Soon after the solar system formed, it went through what is known as the Great Separation – the division of the planets into two separate groups.
We weren't around to observe this cosmic rift, but new research has put forward an intriguing hypothesis about how it happened.
Simply put, the Great Separation left our solar system with the smaller planets closest to the Sun (including Earth and Mars) and the larger gas giants – or 'Jupiter planets' – further away (including Jupiter and Saturn).
These two groups of planets differ not only in size, but also in composition: the minor planets are mainly composed of rocks and do not contain organic carbon compounds, while the planets of Jupiter are mainly composed of gas and are rich in organic matter.
'The question is, how did this compositional dichotomy come about?' says planetary scientist Ramon Brasser of Tokyo Institute of Technology in Japan.
“How do you ensure that material from the inner and outer solar system has not been mixed since the beginning of its history?”
So far, we have blamed Jupiter's gravitational effects. According to this idea, the gravity of the massive planet was enough to create a kind of invisible barrier between the inner and outer planets.
But Brasser and his colleagues believe this is not the case. Their calculations point to a ring-like structure forming around the early Sun, creating a disc that acted as a physical barrier between the two types of planetary materials.
“The most likely explanation for this difference in planetary composition is that it arose from the inner structure of this disk of gas and dust,” says geological scientist Stephen Moijsis of the University of Colorado at Boulder.
Computer simulations carried out by the researchers have shown that in the early solar system, Jupiter would not have been large enough to block the flow of rocky material towards the Sun. If Jupiter did not cause the rift, the team had to look for an alternative explanation.
Drives around distant stars. (ALMA / ESO / NAOJ / NRAO)
They found it in data from the Atacama Telescope Array (ALMA) in Chile, where disks of gas and dust were seen around young stars. If such a ring were originally formed around our own star, it could separate gas and dust into separate layers of high and low pressure.
The researchers describe it as a 'pressure bump' capable of breaking material into two distinct groups in the early days of the solar system. In fact, there may have been several rings responsible for creating the rift in planet types.
How materials were sorted in the early solar system is also important knowledge for understanding the origin of life on Earth.
Unlike other terrestrial planets, our system counteracts this trend by enclosing organic materials, suggesting that these separation discs would not necessarily be completely non-intersecting – and volatile, carbon-rich materials could be scattered throughout the separation to create life on Earth.
This is yet another example of how studying growing stellar systems in other parts of the cosmos can tell us more about how our own solar system came into being, and the first hints of life in our solar neighborhood.
The study is published in the journal Nature Astronomy.
