As we explore the cosmos, astronomers have discovered 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 that? Scientists at Rice University might have an idea. 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 percent of Sun-like stars end up with a super-Earth
To find out what makes us different, the team devised 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 much like 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. Belt objects beyond Neptune.
The key to this accurate simulation was to focus on “pressure bumps”. When a star is born, its gravity acts on the protoplanetary disk, pulling material inward. Changes in these particles produce pressure surges in regions where they release large volumes of vaporized gas. This may be what broke our disk of dust and gas into distinct rings. We have seen similar structures in younger stars many light-years away (such as the HL Tau star below), so it is possibly a common occurrence 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 bulges would have occurred in the silicate, water, and carbon monoxide sublimation lines; on one side of the line, they are solid and on the other side, gas. For example, the closest ring to the sun in the simulation is where silicon dioxide turns to steam. This fed material to inner planets like Earth, but time 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.
All of this 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 enveloped by clouds of gas that block instruments like Hubble. However, the recently launched James Webb Space Telescope operates in the mid-infrared to be able to peer through such barriers. The telescope should be ready to go by the end of this year.