Small changes to Neptune’s orbit by a passing star could destroy the entire solar system

Small changes to Neptune’s orbit by a passing star could destroy the entire solar system

Artist's impression of two planets colliding.  Image Credit: Johan Swanepoel/

Artist’s impression of two planets colliding. Image Credit: Johan Swanepoel/

How stable is the solar system? In relative human and historical terms it is quite stable but small gravitational influences can have dramatic effects due to the chaotic and complex nature of the forces involved. Now two researchers set out to determine just how easily it could be disrupted. And the answer is fascinating.

For things to get really bad for the solar system, all it would take is for the average distance between Neptune and the Sun to be changed by 0.1%, which would increase the chances of the solar system descending into chaos tenfold.

The work is accepted for publication in the monthly notices of the Royal Astronomical Society and can be read on the ArXiv paper repository.

One of the possible starting points for the instability of the solar system is the smallest of the planets, Mercury. The perihelion – the closest point in a planet’s orbit around the Sun – of Mercury moves about 1.5 degrees every 1,000 years, a rate very close to that of Jupiter.

If the two were to fall into synchronization – resonance – there is a 1% chance that Mercury would be pulled out of orbit and either ejected from the solar system or placed on a collision course with Venus, the Sun, or even Earth within the next three to four billion years.

Letting things evolve naturally is fine, but there could be ways to create such instability and mess up the solar system. Scientists envision a passing star getting a little too close for comfort. Mercury is too close to the Sun to sense it, but Neptune would, and the disturbance would spread through the solar system.

The effects of a 0.1% disturbance – equivalent to 4.5 million kilometers (2.8 million miles) in Neptune’s semi-major axis – spread to Earth and Mars in just 20 million of years. A 10% disruption could spell disaster for us and the Red Planet.

The team ran 2,880 simulations, including 960 with disturbances too small to measure. Yet in four of them, Mercury hit Venus. It’s not all death and destruction in the other 1,920 models, but there are 26 that end with chaos unfolding, lots of collisions between Mercury and Venus, one with Earth and Mars , colliding with each other, and some where Uranus, Neptune or Mercury is completely expelled.

The team also estimated the likelihood of a star getting close enough to cause all of this and we can rest easy that there’s only about a 20 chance over the next 100 billion years.

Knowing the Sun as it is will only stay for five years, if there is anything disturbing the solar system, it is probably coming from within.

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