spaceSpace and Physics

How The Solar System Got Its “Great Divide” May Have Just Been Answered


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockJan 14 2020, 17:25 UTC

The Great Divide. Modification on original Wikimedia Common image. CC BY-SA 3.0

Outer space is messy: full of debris, asteroids, and comets scattered between the major planets. But if there's something that is well organized, it’s the distribution of the planets themselves. All rocky planets (like Earth and Mars) are close to the side, all giants planets (like Saturn and Jupiter) are further out.

This "Great Divide" has perplexed scientists for a long time, but the discovery of many other planetary systems has highlighted that our own is closer to the exception rather than the rule. In a new study published in Nature Astronomy, two researchers have a new approach to explain the differences in the inner and outer Solar System, the origin of this divide, and possibly even how life flourished on Earth.


They suggest the partition of the Solar System comes directly from the protoplanetary disk around the young Sun from which planets emerged. The Solar System was divided into two or more parts by the disk, and the materials in these two regions were prevented from mixing, hence the two different types of planets.

The divide is not obvious to look at. It's an empty stretch of space located near Jupiter, which has been long suspected as the culprit that caused it due to its mass acting as a gravitational barrier, preventing any debris getting past it. But simulations conducted in this research exonerate the gas giant: It was not big enough when the division started.  

"The question is: How do you create this compositional dichotomy?" lead author Ramon Brasser, a researcher at the Earth-Life Science Institute (ELSI) at the Tokyo Institute of Technology, said in a statement. "How do you ensure that material from the inner and outer Solar System didn't mix from very early on in its history?"

The astronomers suggest that, based on observations conducted by the ALMA observatory of other emerging star systems, the disk experienced bands of lower and higher pressure gas and dust. These bands would act as distinct sinks allowing material to be collected, and where gravitational pressure eventually formed a planet.


In particular, they think that if the highest pressure region of the disk was situated just beyond the Asteroid Belt, it would create two distinct regions and explain why the material composition of the Solar System's objects can be divided into two types – "terrestrial" and "jovian" – depending on which side they formed. The barrier is not perfect, which is good news as otherwise all those carbon-rich and volatiles substances from the outer Solar System wouldn’t have managed to get through to us, which on Earth, would go on to help form life.

"Those materials that might go to the Earth would be those volatile, carbon-rich materials," co-author Stephen Mojzsi added. "And that gives you water. It gives you organics."

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