In the far reaches of the solar system, there are many icy objects that resemble snowmen, or spheres joined together. Now, new research reveals the simple way these mysterious objects form.
beyond the orbit of Neptune Ice blocks from dawn are lying solar system They are known as planetesimals. Just as snowballs are made up of chunks of snowflakes, planetesimals likely arose within the dust disks that surrounded newborns. solar From a cloud of pebble-sized objects pulled together by mutual gravity.
NASA in 2019 new horizons For the first time in history, a spacecraft captured close-up image They are planetesimals shaped like two connected spheres, or snowball-like objects known as contact binaries. Other research They found that between one-tenth and one-fourth of planetesimals may be contact binaries.
But how this remote snowbank formed remained a mystery. Previous work has attempted to calculate how contact binaries arise by modeling them as colliding spheres. However, until recently, these calculations involved full coupling and always produced spheres rather than other shapes.
In the new study, the researchers instead modeled planetesimals as clouds of particles resting on each other’s surfaces.
“This method is computationally more expensive than traditional full-merger models because we need to track many individual particles that make up a planetesimal, rather than just one large planetesimal-sized particle,” study lead author Jackson Burns, a planetary scientist at Michigan State University, told Space.com.
The new modeling work showed that as these clouds rotate, they sometimes form two separate planetesimals, each orbiting the other, rather than merging into one planetesimal. (Astronomers have observed many binary planetesimals like this. kuiper belt Beyond Neptune. )
In new simulations, these binary planetesimals could spiral inward due to their mutual gravity, eventually gently touching and merging. “What’s great about this model,” Burns said, is that it can create not only spherical planetesimals, but also flat, cigar-shaped, and even snowman-shaped planetesimals. The speed at which these planetesimals move and the strength with which their particles become entangled help determine how they ultimately coalesce.
Burns explained that the pairs of planetesimals that make up these distant snowballs are unlikely to collide with anything else, so they could possibly stay together for millions or even billions of years. Without conflict, there is nothing to separate them.
A new study found that only 4% of simulated planetesimals were made up of contact binaries. “This is not at all consistent with the 10 to 25 percent hypothesis we would expect,” Burns said.
Burns noted that the team’s computer simulations were limited by the number and size of the particles that make up the clouds of pebbles that form planetesimals. Increasing the number and size range of particles in the simulations could help increase the number of contact binaries that can form, he suggested.
A cloud of rotating pebbles could also form three or more planetesimals orbiting each other, “which I think is pretty cool,” Burns said. “This is currently being investigated in more detail, particularly regarding the construction of the triple system and its relationship to the population of relic triples currently observed in the Kuiper belt.”
scientists explained in detail their discoveries Published in the Monthly Journal of the Royal Astronomical Society on February 19th.