The solar system may have lost the original “Planet Nine”

That of the solar system current planetary orbits seem stable, but that’s only because planets have settled there for billions of years. The early solar system was a very different place than what we see today, and for nearly 20 years scientists thought they had a good idea of ​​how it got there. But more recently, data has begun to highlight some flaws in that understanding, particularly about how the giant planets of the outer solar system got to where they are today.

Now an international team of astrophysicists believe they have a better understanding of this process, and they think it could help resolve a long-standing debate about the early solar system.

Currently, the best model available to scientists for the formation of the solar system is known as the Nice model, after the city in France, where it was first developed in 2005. As part of this model, the gas giants that currently reside outside the fringes of this solar system originally orbited what became the Sun much more closely with more circular orbits. However, something caused instability in the system that propelled these planets into the much more unevenly spaced and oblong orbits in which we see them today.

The exact cause of this anomaly is so far a mystery. However, a team made up of researchers from Michigan State University, Zhejiang University and the University of Bordeaux believe they have an answer. It’s as simple as dust in the (solar) wind.

At the start of the solar system, the gas giants sat in a dusty cloud around the nascent sun in nearly circular orbits. When the sun lit up, it began to sweep dust from the circumstellar disk. Some of this dust has passed beyond orbit or gas giants, causing the instability that the Nice model sees.

However, the way the researchers fleshed out the idea also solves some problems with the Nice model. One of the main ones was that data, such as that collected from moon samples, pointed to a much faster path to this instability than was typically found in the original Nice model. With this updated “inside-out” dust cloud evaporation model, the arduous journey of hundreds of millions of years of this instability is condensed into a timeline of a few million years, which fits much better to existing data.

That’s not the only data it matches well with, however. The Nice model itself is partially controversial because it points to a potential ninth planet early in the solar system – and that doesn’t mean Pluto. A favorite of many conspiratorial skywatchers, Planet 9 (or Planet X) has garnered increasing attention after a 2015 Caltech study revealed there could be something huge lurking about 50 billion kilometers from the Sun.

Author Sean Raymond of the University of Bordeaux demonstrates how dispersion can have a massive effect on surrounding material.Credit – Sean Raymond/MSU

The original Nice model actually works best with five gas giant inner planets, but in these calculations one of those planets is ejected into interstellar space to become a rogue planet. In the updated model, the result of planetary orbital alignment is essentially the same whether there are four or five starting gas giants in the system. However, they correspond slightly better to reality if there are only four planets initially introduced into the model.

As with many theories, this new model could potentially impact our understanding of the formation of the early solar system and could resolve a long-standing debate over the initial trigger for the instability that has shaped our planetary neighbors so much. But ultimately, even this new model will have to account for the data, and there’s still a lot to collect before the true story of our early solar system is clear.

This article was originally published on Universe today by Andy Tomaswick. Read the original article here.

Arline J. Mercier