Earth Isn’t ‘Super’ Because the Sun Had Rings

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As we explore the universe, astronomers have discovered a lot of the so-called “super-Earths”. These rocky planets may be several times the mass of Earth, and there is no analogue in our solar system. But why is this? Scientists from Rice University may have a hand. By modeling our solar system with a supercomputer, astrophysicist André Isidoro and colleagues showed that the early formation of the rings around the Sun affected 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, particles clump together and their gravity takes over to form asteroids, comets, and planets. About 30 percent of Sun-like stars end up with a giant Earth

To find out what makes us different, the team created a model of the solar system based on the latest astronomical research. They ran simulations hundreds of times, resulting in a solar system very similar to ours, including the asteroid belt between Mars and Jupiter, the stable orbits of the inner planets, the exact mass of Mars (which is often overestimated in other models), and Kuiper belt bodies outside Neptune.

The key to this accurate simulation was to focus on the ‘pressure bumps’. When a star is born, its gravity acts on the protoplanetary disk, pulling material inward. Changes to these particles produce pressure pits in areas where large amounts of vaporized gas are released. This may be what broke our dust and gas disk into distinct rings. We’ve seen similar structures in younger stars several light-years away (like the star HL Tau below), so this is likely a common occurrence in the formation of the Solar System.

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Young Solar System HL Tau as seen by the ALMA Radio Telescope Array.

The team hypothesized that the composition of our little corner of the universe was due to three pressure bumps. Such burrs may occur at the sublimation lines of silicate, water and carbon monoxide – on one side of the line it is solid, and on the other side it is gas. For example, the closest ring to the Sun in the simulation is where silicon dioxide turns into steam. These substances feed the inner planets like Earth, but timing is also an important aspect. In some simulations, the subsequent appearance of the middle water sublimation line (also known as the snow line) resulted in a giant Earth. Maybe that’s what happens in all those other solar systems that have massive rocky planets.

This all happened a long time ago, and it might 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 clouds of gas that obscure instruments such as Hubble. However, the newly launched James Webb Space Telescope operates in the mid-infrared so that it can look through these barriers. The telescope should be ready to go into action later this year.

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