Scaling the Solar System’s Great Divide

Robert Lea
Jan 13 · 4 min read

Probing the origins of the schism that separated the solar system after the Sun formed and may have played a vital role in the formation of life.

Researchers from the US and Japan have uncovered the origins of a great schism that is theorised to have separated the solar system shortly after the Sun firstly ignited. As is fitting for scientists from the University of Colorado Boulder, this ‘Great Divide’ has been compared to the Rocky mountains.

Just as the Rocky Mountains form a divide between East and West in the US, in space, the Great Divide separates planets like Jupiter and Saturn from Earth and Mars.

Whereas this geological barrier — which runs through Colorado, Wyoming, New Mexico and Montana — divides the east and west sides of North America, its altogether more cosmic counterpart separates the terrestrial planets — like Earth and Mars — from the Jovians — such as Jupiter and Saturn. But, this divide is far more than arbitrary, the planets on either side of the Great Divide are composed of radically different materials. The team believe that organic molecules that scaled this divide, were ultimately responsible for the formation of life on Earth.

“The question is: How do you create this compositional dichotomy?” asks Ramon Brasser, lead author of a paper published in Nature Astronomy. The researcher at the Earth-Life Science Institute (ELSI) at the Tokyo Institute of Technology in Japan, continues: “How do you ensure that material from the inner and outer solar system didn’t mix from very early on in its history?”

Along with the paper’s co-author, Stephen Mojzsis, a professor in CU Boulder’s Department of Geological Sciences, Brasser believes he may have the answer. And, as implied above, it may well have important ramifications for the origin of life on Earth.

The duo of researchers believes that the divide was created by a ring-like structure that formed a disc around our young star. This partition separated the early solar-system into two parts. As such it altered the course of evolution of the planets and other bodies such as asteroids — and may have even affected the history of life on Earth.

“The most likely explanation for that compositional difference is that it emerged from an intrinsic structure of this disk of gas and dust,” Mojzsis says. He also notes that this ‘Great Divide’ — a term he and his collaborator coined — looks pretty insignificant today. In fact, it is represented by no more than a band of empty space near Jupiter and beyond the asteroid belt.

The empty space around Jupiter — pictured here by Juno — gave the researchers their first clue as to the existence of the Great Divide in the solar systems distant past. (NASA Jet Propulsion Laboratory/Southwest Research Institute/Malin Space Science Systems)

This band can still be physically traced through the solar system in the relative concentrations of organic molecules — molecules comprised of elements like hydrogen, oxygen, nitrogen and carbon. Using the Great Divide as a starting point and moving inward toward the Sun, an astronomer would note most planets hold low-abundances of organic molecules. Should the astronomer travel in the opposite direction, however, she would observe more bodies in this distant part of the solar system made of carbon-rich matter.

This dichotomy came as a surprise to the researchers who first uncovered it, explains Mojazsis. And, since it was discovered, scientists had always assumed that the disparity was caused by the gravitational influence of Jupiter. They believed that the gas-giant provided a gravitational barrier that blocked dust and larger clumps of matter from making its way towards the sun.

Sceptical of this assumption, Mojzsis and Brasser used a series of computer simulations to model Jupiter’s role in the solar system as it evolved. These simulations indicated to the duo that even as massive as Jupiter is, it still isn’t large enough to completely stem the flow of rocky material towards the Sun, especially in the early stages of its formation.

“We banged our head against the wall,” Brasser adds. “If Jupiter wasn’t the agent responsible for creating and maintaining that compositional dichotomy, what else could be?”

The answer, they discovered, was hiding in plain sight.

The answer was there all along

At the Atacama Large Millimeter/submillimeter Array (ALMA), Chile, astronomers had spotted an unusual phenomenon around distant stars. When observed in infrared wavelengths some young stellar systems were nd to be surrounded by discs of dust and gas that gave them the appearance of a tiger's eye.

This led Brasser and Mojzsis to wonder if a similar ring could have existed in our solar system when it was young — billions of years ago. Were this the case, they reasoned, then it would be plausible that ring could be responsible for the Great Divide, as such a ring would create alternating bands of low and high-pressure gas and dust. These bands could create ‘sinks’ into which the solar system’s early building blocks would be dragged. Of these distinct sinks, one would give way to the Jovians — Saturn and Jupiter — another would create the terrestrials — Earth and Mars.

Brasser and Mojzsis again draw an analogy with the Rocky Mountains. “ In the mountains, the Great Divide causes water to drain one way or another,” Mojzsis says. “It’s similar to how this pressure bump would have divided material” in the solar system.”

The researcher points out that this Great Divide was not a perfect filter, some outer solar system material would have still spilled-over into the inner solar system. And this material — organic molecules remember — would be vital in the evolution of Earth and, in turn, the development of life.

“Those materials that might go to the Earth would be those volatile, carbon-rich materials,” Mojzsis concludes. “And that gives you water.

“It gives you organics.”

Rob is freelance science journalist from the UK, specialising in physics, astronomy, cosmology, quantum mechanics and obscure comic books.

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The Cosmic Companion

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Robert Lea

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Freelance science journalist. BSc Physics. Space. Astronomy. Astrophysics. Quantum Physics. SciComm. ABSW member. WCSJ Fellow 2019. IOP Fellow.

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

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