Our solar system's "great divide," the expanse that separates the terrestrial planets (Mercury, Venus, Earth, Mars) from the gas and ice giants (Jupiter, Saturn, Uranus, Neptune) may finally have an origin story.
According to a study published in the journal Nature Astronomy, the distribution of planetary characteristics in our solar system is likely the result of a protoplanetary disk that formed around our young sun some 4.5 billion years ago.
"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 in Japan, 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?"
A jovian bouncer?
Originally, scientists investigating the great divide, which today is a vast void just beyond the asteroid belt, believed that Jupiter had a role in its formation. Could the gas giant's large size have acted as a kind of gravitational bouncer between materials swirling through the solar system? Brasser and co-author Stephen Mojzsis, a professor in CU Boulder's Department of Geological Sciences, decided to find out by using computers to model simulations of Jupiter's role in the early solar system. The data revealed that despite its impressive size, Jupiter just wasn't big enough to prevent rocky material from moving towards the sun.
"We banged our head against the wall," Brasser said. "If Jupiter wasn't the agent responsible for creating and maintaining that compositional dichotomy, what else could be?"
Hints from young stars
Two so-called 'ALMA disks' as seen in infrared light around distant stars. (Photo: ALMA, ESO/NAOJ/NRAO [public domain])
With Jupiter in the clear, the two researchers next turned their attention to observations of young distant stars collected by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Viewed in infrared light, these systems are surrounded by swirling bands that likely contain alternating low and high pressure bands of gas and dust. These bands result in sinks that may have collected the materials necessary to create distinct regions of the solar system.
"The Great Divide [in North America] causes water to drain one way or another," Mojzsis told CNN. "It's similar to how this pressure bump would have divided material in the solar system."
Thankfully, the great divide wasn't a perfect sieve and allowed some precious, life-giving materials to make their way to the inner solar system.
"Those materials that might go to the Earth would be those volatile, carbon-rich materials," Mojzsis said. "And that gives you water. It gives you organics."