The Mystery of In-Between Planets in Our Solar System

Our solar system is a marvel of cosmic formation, yet it leaves us questioning what happened to the planets we don’t see. Why don’t we have in-between-sized planets in our solar system? This question delves into the fascinating process of planetary formation, the cosmic dust that accretes, and the hypothesis that some solar systems could indeed have intermediate-sized planets. Let's explore this mystery further.

Understanding Planetary Formation

Planetary formation is a complex process that begins with the accretion of cosmic dust in a protoplanetary disk. As this dust accumulates and grows, it forms planetesimals, which eventually collide and merge to form larger bodies. The mass of these bodies increases until they reach a point where gravity prevents further accretion. This results in the formation of planets. However, the sheer randomness of the process can lead to a variety of planet sizes, including the possibility of having in-between-sized planets that we don’t observe in our solar system.

Generated Size Classes in Our Solar System

Our solar system can be conceptually divided into five size groups, beginning with Mercury as the smallest planet. If we continue doubling the diameters, we can define five distinct size categories for our planets:

Mercury Mars Venus and Earth Missing (the hypothetical in-between size) Neptune and Uranus Saturn and Jupiter

Four out of the five size categories are present in our solar system, leaving us to wonder where the "missing" size category went. This raises the question of whether our solar system is unique or if it is the result of a random process.

Random Selection in Planetary Distribution

The absence of intermediate-sized planets in our solar system could be a result of random selection. It’s worth noting that some solar systems do have planets of varying sizes, including super-Earths and super-Jupiters, while others have planets that are either smaller than Earth or larger. The presence or absence of these planets might be influenced by the specific conditions in their respective solar systems. This random variation can explain why in-between-sized planets are not a universal feature of all solar systems.

Exploring the Reasons Behind the Lack of Intermediate Planets

While the exact reason for the absence of intermediate-sized planets in our solar system remains a mystery, there are two possible explanations:

Random Variation: It could simply be that our solar system is an outlier, and the lack of intermediate-sized planets is due to a random process. This means that our solar system might be one of the few that does not have these intermediate planets. Fundamental Differences: On the other hand, there could be fundamental differences in the distribution of planet sizes across different solar systems. Our current understanding of planetary formation is still evolving, and there might be factors we have yet to discover or fully understand.

For instance, the formation of the asteroid belt between Mars and Jupiter is often cited as a potential example of the destruction of a hypothetical intermediate-sized planet. However, this theory is still debated and not definitively proven. The asteroid belt could have formed gradually over time or as a result of various gravitational interactions, but it remains one of the leading hypotheses to explain its presence.

As our understanding of planetary formation improves, we may one day be able to address some of these questions. The exploration of exoplanets and the study of multiple solar systems can provide invaluable insights into the factors that influence planetary size and distribution. So, while we don't have definitive answers yet, the ongoing research in this field offers hope for future discoveries.