For billions of years, the Earth has remained relatively stable within our solar system. However, astrophysical simulations do suggest that this tranquility may not last forever.
Astronomers have uncovered a hidden danger lurking in the vastness of space: the gravitational influence of passing field stars.
Field Stars
A field star is a star that appears in the same region of the sky as another object being studied – like a galaxy or a star cluster – but is not physically associated with it. It just so happens to lie along the same line of sight from our perspective on Earth.
For example, you’re observing a distant galaxy through a telescope and you might see some bright stars in the foreground. Those are likely ‘field stars’ – members of our own Milky Way that just happen to be in the way, photobombing your cosmic snapshot.
Field stars are useful too! Astronomers often use them for calibration, comparison, or even to help subtract background light when analyzing deep-sky objects.
Passing stars are an important driver of Paleoclimate and the Solar system’s orbital evolution.
These celestial wanderers, moving through interstellar space, could disrupt the delicate gravitational balance of our solar system.
The consequences could be catastrophic.
Passing Field Stars: A Cosmological Near-Miss?
A passing field star could hypothetically nudge another planet into a collision course with Earth, eject our world into the cold, unforgiving void, or even send it hurtling into the Sun. While these events are improbable, they are far more likely than previously believed, revealing an unsettling vulnerability in our planetary neighbourhood.
Scholz’s star is a binary system discovered in 2013. The system passed through the Solar System‘s Oort cloud roughly 70,000 years ago in a stellar encounter.
It remains unclear whether the near-miss was close enough to give objects in the Oort Cloud, our solar system’s halo of dormant comets, a gravitational nudge to fall toward the Sun. But the interstellar trespasser highlights a sometimes-forgotten reality.
On long time scales, stars seem to fly around like sparks from a campfire, occasionally coming close enough to disturb each other’s cometary clouds. Such close passes could have profound implications for exoplanets – planets orbiting other stars – and how they got where they are.
At least some of the time, an interloper could become a thief, stripping a star of one or more planets, or vice versa.
Mercury: The Catalyst of Chaos
At the heart of this potential disaster is Mercury, the smallest and most volatile of the inner planets. Mercury’s orbit is already somewhat elliptical, but gravitational nudges from Jupiter exacerbate this instability over time.
Now, researchers have discovered that passing field stars can push Mercury’s orbit even further into chaos.
Once Mercury’s orbit destabilizes, the results are catastrophic.
The simulations predict that Mercury could collide with the Sun or Venus, triggering a domino effect of destruction.
Passing field stars increase the odds of Mercury’s instability by about 50-80%.
Venus and Mars, affected by the chaos, may then slam into Earth, send our planet spiraling into the sun, or fling it into deep space, lost forever.
A Cosmic Gamble for Earth: How Passing Field Stars can Reshape the Solar System
Stars jostling around the galaxy are not quite like a cosmic game of pool. But they do have occasional near misses as they speed past each other.
Back when spears and stone points were the height of human technology, astronomers say, our solar system had a close encounter of the interstellar kind.
Thankfully, humanity does not need to worry about these upending cataclysmic events happening anytime soon.
Based on new simulations conducted by astronomers Nathan Kaib and Sean Raymond, the probability of Earth suffering a catastrophic fate within the next 5 billion years is only about 0.2 %.
That’s a long shot – but it is still significantly higher than previous studies suggested.
Why the discrepancy?
Earlier models underestimated the role of passing stars, treating our solar system as an isolated system. In reality, stars move through the Milky Way and occasionally pass close to our solar system.
These intruders subtly tug on the planets, changing their trajectories in ways that could, over immense timescales, lead to disaster.
The Three-Body Problem: Why Chaos is Inevitable
This growing understanding of planetary instability ties into one of Physics’ most infamous challenges: the three-body problem.
In simple two-body systems – such as Earth orbiting the Sun – the movement is predictable and stable.
But introducing a third gravitational influence creates a chaotic and unpredictable system.
In our solar system, we see this phenomenon everywhere: Jupiter influencing Mercury, Venus affecting Earth, and passing stars amplifying these gravitational complexities.
The three-body problem means that even tiny changes in initial conditions can lead to wildly different outcomes.
Therefore, making precise long-term predictions nearly impossible. It is this unpredictability that allows for catastrophic scenarios, even if they seem improbable over human lifetimes.
Stellar Encounters: How Close is Too Close?
What kind of stars pose the greatest risk to the solar system? Kaib & Raymond’s study suggests that the most dangerous intruders are stars that pass within 100 times the distance between Earth and the sun.
These close encounters have a 5 % chance of occurring in the next 5 billion years.
Beyond proximity, a passing field star’s speed also plays a role.
Slower-moving stars – traveling at less than 10 kilometres per second relative to the Sun – linger longer, increasing the duration and strength of their gravitational effects.
These stellar encounters, although rare, could permanently alter the solar system’s structure, reshaping planetary orbits in ways that may eventually spell disaster.
Pluto: A Planetary Outcast at Even Greater Risk
If there is another celestial object facing an even greater risk than Earth, it is Pluto.
Unlike the inner planets, Pluto has a unique orbital relationship with Neptune – it is locked in a 3:2 resonance.
For every three Neptune orbits, Pluto completes two.
This resonance keeps Pluto safe from collisions with Neptune.
While in two-dimensional space it appears that both planets’ orbits intersect, Pluto’s elliptical orbit is tilted 17° to the ecliptic. In 3-D, it becomes clearer that the planets are never in the same place at the same time.
Passing stars have the potential to disrupt this careful balance, knocking Pluto out of its resonance with Neptune. If that happens, Pluto could collide with another planet or be ejected from the solar system entirely.
Over the next 5 billion years, the chance of this fate befalling Pluto is about 4 % – twenty times greater than the risk facing Earth.
A Solar System in Orbital Evolution…
While planetary catastrophes remain unlikely in the short term, the long-term future of the solar system is far from stable.
The gravitational influences of passing stars and the inherent instability of multi-body systems ensure that our planetary arrangement is never truly secure.
For now, Earth remains safe. But as the Sun ages and more passing stars drift through our cosmic neighborhood, our planet’s fate – whether collision, ejection or fiery destruction – may ultimately be sealed by forces far beyond humanity’s control.
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