the original Solar System, as previously thought. Their work was published in the journal Nature Astronomy.
“In the outer reaches of the solar system, there exists a population of binary systems so widely separated that it seemed worth looking into whether or not they could even survive 4 billion years without being [completely] separated somehow,” said Hunter M. Campbell of the University of Oklahoma in the United States.
The Kuiper Belt is a torus-shaped region of the Solar System containing planetesimals and smaller bodies left behind after its formation. It begins at about the orbit of Neptune, which is on average 30 astronomical units (a.u.) away from the Sun, and extends to about 55 a.u., tilting within 10° of Earth’s ecliptic plane.
20 to 200 times more massive than the asteroid belt, it consists of small remnants of the Solar System’s formation – mostly frozen volatiles such as methane, ammonia, and water. Within its boundaries are the dwarf planets Pluto, Eris, Orcus and others. It is believed that there are more than 100,000 Kuiper Belt objects with diameters greater than 100 km.
Existence of ultra-wide binary objects in the Kuiper belt
Cold classical Kuiper belt objects are a class of small bodies with unperturbed orbits beyond the orbit of Neptune; these objects are primitive and store information about the formation of the Solar System. They never migrated, like Neptune, which moved away from the luminary several billion years ago.
This region has the most ultra-wide binary objects – almost a third of the objects in this region are binary objects gravitationally bound to another object, and a few percent of them are ultra-wide binaries (UWBs), which are about 100 km in diameter but separated by tens of thousands of kilometers.
Despite their rarity and vulnerability to perturbations, modern ultra-wide binaries have been used to constrain the minimum distance from Neptune in the early Solar System and the approximate number of kilometer-sized trans-Neptunian objects (TNOs) in the modern Kuiper Belt.
However, it has been implicitly assumed that the architecture of UWBs, with their large distances, originates from the early, original Solar System. But Campbell and his team raised the question of whether there could have originally existed tightly bound binary objects that, due to collisions with TNOs over the centuries, had lost some of their grip on each other and, although still bound, their separation had evolved to be ultra-wide.
However, studies have shown that the number of TNOs that fly through or collide with the current Kuiper belt is too small to create a significant population of UWBs.
Evolution of ultra-wide binary objects in the Solar System
When Neptune migrated away from the Sun (from 24 to 30 a.u.), some of these objects dynamically scattered until they began to interact strongly with the giant outer planets of the Solar System when they were ejected from the Solar System or trapped in the Oort cloud.
Approximately 99-99.9% of the planetesimals of the original belt are thought to have been ejected from the dynamic Kuiper belt, objects that formed much closer to the Sun and migrated to their current orbits when they were pushed out by Neptune. Since it takes at least 10 million years to remove an object from its original belt, Campbell and his colleagues wondered whether the number of cold classical belt crossings of such disturbed TNOs could be much larger than current observations suggest, which would expose the binaries to large gravitational perturbations.
That’s what their modeling of the evolution of the Kuiper belt revealed. It seems that UWBs are not primary, so they cannot constrain the early Solar System as previously thought.
By exposing early binary objects to four billion years of overflights of these different TNO trajectories, they found that “the expansion of tight binary systems was not uncommon in our simulations.”
They calculated that over the 4 billion years of the Solar System’s existence, the passage of TNO would have resulted in an expansion of up to 10% of the moderately dense binary objects in the UWB. But the result does not apply to denser binary systems.
Provided by phys.org
