As we explore the cosmos, astronomers have spotted many so-called “super-Earths”. These rocky planets can be several times more massive than Earth, and there is no analogue in our solar system. But why is this? Scientists at Rice University might have an idea on this. By modeling our solar system with a supercomputer, astrophysicist André Izidoro and his colleagues have shown that the early formation of rings around the sun influenced the size of the resulting planets.
The rings in question are a feature of protoplanetary disks. When a new star forms, its gravity begins to affect nearby clouds of dust and gas. Over time, the particles clump together and their gravity takes over to create asteroids, comets and planets. About 30% of sun-like stars end up with a super-Earth
To find out what makes us different, the team designed a model of the solar system based on the latest astronomical research. They ran the simulation hundreds of times, resulting in a solar system very similar to our own, including the asteroid belt between Mars and Jupiter, stable orbits for the inner planets, accurate mass for Mars (which is often overestimated in other models), and Kuiper girdling objects beyond Neptune.
The key to this accurate simulation was the emphasis on “pressure bumps”. When a star is born, its gravity acts on the protoplanetary disk, pulling matter inward. Changes in these particles produce pressure bumps in regions where they release large volumes of vaporized gas. This may be what split our disk of dust and gas into separate rings. We’ve seen similar structures in younger stars many light-years away (like the star HL Tau below), so this may be a common phenomenon in the formation of the solar system.
The team hypothesized that the composition of our little corner of the cosmos is due to three pressure bumps. These bumps would have occurred at the lines of sublimation for silicate, water and carbon monoxide – on one side of the line they are solid and on the other side gas. For example, the nearest solar ring in the simulation is where silicon dioxide turns into vapour. This has fueled inner planets like Earth with matter, but timing is also an important aspect. In some simulations, a later appearance of the Mean Water Sublimation Line (also called the Snow Line) resulted in the appearance of a super-Earth. Maybe that’s what happens in all those other solar systems that have huge rocky planets.
This all happened so long ago that it may be impossible to find all the answers in our own backyard. To better understand the history of our solar system, it will be necessary to observe as many others as possible. Currently, most young stars are surrounded by gas clouds that block instruments like Hubble. However, the newly launched James Webb Space Telescope operates in the mid-infrared so it can peer through such barriers. The telescope should be ready for operation later this year.
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