Scientists have simulated scenarios where a nearby star, passing close enough to nudge Neptune’s orbit by just 0.1%, could throw the solar system into chaos. Such an event, known as a “stellar flyby,” is not uncommon in the universe and could have dramatic consequences for planetary orbits.

If a passing star slightly shifts Neptune’s position, it might align Mercury and Jupiter’s closest approach to the Sun, known as their perihelion. This alignment could destabilize Mercury’s orbit, leading to two possibilities: either Mercury is ejected from the solar system or it collides with Venus, Earth, or the Sun.

The study, published in Monthly Notices of the Royal Astronomical Society, simulated 3,000 such scenarios. In 26 cases, the disruptions led to planets smashing into each other or Uranus, Neptune, or Mercury being completely ejected from the solar system. These events unfold over millions of years, making the immediate threat negligible.

Stellar flybys are more common during the early stages of a planetary system’s development, typically within the first 100 million years when the system resides in a dense star cluster. As the cluster disperses, the frequency of these close encounters diminishes, reducing their impact on planetary stability.

Garett Brown, a graduate student at the University of Toronto’s Department of Physical and Environmental Sciences, explained that while stellar flybys play a crucial role in the early evolution of planetary systems, they are less significant over time. For our solar system, which formed billions of years ago, the likelihood of a catastrophic stellar flyby is relatively low today.

Despite the minimal short-term risk, the solar system faces long-term instability. Over the next five billion years, the Sun will expand and eventually engulf the inner planets, further altering the dynamics of the solar system. Researchers emphasize that while these scenarios are scientifically fascinating, they pose no immediate threat to humanity.

This study highlights how even small gravitational changes can lead to dramatic outcomes over cosmic timescales. As research on planetary systems evolves, understanding the impact of stellar flybys offers insights into the formation and eventual fate of planets in the universe.