For a long time, astronomers have tried to know why so many icy bodies within the outer solar system resemble snowmen, with two rounded sections joined together. Researchers at Michigan State University now report evidence pointing to a surprisingly straightforward process that may explain how these unusual shapes form.
Beyond the turbulent asteroid belt between Mars and Jupiter lies the Kuiper Belt, a distant region past Neptune full of frozen remnants from the solar system’s earliest days. These primitive objects, often called planetesimals, are leftover constructing blocks from planet formation. About 10 percent of them are classified as contact binaries, meaning they consist of two connected lobes that give them a snowman-like appearance. Until recently, scientists didn’t understand how such forms could develop naturally.
Recent Simulation Supports Gravitational Collapse
Jackson Barnes, a graduate student at MSU, developed the primary computer simulation able to naturally producing these double-lobed structures through gravitational collapse. His findings were published within the Monthly Notices of the Royal Astronomical Society.
Previous computer models simplified impacts by treating colliding bodies as in the event that they were fluid masses that blended into smooth spheres. That assumption prevented researchers from recreating the distinctive two-part shape seen in touch binaries. Using the high performance computing cluster at MSU’s Institute for Cyber-Enabled Research, or ICER, Barnes created a more realistic digital environment. In his model, forming objects retain their structural strength, allowing them to settle against one another moderately than merge right into a single sphere.
Some earlier explanations relied on rare cosmic events or unusual conditions. While those scenarios are possible, they’d not easily explain why such objects are relatively common.
“If we expect 10 percent of planetesimal objects are contact binaries, the method that forms them cannot be rare,” said Earth and Environmental Science Professor Seth Jacobson, senior writer on the paper. “Gravitational collapse suits nicely with what we have observed.”
NASA Recent Horizons and the Kuiper Belt
Contact binaries gained widespread attention when NASA’s Recent Horizons spacecraft captured close-up images of 1 in January 2019. The pictures led scientists to look at additional Kuiper Belt objects more closely, revealing that about one in 10 planetesimals share this shape. Within the sparsely populated Kuiper Belt, these distant bodies drift with relatively few collisions, allowing fragile structures to survive.
The Kuiper Belt itself is a relic of the early Milky Way, when the galaxy existed as a rotating disc of gas and mud. That ancient material still lingers on this region, including dwarf planets like Pluto, comets, and countless planetesimals.
How Planetesimals Form and Merge
Planetesimals were among the many first sizable objects to form from the swirling disc of dust and pebbles that surrounded the young Sun. Just like how snowflakes stick together to construct a snowball, tiny particles were drawn together by gravity into larger clusters.
As these rotating clouds collapsed, they often split into two separate bodies that began orbiting each other. Astronomers continuously observe such binary planetesimals within the Kuiper Belt. In Barnes’ simulation, the pair regularly spirals inward. As a substitute of colliding violently, the 2 bodies gently come into contact and fuse, preserving their rounded shapes and creating the familiar snowman form.
Why Contact Binaries Survive
Once joined, these objects can remain intact for billions of years. In accordance with Barnes, their long-term stability comes from the low probability of further impacts. Within the distant Kuiper Belt, collisions are rare. And not using a disruptive crash, there’s nothing to separate the 2 lobes. Many binary objects even show few craters.
Although scientists had suspected gravitational collapse played a job in forming contact binaries, previous models lacked the detailed physics needed to check the concept thoroughly. Barnes’ work is the primary to incorporate the crucial processes to successfully recreate them.
“We’re capable of test this hypothesis for the primary time in a legitimate way,” Barnes said. “That is what’s so exciting about this paper.”
Barnes believes the model could also help researchers study more complex systems involving three or more connected objects. The team is currently developing an improved simulation to higher represent how collapsing clouds behave.
As future NASA missions proceed to explore distant regions of the solar system, Jacobson and Barnes expect that much more snowman-shaped worlds could also be discovered.