Future trajectories of the Solar System: dynamical simulations of stellar encounters within 100 au (2311.12171v1)

Abstract: Given the inexorable increase in the Sun's luminosity, Earth will exit the habitable zone in ~1 Gyr. There is a negligible chance that Earth's orbit will change during that time through internal Solar System dynamics. However, there is a ~1% chance per Gyr that a star will pass within 100 au of the Sun. Here, we use N-body simulations to evaluate the possible evolutionary pathways of the planets under the perturbation from a close stellar passage. We find a ~92% chance that all eight planets will survive on orbits similar to their current ones if a star passes within 100 au of the Sun. Yet a passing star may disrupt the Solar System, by directly perturbing the planets' orbits or by triggering a dynamical instability. Mercury is the most fragile, with a destruction rate (usually via collision with the Sun) higher than that of the four giant planets combined. The most probable destructive pathways for Earth are to undergo a giant impact (with the Moon or Venus) or to collide with the Sun. Each planet may find itself on a very different orbit than its present-day one, in some cases with high eccentricities or inclinations. There is a small chance that Earth could end up on a more distant (colder) orbit, through re-shuffling of the system's orbital architecture, ejection into interstellar space (or into the Oort cloud), or capture by the passing star. We quantify plausible outcomes for the post-flyby Solar System.

• The paper finds that there is a 92% likelihood that all eight planets retain similar, Hill-stable orbits during close stellar encounters.
• It reveals that Earth’s orbit might shift to cooler (0.28%) or hotter (0.79%) trajectories, altering its potential habitability.
• The analysis shows that Mercury and the ice giants are most prone to ejection or collision due to strong gravitational perturbations.

Future Trajectories of the Solar System: Dynamical Simulations of Stellar Encounters Within 100 AU

The paper "Future trajectories of the Solar System: dynamical simulations of stellar encounters within 100 au" presents a comprehensive evaluation of the Solar System's dynamical stability in the event of a close stellar flyby. Using a suite of N-body simulations, the authors assess the likelihood of stellar encounters within a range of 100 astronomical units and their subsequent impact on the planetary orbits and potential habitability of Earth.

Key Findings

1. Stability of the Solar System: The paper indicates a high probability (92%) that all eight planets will remain on orbits similar to their current ones, with planetary pairs maintaining Hill-stable orbits in the event of a flyby within 100 AU. However, the angular momentum deficit (AMD), indicative of the system's orbital excitation, is a critical measure correlating with system stability.
2. Outcomes of Stellar Flybys: The research identifies several possible evolutionary paths for the Solar System contingent on the impulse gradient induced by the passing star. There exists a small probability (0.28%) that Earth might end up on a cooler orbit, potentially extending its habitation timeline. However, there is also a higher probability of Earth being perturbed onto a hotter orbit (0.79%).
3. Planetary Loss and Dynamics: Mercury, due to its dynamical fragility, has the highest probability of being ejected or colliding with the Sun. On the other hand, ice giants like Uranus and Neptune are more susceptible to being ejected due to their larger orbital semi-major axes. The paper explores the dynamics leading to planetary ejections and collisions, attributing these phenomena to strong gravitational perturbations.
4. Capture and Escape Scenarios: Occasionally, close encounters result in the capture of one or more planets by the passing star, with these being more probable during slower and massive stellar flybys. The paper also explores the prospects of planets being ejected into interstellar space, examining the implications for potential climates and habitability if a planet like Earth were to be ejected with a substantial atmosphere.
5. Earth-Moon System Stability: A subset of simulations including the Earth-Moon as separate entities indicates increased susceptibility to destabilization, primarily through Moon-stripping events or Earth-Moon collisions, though these outcomes are relatively rare.

Implications and Future Work

This paper is vital for understanding the long-term dynamical evolution of planetary systems in clustered stellar environments, such as the Sun's birth cluster. The analysis stresses the importance of stellar flyby parameters, particularly the impulse gradient on determining outcomes. The findings may also shed light on the orbital architectures of exoplanetary systems and the role stellar encounters play in shaping them.

For future investigations, incorporation of binary star systems and a more intricate model of the Galactic environment could refine these predictions. Additionally, extending the simulation timeframes and tracking the fate of ejected planets could offer deeper insights into interstellar object populations and their potential for habitability.

Overall, the paper articulates a detailed exploration of solar-planetary dynamics, providing a framework to better comprehend the residential timeframes of habitable conditions on Earth and similar planets under the cosmic influence of passing stars.